Investigation into Structural Phase Transitions in Layered Titanium-Oxypnictides by a Computational Phonon AnalysisClick to copy article linkArticle link copied!
Abstract
We applied ab initio phonon analysis to layered titanium-oxypnictides, Na2Ti2Pn2O (Pn = As and Sb), and found a clear contrast between the cases with lighter/heavier pnictogen in comparison with experiments. The result completely explains the experimental structure at low temperature, C2/m for Pn = As, within the conventional charge density wave, while there arise discrepancies when the pnictogen gets heavier. Our phonon calculation using the GGA-PBE functional predicts that a Cmce polymorph is more stable than the experimentally observed one (Cmcm) for Pn = Sb. On the basis of further quantitative analysis, we suggest the possibility that the GGA-PBE functional does not properly reproduce the electron correlation effects for Pn = Sb, and this could be the reason for the present discrepancy.
Synopsis
We applied ab initio phonon analysis to layered titanium-oxypnictides, Na2Ti2Pn2O (Pn = As and Sb), and found a clear contrast between the cases with lighter/heavier pnictogen in comparisons with experiments. Our phonon calculations completely explain the experimental structure, C2/m for Pn = As, within the conventional charge density wave, while discrepancies arise when the pnictogen gets heavier, with the same trend for BaTi2Pn2O (Pn = As, Sb, and Bi).
Introduction
Figure 1
Figure 1. Crystal structure of Na2Ti2Pn2O (Pn = As and Sb). The space group is I4/mmm.
Results
Figure 2
Figure 2. Electronic band structures for undistorted Na2Ti2Pn2O structure ((a) Pn = As, (b) Pn = Sb). The Fermi energy is set to 0 eV.
Figure 3
Figure 3. Phonon dispersions and phonon DOS for undistorted (I4/mmm) Na2Ti2Pn2O (Pn = (a) As, (b) Sb). The red cross marks in (b) represent the frequencies with spin–orbit coupling.
Figure 4
Figure 4. In-plane superstructures obtained by our calculations for Pn = (a) As and (b) Sb, and (c) the observed in-plane superstructure for Pn = Sb. (28) Pn is located above and below the Ti2O plane. Solid lines represent the original unit cells for I4/mmm. Thin dash lines represent the unit cells for 2 × 2 superstructures. Solid dash lines represent redefined unit cells for distorted superstructures. The conventional lattice vectors of the superstructure for (a) Pn = As (C2/m) are redefined as ,
, and
, those for (b) Pn = Sb (Cmce) are redefined as
,
, and
, and those for (c) Pn = Sb (Cmcm) are redefined as
,
, and
, where
,
, and
are conventional lattice vectors of the undistorted structures.
Figure 5
Figure 5. 3D superstructures obtained from our calculations for Pn = (a) As (C2/m) and (b) Sb (Cmce).
label | x | y | z | wyckoff |
---|---|---|---|---|
Pn = As (I4/mmm) | ||||
Na | 0.50000 | 0.50000 | 0.18146 | 4e |
Ti | 0.50000 | 0.00000 | 0.00000 | 4c |
As | 0.00000 | 0.00000 | 0.11752 | 4e |
O | 0.50000 | 0.50000 | 0.00000 | 2b |
Pn = Sb (I4/mmm) | ||||
Na | 0.50000 | 0.50000 | 0.18369 | 4e |
Ti | 0.50000 | 0.00000 | 0.00000 | 4c |
Sb | 0.00000 | 0.00000 | 0.12015 | 4e |
O | 0.50000 | 0.50000 | 0.00000 | 2b |
The relaxed conventional lattice parameters are a = 4.07 Å, c = 15.44 Å (a = 4.14 Å, c = 16.98 Å) for Pn = As (Sb), giving good agreement with the experiments. (2, 54) The height of Sb toward Ti2O plane obtained from the present calculation is 2.04 Å, which is consistent with the experimental value at room temperature (2.01 Å). (54) For Pn = As, the height of As toward Ti2O plane has not been determined in experiments, but the obtained value (1.81 Å) is quite consistent with the experimental results of BaTi2As2O (1.77 Å) (4) and (SrF)2Ti2As2O (1.81 Å). (3)
label | x | y | z | wyckoff |
---|---|---|---|---|
Pn = As (C2/m) | ||||
Na | 0.90907 | 0.00000 | 0.63699 | 4i |
Na | 0.40943 | 0.00000 | 0.63694 | 4i |
Na | 0.15932 | 0.24981 | 0.63725 | 8j |
Ti | 0.13031 | 0.11979 | 0.00000 | 8j |
Ti | 0.88019 | 0.36969 | 0.00000 | 8j |
As | 0.80877 | 0.00000 | 0.23625 | 4i |
As | 0.30933 | 0.00000 | 0.23625 | 4i |
As | 0.05905 | 0.24969 | 0.23623 | 8j |
O | 0.00000 | 0.00000 | 0.00000 | 2a |
O | 0.25000 | 0.25000 | 0.00000 | 4e |
O | 0.00000 | 0.50000 | 0.00000 | 2b |
Pn = Sb (Cmce) | ||||
Na | 0.18411 | 0.00000 | 0.00000 | 8d |
Ti | 0.00000 | 0.23266 | 0.26812 | 8f |
Sb | 0.37883 | 0.00000 | 0.00000 | 8d |
O | 0.00000 | 0.00000 | 0.00000 | 4a |
The conventional lattice parameters after relaxation are a′=11.51 Å, b′ = 11.51 Å, c′ = 8.23 Å, and β = 110.46° (a′ = 17.04 Å, b′ = 5.84 Å, and c′ = 5.83 Å) for Pn = As (Sb).
Figure 6
Figure 6. Phonon dispersions for Na2Ti2Sb2O superstructure (Cmce).
label | x | y | z | wyckoff |
---|---|---|---|---|
Pn = Sb (Cmcm) | ||||
Na | 0.00000 | 0.37498 | 0.93293 | 8f |
Na | 0.00000 | 0.12503 | 0.43294 | 8f |
Na | 0.74999 | 0.12500 | 0.93275 | 16h |
Ti | 0.37417 | 0.00083 | 0.25000 | 8g |
Ti | 0.62584 | 0.24918 | 0.25000 | 8g |
Ti | 0.87581 | –0.00085 | 0.25000 | 8g |
Ti | 0.12418 | 0.25082 | 0.25000 | 8g |
Sb | 0.00000 | 0.37533 | 0.12909 | 8f |
Sb | 0.00000 | 0.12532 | 0.62908 | 8f |
Sb | 0.75033 | 0.12499 | 0.12907 | 16h |
O | 0.00000 | 0.62500 | 0.25000 | 4c |
O | 0.00000 | 0.12500 | 0.25000 | 4c |
O | 0.75000 | 0.37500 | 0.25000 | 8g |
The conventional lattice parameters after relaxation are a′ = 11.74 Å, b′ = 11.74 Å, and c′ = 16.83 Å.
Discussion



Figure 7
Figure 7. Partial density of states and center of masses of Na2Ti2Pn2O (a) Pn = As, (b) Pn = Sb.
Figure 8
Figure 8. Electron densities of Na2Ti2Pn2O (a) Pn = As, (b) Pn = Sb along Ti–Pn bonds. The electron densities are plotted in the same range (0.03–0.07 electron/bohr3), and the aspects are consistent with each crystal structure.
Figure 9
Figure 9. (a) Change in potential energy accompanying the displacement of Ti atoms according to the phonon showing the imaginary (lowest) frequency at X point in Pn = Sb (As). The horizontal axis corresponds to the magnitude of the displacement from the original positon. (b) Two-dimensional image of the displacement parttern of Ti atoms. (c) Three-dimensional image of the displacement parttern of the Ti atom enclosed in a red broken line in (b).
Conclusions
Computational Details
Figure 10
Figure 10. Primitive Brillouin zones (a) for undistorted Na2Ti2Pn2O structure (I4/mmm) and (b) for Na2Ti2Sb2O superstructure (Cmce).
Acknowledgment
The computation in this work has been performed using the facilities of the Research Center for Advanced Computing Infrastructure (RCACI) at JAIST. R.M. and K.H. are also grateful to MEXT-FLAGSHIP2020 (hp170269, hp170220) for their computational resources. K.H. is grateful for financial support from a KAKENHI grant (JP17K17762), a Grant-in-Aid for Scientific Research on Innovative Areas “Mixed Anion” project (JP16H06439) from MEXT, PRESTO (JPMJPR16NA) and the Materials research by Information Integration Initiative (MI2I) project of the Support Program for Starting Up Innovation Hub from Japan Science and Technology Agency (JST). R.M. is grateful to MEXT-KAKENHI (26287063, 17H05478), a Grant-in-Aid for Scientific Research on Innovative Areas "Mixed Anion" project (JP16H06440), a grant from the Asahi glass Foundation, and US-AFOSR-AOARD for their financial supports.
References
This article references 54 other publications.
- 1Axtell, E. A.; Ozawa, T.; Kauzlarich, S. M.; Singh, R. R. Phase Transition and Spin-gap Behavior in a Layered Tetragonal Pnictide Oxide J. Solid State Chem. 1997, 134, 423 DOI: 10.1006/jssc.1997.7715Google Scholar1Phase transition and spin-gap behavior in a layered tetragonal pnictide oxideAxtell, E. A., III; Ozawa, Tadashi; Kauzlarich, Susan M.; Singh, Rajiv R. P.Journal of Solid State Chemistry (1997), 134 (2), 423-426CODEN: JSSCBI; ISSN:0022-4596. (Academic Press)Spin-gap behavior was obsd. for the 1st time in the layered tetragonal compd. Na2Ti2Sb2O. Na2Ti2Sb2O shows a sharp discontinuity in magnetic susceptibility at 150 K, reminiscent of behavior obsd. in the spin-Peierls compd. CuGeO3. Na2Ti2Sb2O also shows a discontinuity in temp.-dependent resistivity at the magnetic transition and metallic behavior for all other temps., 5.7 mΩ cm at room temp. Ti-Sb-Ti superexchange probably is favored over Ti-O-Ti superexchange, based on the high-temp. magnetic susceptibility data and on the identity of the magnetic orbitals.
- 2Ozawa, T. C.; Kauzlarich, S. M.; Bieringer, M.; Greedan, J. E. Possible Charge-Density-Wave/Spin-Density-Wave in the Layered PnictideOxides:Na2Ti2Pn2O (Pn = As, Sb) Chem. Mater. 2001, 13, 1804 DOI: 10.1021/cm010009fGoogle ScholarThere is no corresponding record for this reference.
- 3Liu, R.; Song, Y.; Li, Q.; Ying, J.; Yan, Y.; He, Y.; Chen, X. Structure and Physical Properties of the Layered Pnictide-Oxides:(SrF)2Ti2Pn2O (Pn = As, Sb) and (SmO)2Ti2Sb2O Chem. Mater. 2010, 22, 1503 DOI: 10.1021/cm9027258Google ScholarThere is no corresponding record for this reference.
- 4Wang, X. F.; Yan, Y. J.; Ying, J. J.; Li, Q. J.; Zhang, M.; Xu, N.; Chen, X. H. Structure and physical properties for a new layered pnictide-oxide: BaTi2As2O J. Phys.: Condens. Matter 2010, 22, 075702 DOI: 10.1088/0953-8984/22/7/075702Google Scholar4Structure and physical properties for a new layered pnictide-oxide: BaTi2As2OWang, X. F.; Yan, Y. J.; Ying, J. J.; Li, Q. J.; Zhang, M.; Xu, N.; Chen, X. H.Journal of Physics: Condensed Matter (2010), 22 (7), 075702/1-075702/5CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)A layered pnictide-oxide BaTi2As2O have been prepd. and characterized. It shares similar characteristics with Na2Ti2Sb2O. The crystal has a layered structure with a tetragonal P4/nmm group (a = 4.047(3), c = 7.275(4) Å). The resistivity shows an anomaly at 200 K, which should be ascribed to an SDW or structural transition. The SDW or structural transition is confirmed by magnetic susceptibility and heat capacity measurements. These properties are very similar to those obsd. in parent compds. of high-Tc iron-based pnictide superconductors where the supercond. shows up when the anomaly due to the SDW or structural transition is suppressed. Li+ doping significantly suppresses the anomaly, but no supercond. emerges.
- 5Doan, P.; Gooch, M.; Tang, Z.; Lorenz, B.; Moeller, A.; Tapp, J.; Chu, P. C. W.; Guloy, A. M. Ba1–xNaxTi2Sb2O (0.0 ≤ x ≤ 0.33) A Layered Titanium-Based Pnictide Oxide Superconductor J. Am. Chem. Soc. 2012, 134, 16520 DOI: 10.1021/ja3078889Google ScholarThere is no corresponding record for this reference.
- 6Yajima, T.; Nakano, K.; Takeiri, F.; Ono, T.; Hosokoshi, Y.; Matsushita, Y.; Hester, J.; Kobayashi, Y.; Kageyama, H. Superconductivity in BaTi2Sb2O with a d1 Square Lattice J. Phys. Soc. Jpn. 2012, 81, 103706 DOI: 10.1143/JPSJ.81.103706Google Scholar6Superconductivity in BaTi2Sb2O with a d1 square latticeYajima, Takeshi; Nakano, Kousuke; Takeiri, Fumitaka; Ono, Toshio; Hosokoshi, Yuko; Matsushita, Yoshitaka; Hester, James; Kobayashi, Yoji; Kageyama, HiroshiJournal of the Physical Society of Japan (2012), 81 (10), 103706/1-103706/4CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)We prepd. a new two-dimensional oxyantimonide, BaTi2Sb2O, which shows a superconducting transition at 1.2 K, representing the first supercond. in a system with Ti3+ (d1) in a square lattice. The TiO2Sb4 mixed anionic coordination stabilizes a unique half-filled Ti dxy orbital configuration in Ti2O plane, which is analogous to Cu2+ (d9) in the high-Tc superconductors. A charge d. wave (CDW)- or spin d. wave (SDW)-like anomaly appears at 50 K, which is significantly reduced compared with 200 K for the isostructural and non-superconducting BaTi2As2O.
- 7Yajima, T.; Nakano, K.; Takeiri, F.; Hester, J.; Yamamoto, T.; Kobayashi, Y.; Tsuji, N.; Kim, J.; Fujiwara, A.; Kageyama, H. Synthesis and Physical Properties of the New Oxybismuthides BaTi2Bi2O and (SrF)2Ti2Bi2O with a d1 Square Net J. Phys. Soc. Jpn. 2013, 82, 013703 DOI: 10.7566/JPSJ.82.013703Google Scholar7Synthesis and physical properties of the new oxybismuthides BaTi2Bi2O and (SrF)2Ti2Bi2O with a d1 square netYajima, Takeshi; Nakano, Kousuke; Takeiri, Fumitaka; Hester, James; Yamamoto, Takafumi; Kobayashi, Yoji; Tsuji, Naruki; Kim, Jungeun; Fujiwara, Akihiko; Kageyama, HiroshiJournal of the Physical Society of Japan (2013), 82 (1), 013703/1-013703/4CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)We have recently reported the d1 square-lattice compd. BaTi2Sb2O, which shows supercond. at Tc = 1.2 K coexisting with a charge- or spin-d. wave (CDW/SDW) state. Here, we successfully prepd. two new oxybismuthides, BaTi2Bi2O and (SrF)2Ti2Bi2O, as the first Pn = Bi compds. in the ATi2Pn2O family. The CDW/SDW state disappeared for both compds., presumably owing to the considerable interaction between the Ti-3d and Bi-6s orbitals. The complete suppression of the CDW/SDW instability resulted in an enhanced Tc of 4.6 K for BaTi2Bi2O. However, (SrF)2Ti2Bi2O exhibits no supercond., suggesting the importance of the interlayer interaction for supercond.
- 8Yajima, T.; Nakano, K.; Takeiri, F.; Nozaki, Y.; Kobayashi, Y.; Kageyama, H. Two Superconducting Phases in the Isovalent Solid Solutions BaTi2Pn2O (Pn = As, Sb, and Bi) J. Phys. Soc. Jpn. 2013, 82, 033705 DOI: 10.7566/JPSJ.82.033705Google Scholar8Two superconducting phases in the isovalent solid solutions BaTi2Pn2O (Pn = As, Sb, and Bi)Yajima, Takeshi; Nakano, Kousuke; Takeiri, Fumitaka; Nozaki, Yasumasa; Kobayashi, Yoji; Kageyama, HiroshiJournal of the Physical Society of Japan (2013), 82 (3), 033705/1-033705/4CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)We have recently reported two superconductors with the d1 square lattice, BaTi2Sb2O (Tc = 1.2 K) and BaTi2Bi2O (Tc = 4.6 K). In order to find a clue behind the supercond. of these materials, we synthesized isovalent solid solns. of BaTi2(As1-xSbx)2O and BaTi2(Sb1-yBiy)2O. Despite Vegard's law behavior in cell consts., a two-dome structure in Tc was obsd. with two distinct superconducting phases ("0.9 ≤ x; y ≤ 0.3" and "0.6 ≤ y ≤ 1") sepd. by a metallic phase. This result implies a multiband nature at the Fermi surface in BaTi2Pn2O.
- 9Zhai, H.-F.; Jiao, W.-H.; Sun, Y.-L.; Bao, J.-K.; Jiang, H.; Yang, X.-J.; Tang, Z.-T.; Tao, Q.; Xu, X.-F.; Li, Y.-K.; Cao, C.; Dai, J.-H.; Xu, Z.-A.; Cao, G.-H. Superconductivity, charge- or spin-density wave, and metal-nonmetal transition in BaTi2(Sb1-xBix)2O Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 100502 DOI: 10.1103/PhysRevB.87.100502Google ScholarThere is no corresponding record for this reference.
- 10Nakano, K.; Yajima, T.; Takeiri, F.; Green, M. A.; Hester, J.; Kobayashi, Y.; Kageyama, H. Tc Enhancement by Aliovalent Anionic Substitution in Superconducting BaTi2(Sb1–xSnx)2O J. Phys. Soc. Jpn. 2013, 82, 074707 DOI: 10.7566/JPSJ.82.074707Google Scholar10Tc enhancement by aliovalent anionic substitution in superconducting BaTi2(Sb1-xSnx)2ONakano, Kousuke; Yajima, Takeshi; Takeiri, Fumitaka; Green, Mark A.; Hester, James; Kobayashi, Yoji; Kageyama, HiroshiJournal of the Physical Society of Japan (2013), 82 (7), 074707/1-074707/5CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)BaTi2Sb2O is a Tc = 1.2 K superconductor with a d1 square lattice, and isovalent Bi substitution for Sb can increase its Tc to 4.6 K (BaTi2Bi2O), accompanied by the complete suppression of charge d. wave (CDW) or spin d. wave (SDW) transition. In the present study, we demonstrate that aliovalent Sn substitution (hole doping) also increases Tc up to 2.5 K for BaTi2(Sb0.7Sn0.3)2O, while suppressing CDW/SDW transition only slightly. The overall electronic phase diagram of BaTi2(Sb,Sn)2O is qual. similar to that of cation-substituted (hole-doped) (Ba,Na)Ti2Sb2O, but quant. differences such as in Tc are obsd., which is discussed in terms of Ti-Pn hybridization and chem. disorder.
- 11Pachmayr, U.; Johrendt, D. Superconductivity in Ba1-xKxTi2Sb2O (0 ≤ x ≤ 1) controlled by the layer charge Solid State Sci. 2014, 28, 31 DOI: 10.1016/j.solidstatesciences.2013.12.005Google Scholar11Superconductivity in Ba1-xKxTi2Sb2O (0 ≤ x ≤ 1) controlled by the layer chargePachmayr, Ursula; Johrendt, DirkSolid State Sciences (2014), 28 (), 31-34CODEN: SSSCFJ; ISSN:1293-2558. (Elsevier Masson SAS)The solid soln. of antimonide-oxides Ba1-xKxTi2Sb2O (0 ≤ x ≤ 1) has been synthesized by solid-state reactions and characterized by X-ray powder diffraction (CeCr2Si2C-type structure; P4/mmm, Z = 1). The crystal structure consists of Ti2Sb2O-layers that are stacked with layers of barium atoms along the c-axis. BaTi2Sb2O is a known superconductor with a crit. temp. (Tc) of 1.2 K. Substitution of barium through potassium raises Tc up to 6.1 K at 12% potassium, while no supercond. emerges with concns. higher than 20%. Anomalies in elec. transport and magnetic susceptibility indicate charge d. wave (CDW) instabilities. The CDW transition temps. (Ta) decrease from 50 K in the parent compd. to 28 K at 10% potassium substitution. No CDW transition was detected at higher concns., and no evidence for a redn. of the lattice symmetry below Ta was found. The lattice parameters vary linearly while the unit cell vol. increases with higher potassium concns. The phase diagrams Tc(x) and Ta(x) of Ba1-xKxTi2Sb2O are remarkably similar to the known series Ba1-xNaxTi2Sb2O (0 ≤ x ≤ 0.33) in spite of the reverse vol. effect. From this we conclude that the charge and not the vol. dets. the phase diagrams of these superconducting antimonide-oxides.
- 12von Rohr, F.; Nesper, R.; Schilling, A. Superconductivity in rubidium-substituted Ba1-xRbxTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 89, 094505 DOI: 10.1103/PhysRevB.89.094505Google Scholar12Superconductivity in rubidium-substituted Ba1-xRbxTi2Sb2Ovon Rohr, Fabian; Nesper, Reinhard; Schilling, AndreasPhysical Review B: Condensed Matter and Materials Physics (2014), 89 (9), 094505/1-094505/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We report on the synthesis and the phys. properties of Ba1-xRbxTi2Sb2O (x ≤ 0.4) by x-ray diffraction, superconducting quantum interference device magnetometry, resistivity, and specific-heat measurements. Upon hole doping by substituting Ba with Rb, we find supercond. with a max. Tc = 5.4 K. Simultaneously, the charge-d.-wave transition temp. is strongly reduced from TCDW ≈ 55 K in the parent compd. BaTi2Sb2O and seems to be suppressed for x ≥ 0.2. The bulk character of the superconducting state for the optimally doped sample (x = 0.2) is confirmed by the occurrence of a well developed discontinuity in the sp. heat at Tc, with ΔC/Tc ≈ 22 mJ/mol K2, as well as a large Meissner-shielding fraction of ≈40%. The isotropically averaged lower and upper crit. fields of the optimally doped sample (x = 0.2) are estd. to μ0Hc,1(0) ≈ 3.8 mT and μ0Hc,2(0) ≈ 2.3 T, resp., indicating that these compds. are strongly type-II superconductors.
- 13Ji, Q.; Ma, Y.; Hu, K.; Gao, B.; Mu, G.; Li, W.; Hu, T.; Zhang, G.; Zhao, Q.; Zhang, H.; Huang, F.; Xie, X. Synthesis, Structural, and Transport Properties of Cr-Doped BaTi2As2O Inorg. Chem. 2014, 53, 13089 DOI: 10.1021/ic502192hGoogle ScholarThere is no corresponding record for this reference.
- 14Bednorz, J.; Müller, K. Possible high Tc superconductivity in the Ba-La-Cu-O system Z. Phys. B: Condens. Matter 1986, 64, 189 DOI: 10.1007/BF01303701Google Scholar14Possible high Tc superconductivity in the barium-lanthanum-copper-oxygen systemBednorz, J. G.; Mueller, K. A.Zeitschrift fuer Physik B: Condensed Matter (1986), 64 (2), 189-93CODEN: ZPCMDN; ISSN:0722-3277.Metallic, O-deficient compds. in the Ba-La-Cu-O system, with compn. BaxLa5-xCu5O5(3-y) were prepd. in polycryst. form. Samples with x = 1 and 0.75, y >0, annealed below 900° under reducing conditions, consist of 3 phases, one of them a perovskite-like mixed valent Cu compd. Upon cooling, the samples show a linear decrease in resistivity, then an approx. logarithmic increase, interpreted as a beginning of localization. Finally, an abrupt decrease by up to 3 orders of magnitude occurs, reminiscent of the onset of percolative supercond. The highest onset temp. was obsd. in the 30 K range. It is markedly reduced by high current densities. Thus, it results partially from the percolative nature, but possibly also from 2-dimensional superconducting fluctuations of double perovskite layers of one of the phases present.
- 15Kamihara, Y.; Watanabe, T.; Hirano, M.; Hosono, H. Iron-Based Layered Superconductor La[O1-xFx]FeAs (x = 0.05–0.12) with Tc = 26 K J. Am. Chem. Soc. 2008, 130, 3296 DOI: 10.1021/ja800073mGoogle Scholar15Iron-Based Layered Superconductor La[O1-xFx]FeAs (x = 0.05-0.12) with Tc = 26 KKamihara, Yoichi; Watanabe, Takumi; Hirano, Masahiro; Hosono, HideoJournal of the American Chemical Society (2008), 130 (11), 3296-3297CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The authors report that a layered iron-based compd. LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temp. (Tc) exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.
- 16Subedi, A. Electron-phonon superconductivity and charge density wave instability in the layered titanium-based pnictide BaTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 054506 DOI: 10.1103/PhysRevB.87.054506Google ScholarThere is no corresponding record for this reference.
- 17von Rohr, F.; Schilling, A.; Nesper, R.; Baines, C.; Bendele, M. Conventional superconductivity and charge-density-wave ordering in Ba1-xNaxTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 140501 DOI: 10.1103/PhysRevB.88.140501Google ScholarThere is no corresponding record for this reference.
- 18Kitagawa, S.; Ishida, K.; Nakano, K.; Yajima, T.; Kageyama, H. s-wave superconductivity in superconducting BaTi2Sb2O revealed by 121/123Sb-NMR/nuclear quadrupole resonance measurements Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 060510 DOI: 10.1103/PhysRevB.87.060510Google Scholar18s-wave superconductivity in superconducting BaTi2Sb2O revealed by 121/123Sb-NMR/nuclear quadrupole resonance measurementsKitagawa, S.; Ishida, K.; Nakano, K.; Yajima, T.; Kageyama, H.Physical Review B: Condensed Matter and Materials Physics (2013), 87 (6), 060510/1-060510/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We report the 121/123Sb-NMR/NQR (NQR) measurements on the superconductor BaTi2Sb2O with a two-dimensional Ti2O square-net layer formed with Ti3+ (3d1). NQR measurements revealed that the in-plane four-fold symmetry is broken at the Sb site below TA ∼ 40 K, without an internal field appearing at the Sb site. These exclude a spin-d. wave (SDW)/ charge d. wave (CDW) ordering with incommensurate correlations, but can be understood with the commensurate CDW ordering at TA. The spin-lattice relaxation rate 1/T1, measured at the four-fold symmetry breaking site, decreases below superconducting (SC) transition temp. Tc, indicative of the microscopic coexistence of supercond. and the CDW/SDW phase below TA. Furthermore, 1/T1 of 121Sb-NQR shows a coherence peak just below Tc and decreases exponentially at low temps. These results are in sharp contrast with those in cuprate and iron-based superconductors, and strongly suggest that its SC symmetry is classified to an ordinary s-wave state.
- 19Nozaki, Y.; Nakano, K.; Yajima, T.; Kageyama, H.; Frandsen, B.; Liu, L.; Cheung, S.; Goko, T.; Uemura, Y. J.; Munsie, T. S. J.; Medina, T.; Luke, G. M.; Munevar, J.; Nishio-Hamane, D.; Brown, C. M. Muon spin relaxation and electron/neutron diffraction studies of BaTi2(As1-xSbx)2O: Absence of static magnetism and superlattice reflections Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 214506 DOI: 10.1103/PhysRevB.88.214506Google ScholarThere is no corresponding record for this reference.
- 20Gooch, M.; Doan, P.; Tang, Z.; Lorenz, B.; Guloy, A. M.; Chu, P. C. W. Weak coupling BCS-like superconductivity in the pnictide oxide Ba1-xNaxTi2Sb2O (x = 0 and 0.15) Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 064510 DOI: 10.1103/PhysRevB.88.064510Google ScholarThere is no corresponding record for this reference.
- 21Tan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L. Photoemission study of the electronic structure and charge density waves of Na2Ti2Sb2O Sci. Rep. 2015, 5, 9515 DOI: 10.1038/srep09515Google Scholar21Photoemission study of the electronic structure and charge density waves of Na2Ti2Sb2OTan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L.Scientific Reports (2015), 5 (), 9515CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)The electronic structure of Na2Ti2Sb2O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calcn. of Na2Ti2Sb2O in the non-magnetic state, which indicates that there is no magnetic order in Na2Ti2Sb2O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na2Ti2Sb2O. Photon energy dependent ARPES results suggest that the electronic structure of Na2Ti2Sb2O is rather two-dimensional. Moreover, we find a d. wave energy gap forms below the transition temp. and reaches 65 meV at 7 K, indicating that Na2Ti2Sb2O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime.
- 22Nakano, K.; Hongo, K.; Maezono, R. Phonon dispersions and Fermi surfaces nesting explaining the variety of charge ordering in titanium-oxypnictides superconductors Sci. Rep. 2016, 6, 29661 DOI: 10.1038/srep29661Google Scholar22Phonon dispersions and Fermi surfaces nesting explaining the variety of charge ordering in titanium-oxypnictides superconductorsNakano, Kousuke; Hongo, Kenta; Maezono, RyoScientific Reports (2016), 6 (), 29661CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)There has been a puzzle between expts. and theor. predictions on the charge ordering of layered titanium-oxypnictides superconductors. Unconventional mechanisms to explain this discrepancy have been argued so far, even affecting the understanding of supercond. on the compd. We provide a new theor. prediction, by which the discrepancy itself is resolved without any complicated unconventional explanation. Phonon dispersions and changes of nesting vectors in Fermi surfaces are clarified to lead to the variety of superlattice structures even for the common crystal structures when without CDW, including orthorhombic 2 × 2 × 1 one for BaTi2As2O, which has not yet been explained successfully so far, being different from tetragonal √2 × √2 × 1 for BaTi2Sb2O and BaTi2Bi2O. The electronic structure anal. can naturally explain exptl. observations about CDW including most latest ones without any cramped unconventional mechanisms.
- 23Frandsen, B. A.; Bozin, E. S.; Hu, H.; Zhu, Y.; Nozaki, Y.; Kageyama, H.; Uemura, Y. J.; Yin, W.-G.; Billinge, S. J. L. Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors Nat. Commun. 2014, 5, 5761 DOI: 10.1038/ncomms6761Google Scholar23Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductorsFrandsen, Benjamin A.; Bozin, Emil S.; Hu, Hefei; Zhu, Yimei; Nozaki, Yasumasa; Kageyama, Hiroshi; Uemura, Yasutomo J.; Yin, Wei-Guo; Billinge, Simon J. L.Nature Communications (2014), 5 (), 5761CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Understanding the role played by broken-symmetry states such as charge, spin and orbital orders in the mechanism of emergent properties, such as high-temp. supercond., is a major current topic in materials research. That the order may be within one unit cell, such as nematic, was only recently considered theor., but its observation in the iron-pnictide and doped cuprate superconductors places it at the forefront of current research. Here, we show that the recently discovered BaTi2Sb2O superconductor and its parent compd. BaTi2As2O form a symmetry-breaking nematic ground state that can be naturally explained as an intra-unit-cell nematic charge order with d-wave symmetry, pointing to the ubiquity of the phenomenon. These findings, together with the key structural features in these materials being intermediate between the cuprate and iron-pnictide high-temp. superconducting materials, render the titanium oxypnictides an important new material system to understand the nature of nematic order and its relationship to supercond.
- 24Lawler, M. J.; Fujita, K.; Lee, J.; Schmidt, A. R.; Kohsaka, Y.; Kim, C. K.; Eisaki, H.; Uchida, S.; Davis, J. C.; Sethna, J. P.; Kim, E.-A. Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states Nature 2010, 466, 347 DOI: 10.1038/nature09169Google Scholar24Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap statesLawler, M. J.; Fujita, K.; Lee, Jhinhwan; Schmidt, A. R.; Kohsaka, Y.; Kim, Chung Koo; Eisaki, H.; Uchida, S.; Davis, J. C.; Sethna, J. P.; Kim, Eun-AhNature (London, United Kingdom) (2010), 466 (7304), 347-351CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)In the high-transition-temp. (high-Tc) superconductors the pseudogap phase becomes predominant when the d. of doped holes is reduced. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any assocd. order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the detn. of a quant. order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within each CuO2 unit cell. We analyze spectroscopic-imaging scanning tunnelling microscope images of the intra-unit-cell states in underdoped Bi2Sr2CaCu2O8+δ and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90°-rotational symmetry within every CuO2 unit cell.
- 25Kasahara, S.; Shi, H.; Hashimoto, K.; Tonegawa, S.; Mizukami, Y.; Shibauchi, T.; Sugimoto, K.; Fukuda, T.; Terashima, T.; Nevidomskyy, A. H.; Matsuda, Y. Electronic nematicity above the structural and superconducting transition in BaFe2(As1-xPx)2 Nature 2012, 486, 382 DOI: 10.1038/nature11178Google Scholar25Electronic nematicity above the structural and superconducting transition in BaFe2(As1-xPx)2Kasahara, S.; Shi, H. J.; Hashimoto, K.; Tonegawa, S.; Mizukami, Y.; Shibauchi, T.; Sugimoto, K.; Fukuda, T.; Terashima, T.; Nevidomskyy, Andriy H.; Matsuda, Y.Nature (London, United Kingdom) (2012), 486 (7403), 382-385CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Electronic nematicity, a unidirectional self-organized state that breaks the rotational symmetry of the underlying lattice, was obsd. in the Fe pnictide and Cu oxide high-temp. superconductors. Whether nematicity plays an equally important role in these two systems is highly controversial. In Fe pnictides, the nematicity has usually been assocd. with the tetragonal-to-orthorhombic structural transition at temp. Ts. Although recent expts. have provided hints of nematicity, they were performed either in the low-temp. orthorhombic phase or in the tetragonal phase under uniaxial strain, both of which break the 90° rotational C4 symmetry. Therefore, the question remains open whether the nematicity can exist above Ts without an external driving force. Here we report magnetic torque measurements of the isovalent-doping system BaFe2(As1-xPx)2, showing that the nematicity develops well above Ts and, moreover, persists to the non-magnetic superconducting regime, resulting in a phase diagram similar to the pseudogap phase diagram of the Cu oxides. By combining these results with synchrotron x-ray measurements, we identify two distinct temps.-one at T*, signifying a true nematic transition, and the other at Ts (<T*), which we show not to be a true phase transition, but rather what we refer to as a meta-nematic transition', in analogy to the well-known meta-magnetic transition in the theory of magnetism.
- 26Fujita, K.; Hamidian, M. H.; Edkins, S. D.; Kim, C. K.; Kohsaka, Y.; Azuma, M.; Takano, M.; Takagi, H.; Eisaki, H.; Uchida, S.-i.; Allais, A.; Lawler, M. J.; Kim, E.-A.; Sachdev, S.; Davis, J. C. S. Direct phase-sensitive identification of a d-form factor density wave in underdoped cuprates Proc. Natl. Acad. Sci. U. S. A. 2014, 111, E3026 DOI: 10.1073/pnas.1406297111Google ScholarThere is no corresponding record for this reference.
- 27Nakaoka, H.; Yamakawa, Y.; Kontani, H. Theoretical prediction of nematic orbital-ordered state in the Ti oxypnictide superconductor BaTi2(As, Sb)2O Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 245122 DOI: 10.1103/PhysRevB.93.245122Google ScholarThere is no corresponding record for this reference.
- 28Davies, N. R.; Johnson, R. D.; Princep, A. J.; Gannon, L. A.; Ma, J.-Z.; Qian, T.; Richard, P.; Li, H.; Shi, M.; Nowell, H. Coupled commensurate charge density wave and lattice distortion in Na2Ti2Pn2O (Pn = As, Sb) determined by X-ray diffraction and angle-resolved photoemission spectroscopy Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 94, 104515 DOI: 10.1103/PhysRevB.94.104515Google ScholarThere is no corresponding record for this reference.
- 29Kuroki, K.; Usui, H.; Onari, S.; Arita, R.; Aoki, H. Pnictogen height as a possible switch between high-Tc nodeless and low-Tc nodal pairings in the iron-based superconductors Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 224511 DOI: 10.1103/PhysRevB.79.224511Google ScholarThere is no corresponding record for this reference.
- 30Miyake, T.; Nakamura, K.; Arita, R.; Imada, M. Comparison of ab initio low-energy models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe: electron correlation and covalency J. Phys. Soc. Jpn. 2010, 79, 044705 DOI: 10.1143/JPSJ.79.044705Google Scholar30Comparison of ab initio low-energy models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe: electron correlation and covalencyMiyake, Takashi; Nakamura, Kazuma; Arita, Ryotaro; Imada, MasatoshiJournal of the Physical Society of Japan (2010), 79 (4), 044705/1-044705/20CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)Effective low-energy Hamiltonians for several different families of iron-based superconductors are compared after deriving them from the downfolding scheme based on first-principles calcns. Systematic dependences of the derived model parameters on the families are elucidated, many of which are understood from the systematic variation of the covalency between Fe-3d and pnictogen-/chalcogen-p orbitals. First, LaFePO, LaFeAsO (1111), BaFe2As2 (122), LiFeAs (111), FeSe, and FeTe (11) have overall similar band structures near the Fermi level, where the total widths of 10-fold Fe-3d bands are mostly around 4.5 eV. However, the derived effective models of the 10-fold Fe-3d bands (d model) for FeSe and FeTe have substantially larger effective onsite Coulomb interactions U ∼ 4.2 and 3.4 eV, resp., after the screening by electrons on other bands and after averaging over orbitals, as compared to ∼2.5 eV for LaFeAsO. The difference is similar in the effective models contg. p orbitals of As, Se or Te (dp or dpp model), where U ranges from ∼4 eV for the 1111 family to ∼7 eV for the 11 family. The exchange interaction J has a similar tendency. The family dependence of models indicates a wide variation ranging from weak correlation regime (LaFePO) to substantially strong correlation regime (FeSe). The origin of the larger effective interaction in the 11 family is ascribed to smaller spread of the Wannier orbitals generating larger bare interaction, and to fewer screening channels by the other bands. This variation is primarily derived from the distance h between the pnictogen/chalcogen position and the Fe layer: The longer h for the 11 family generates more ionic character of the bonding between iron and anion atoms, while the shorter h for the 1111 family leads to more covalent-bonding character, the larger spread of the Wannier orbitals, and more efficient screening by the anion p orbitals. The screened interaction of the d model is strongly orbital dependent, which is also understood from the Wannier spread. The dp and dpp models show much weaker orbital dependence. The larger h also explains why the 10-fold 3d bands for the 11 family are more entangled with the smearing of the "pseudogap" structure above the Fermi level seen in the 1111 family. While the family-dependent semimetallic splitting of the bands primarily consists of dyz/dzx and dx2-y2 orbitals, the size of the pseudogap structure is controlled by the hybridization between these orbitals and dxy/d3z2-r2: A large hybridization in the 1111 family generates a large "band-insulating"-like pseudogap (hybridization gap), whereas a large h in the 11 family weakens them, resulting in a "half-filled" like bands of orbitals. This may enhance strong correlation effects in analogy with Mott physics and causes the orbital selective crossover in the three orbitals. On the other hand, the geometrical frustration t'/t, inferred from the ratio of the next-nearest transfer r' to the nearest one t of the d model is relatively larger for the 1111 family than the 11 one. The models comprehensively derived here may serve as a firm starting basis of understanding both common and diverse properties of the iron-based superconductors including magnetism and supercond.
- 31Singh, D. J. Electronic structure, disconnected Fermi surfaces and antiferromagnetism in the layered pnictide superconductor NaxBa1-xTi2Sb2O New J. Phys. 2012, 14, 123003 DOI: 10.1088/1367-2630/14/12/123003Google ScholarThere is no corresponding record for this reference.
- 32Yan, X.-W.; Lu, Z.-Y. Layered pnictide-oxide Na2Ti2Pn2O (Pn = As, Sb): a candidate for spin density waves J. Phys.: Condens. Matter 2013, 25, 365501 DOI: 10.1088/0953-8984/25/36/365501Google Scholar32Layered pnictide-oxide Na2Ti2Pn2O (Pn = As, Sb). A candidate for spin density wavesYan, Xun-Wang; Lu, Zhong-YiJournal of Physics: Condensed Matter (2013), 25 (36), 365501, 9 pp.CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)From 1st-principles calcns., we have studied the electronic and magnetic structures of compd. Na2Ti2Pn2O (Pn = As or Sb), whose crystal structure is a bridge between or a combination of those of high-Tc superconducting cuprates and Fe pnictides. We find that in the ground state Na2Ti2As2O is a novel blocked checkerboard antiferromagnetic semiconductor with a small band gap of about 0.15 eV. In contrast, Na2Ti2Sb2O is a bi-collinear antiferromagnetic semimetal, with a small moment of about 0.5 μB around each Ti atom. We show that there is a strong Fermi surface nesting in Na2Ti2Pn2O, and we verify that the blocked checkerboard and bi-collinear antiferromagnetic states both are the spin d. waves induced by the Fermi surface nesting. A tetramer structural distortion is found in company with the formation of a blocked checkerboard antiferromagnetic order, in good agreement with the exptl. obsd. commensurate structural distortion but with space group symmetry retained after the anomaly happens.
- 33Suetin, D.; Ivanovskii, A. Structural, electronic properties, and chemical bonding in quaternary layered titanium pnictide-oxides Na2Ti2Pn2O and BaTi2Pn2O (Pn = As, Sb) from FLAPW-GGA calculations J. Alloys Compd. 2013, 564, 117 DOI: 10.1016/j.jallcom.2013.02.155Google Scholar33Structural, electronic properties, and chemical bonding in quaternary layered titanium pnictide-oxides Na2Ti2Pn2O and BaTi2Pn2O (Pn = As, Sb) from FLAPW-GGA calculationsSuetin, D. V.; Ivanovskii, A. L.Journal of Alloys and Compounds (2013), 564 (), 117-124CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)By the 1st-principles FLAPW-GGA calcns., we have investigated the main trends in structural, electronic properties, and chem. bonding for a series of quaternary Ti pnictide-oxides: Na2Ti2As2O, Na2Ti2Sb2O, BaTi2As2O, and BaTi2Sb2O, which attracted now much attention as parent phases for a novel group of layered Fe-free superconducting materials. Our results cover the optimized lattice parameters and at. positions, electronic bands, Fermi surface topol., total and partial d. of electronic states. Besides, Bader anal. and the charge d. maps are used to discuss the chem. bonding for the examd. materials. We find that the at. substitutions lead to anisotropic deformation of the crystal structure; this effect is related to strong anisotropy of interat. bonds, which are of a mixed (covalent-ionic-metallic) type - in blocks [Ti2Pn2O], whereas the bonding between blocks [Ti2Pn2O] and at. sheets of Na, Ba ions is of an ionic type. The actual effective at. charges differ from the formal ionic charges due to covalency in blocks [Ti2Pn2O]. The near-Fermi electronic bands, which are responsible for metallic-like behavior of these materials and will be involved in the formation of superconducting state, arise mainly from the Ti 3dxy, dx2-y2, and dz2 states of the blocks [Ti2Pn2O], which define also the anisotropic character of conduction happening mainly in these blocks. The differences in the topol. of the multi-sheet Fermi surfaces of these materials are discussed.
- 34Chen, D.; Zhang, T.-T.; Song, Z.-D.; Li, H.; Zhang, W.-L.; Qian, T.; Luo, J.-L.; Shi, Y.-G.; Fang, Z.; Richard, P.; Ding, H. New phase transition in Na2Ti2As2O revealed by Raman scattering Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 140501 DOI: 10.1103/PhysRevB.93.140501Google ScholarThere is no corresponding record for this reference.
- 35
Note that we need to take special care when comparing our calculated geometry with an experimental one due to Davis et al. (28) We found that the atomic positions listed in their Table 1 are incompatible with their superstructure vectors,
,
, and
, described in their main text: (28) (1) If the description in the main text is assumed to be correct, then Na and Sb positions in the superstructure are respectively located unlikely far from their undistorted positions. (2) O is not located at (0.0, 0.0) in their Figure 6a, being inconsistent with their Table 1. Accordingly, we speculate that they again define the superstructure vectors compatible with the atomic positions in their Table 1, which differs from that in their main text. We also found y = 0.0 for As3 in their Table 1 must be a typo and correctly y = 0.25 because As3 should occupy 8j Wyckoff site and its undistorted position is y = 0.5. Assuming our speculation is correct, our optimized geometry parameters agree well with their experimental values.
There is no corresponding record for this reference. - 36Van De Walle, A.; Ceder, G. The effect of lattice vibrations on substitutional alloy thermodynamics Rev. Mod. Phys. 2002, 74, 11 DOI: 10.1103/RevModPhys.74.11Google Scholar36The effect of lattice vibrations on substitutional alloy thermodynamicsVan De Walle, A.; Ceder, G.Reviews of Modern Physics (2002), 74 (1), 11-45CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)A review. A long-standing limitation of first-principles calcns. of substitutional alloy phase diagrams is the difficulty in accounting for lattice vibrations. A survey of the theor. and exptl. literature seeking to quantify the effect of lattice vibrations on phase stability indicates that they can be significant. Typical vibrational entropy differences between phases are of the order of 0.1 to 0.2 kB/atom, which is comparable to the typical values of configurational entropy differences in binary alloys (at most 0.693 kB/atom). This article presents the basic formalism underlying ab initio phase diagram calcns., along with the generalization required to account for lattice vibrations. The authors review the various techniques allowing the theor. calcn. and the exptl. detn. of phonon dispersion curves and related thermodn. quantities, such as vibrational entropy or free energy. A clear picture of the origin of vibrational entropy differences between phases in an alloy system is presented that goes beyond the traditional bond counting and vol. change arguments. Vibrational entropy change can be attributed to the changes in chem. bond stiffness assocd. with the changes in bond length that take place during a phase transformation. This so-called "bond stiffness vs. bond length" interpretation both summarizes the key phenomenon driving vibrational entropy changes and provides a practical tool to model them.
- 37Whangbo, M.-H.; Koo, H.-J.; Villesuzanne, A.; Pouchard, M. Effect of Metal-Oxygen Covalent Bonding on the Competition between Jahn-Teller Distortion and Charge Disproportionation in the Perovskites of High-Spin d4 Metal Ions LaMnO3 and CaFeO3 Inorg. Chem. 2002, 41, 1920 DOI: 10.1021/ic0110427Google ScholarThere is no corresponding record for this reference.
- 38Cammarata, A.; Rondinelli, J. M. Covalent dependence of octahedral rotations in orthorhombic perovskite oxides J. Chem. Phys. 2014, 141, 114704 DOI: 10.1063/1.4895967Google Scholar38Covalent dependence of octahedral rotations in orthorhombic perovskite oxidesCammarata, Antonio; Rondinelli, James M.Journal of Chemical Physics (2014), 141 (11), 114704/1-114704/10CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The compositional dependence of metal-O BO6 octahedral distortions, including bond elongations and rotations, is frequently discussed in the ABO3 perovskite literature; structural distortions alleviate internal stresses driven by under- or over-coordinated bond environments. Here the authors identify the dependence of octahedral rotations from changes in metal-O bond covalency in orthorhombic perovskites. Using d. functional theory the authors formulate a covalency metric, which captures both the real and k-space interactions between the magnitude and sense, i.e., in-phase or out-of-phase, octahedral rotations, to explore the link between the ionic-covalent Fe-O bond and the interoctahedral Fe-O-Fe bond angles in Pbnm ferrates. The authors' survey finds that the covalency of the metal-O bond is correlated with the rotation amplitude: the more covalent the Fe-O bond, the less distorted is the structure and the more important the long-range inter-octahedral (Fe-O-Fe bond angle) interactions were found. Finally, to indirectly tune the B-O bond covalency by A-cation induced BO6 rotations independent of ionic size, facilitating design of targeted bonding interactions in complex perovskites. (c) 2014 American Institute of Physics.
- 39Hughbanks, T.; Hoffmann, R. Chains of trans-edge-sharing molybdenum octahedra: metal-metal bonding in extended systems J. Am. Chem. Soc. 1983, 105, 3528 DOI: 10.1021/ja00349a027Google Scholar39Chains of trans-edge-sharing molybdenum octahedra: metal-metal bonding in extended systemsHughbanks, Timothy; Hoffmann, RoaldJournal of the American Chemical Society (1983), 105 (11), 3528-37CODEN: JACSAT; ISSN:0002-7863.A detailed anal. of bonding in systems with chains of condensed Mo octahedra is given. A 1-dimensional model proves to be applicable over the range of molybdates yet synthesized. The electronic coupling between chains is discussed. Distortions in newly synthesized quaternary systems are seen to result from increased electron count on the Mo chains. The band theoretic explanation of these distortions parallels the treatment of 2nd-order Jahn-Teller distortions.
- 40Dronskowski, R.; Bloechl, P. E. Crystal orbital Hamilton populations (COHP): energy-resolved visualization of chemical bonding in solids based on density-functional calculations J. Phys. Chem. 1993, 97, 8617 DOI: 10.1021/j100135a014Google Scholar40Crystal orbital Hamilton populations (COHP): energy-resolved visualization of chemical bonding in solids based on density-functional calculationsDronskowski, Richard; Bloechl, Peter E.Journal of Physical Chemistry (1993), 97 (33), 8617-24CODEN: JPCHAX; ISSN:0022-3654.After giving a concise overview of the current knowledge in the field of quantum mech. bonding indicators for mols. and solids, the authors show how to obtain energy-resolved visualization of chem. bonding in solids by d.-functional electronic structure calcns. From a band structure energy partitioning scheme, i.e., rewriting the band structure energy as a sum of orbital pair contributions, the authors derive what is to be defined as crystal orbital Hamilton populations (COHP). In particular, a COHP(ε) diagram indicates bonding, nonbonding, and antibonding energy regions within a specified energy range while an energy integral of a COHP gives access to the contribution of an atom or a chem. bond to the distribution of 1-particle energies. A further decompn. into specific AOs or symmetry-adapted linear combinations of AOs (hybrids) can easily be performed by using a projector technique involving unitary transformations. Because of its structural simplicity and the availability of reliable thermodn. data, the authors study the bonding within cryst. silicon (diamond phase) 1st. As a basis set, both bcc. screened and diamond screened at.-centered tight-binding linear muffin-tin orbitals (TB-LMTOs) are used throughout. The shape of COHP vs. energy diagrams and the significance of COHP subcontributions (s-s, sp3-sp3) are analyzed. Specifically, the difference between the COHPs energy integral (1-particle bond energy) and the exptl. bond energy is critically examd. While abs. values for the 1-particle bond energy show a high basis set dependence due to changing on-site (crystal field) COHP terms, the shape of off-site (bonding) COHP functions, elucidating the local bonding principle within an extended structure, remains nearly unaffected.
- 41Grechnev, A.; Ahuja, R.; Eriksson, O. Balanced crystal orbital overlap population—a tool for analysing chemical bonds in solids J. Phys.: Condens. Matter 2003, 15, 7751 DOI: 10.1088/0953-8984/15/45/014Google Scholar41Balanced crystal orbital overlap population-a tool for analysing chemical bonds in solidsGrechnev, Alexei; Ahuja, Rajeev; Eriksson, OlleJournal of Physics: Condensed Matter (2003), 15 (45), 7751-7761CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)A new tool for analyzing theor. the chem. bonding in solids is proposed. A balanced crystal orbital overlap population (BCOOP) is an energy resolved quantity which is pos. for bonding states and neg. for antibonding states, hence enabling a distinction between bonding and antibonding contributions to the chem. bond. Unlike the conventional crystal orbital overlap population (COOP), BCOOP handles correctly the situation of crystal orbitals being nearly linear dependent, which is often the case in the solid state. Also, BCOOP is much less basis set dependent than COOP. A BCOOP implementation within the full-potential linear muffin tin orbital method is presented and illustrated for Si, TiC and Ru. Thus, BCOOP is compared to the COOP and crystal orbital Hamilton population (COHP) for systems with chem. bonds ranging from metallic to covalent character.
- 42
The angle of O–Ti–Pn becomes 87° even at the most stable point for Pn = Sb. The corresponding displacement is 0.125 Å (Figure 9a). In this case, the restoring force between Ti and the nearest O contributing to the direction of the displacement is negligible because cos(87°) is only 0.05.
There is no corresponding record for this reference. - 43Zhang, G.; Glasbrenner, J. K.; Flint, R.; Mazin, I. I.; Fernandes, R. M. Double-stage nematic bond ordering above double stripe magnetism: Application to BaTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2017, 95, 174402 DOI: 10.1103/PhysRevB.95.174402Google ScholarThere is no corresponding record for this reference.
- 44Fan, G.; Zhang, X.; Shi, Y.; Luo, J. Charge density wave transition in Na2Ti2Sb2O probed by 23Na NMR Sci. China: Phys., Mech. Astron. 2013, 56, 2399 DOI: 10.1007/s11433-013-5347-3Google Scholar44Charge density wave transition in Na2Ti2Sb2O probed by 23Na NMRFan, Guo Zhi; Zhang, Xu; Shi, You Guo; Luo, Jian LinScience China: Physics, Mechanics & Astronomy (2013), 56 (12), 2399-2403CODEN: SCPMCL; ISSN:1674-7348. (Springer)Herein we investigated the electronic properties of layered transition-metal oxides Na2Ti2Sb2O by 23Na NMR (NMR) measurement. The resistivity, susceptibility and sp. heat measurements show a phase transition at approx. 114 K (TA). No splitting or broadening in the central line of 23Na NMR spectra is obsd. below and above the transition temp. indicating no internal field being detected. The spin-lattice relaxation rate divided by T (1/T1T) shows a sharp drop at about 110 K which suggests a gap opening behavior. Below the phase transition temp. zone, 1/T1T shows Fermi liq. behavior but with much smaller value indicating the loss of large part of electronic d. of states (DOS) because of the gap. No signature of the enhancement of spin fluctuations or magnetic order is found with the decreasing temp. These results suggest a commensurate charge-d.-wave (CDW) phase transition occurring.
- 45Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple Phys. Rev. Lett. 1996, 77, 3865 DOI: 10.1103/PhysRevLett.77.3865Google Scholar45Generalized gradient approximation made simplePerdew, John P.; Burke, Kieron; Ernzerhof, MatthiasPhysical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
- 46Giannozzi, P. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials J. Phys.: Condens. Matter 2009, 21, 395502 DOI: 10.1088/0953-8984/21/39/395502Google Scholar46QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materialsGiannozzi Paolo; Baroni Stefano; Bonini Nicola; Calandra Matteo; Car Roberto; Cavazzoni Carlo; Ceresoli Davide; Chiarotti Guido L; Cococcioni Matteo; Dabo Ismaila; Dal Corso Andrea; de Gironcoli Stefano; Fabris Stefano; Fratesi Guido; Gebauer Ralph; Gerstmann Uwe; Gougoussis Christos; Kokalj Anton; Lazzeri Michele; Martin-Samos Layla; Marzari Nicola; Mauri Francesco; Mazzarello Riccardo; Paolini Stefano; Pasquarello Alfredo; Paulatto Lorenzo; Sbraccia Carlo; Scandolo Sandro; Sclauzero Gabriele; Seitsonen Ari P; Smogunov Alexander; Umari Paolo; Wentzcovitch Renata MJournal of physics. Condensed matter : an Institute of Physics journal (2009), 21 (39), 395502 ISSN:.QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.
- 47Blöchl, P. E. Projector augmented-wave method Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953 DOI: 10.1103/PhysRevB.50.17953Google Scholar47Projector augmented-wave methodBlochlPhysical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.There is no expanded citation for this reference.
- 48Jollet, F.; Torrent, M.; Holzwarth, N. Generation of Projector Augmented-Wave atomic data: A 71 element validated table in the XML format Comput. Phys. Commun. 2014, 185, 1246 DOI: 10.1016/j.cpc.2013.12.023Google Scholar48Generation of Projector Augmented-Wave atomic data: A 71 element validated table in the XML formatJollet, Francois; Torrent, Marc; Holzwarth, NatalieComputer Physics Communications (2014), 185 (4), 1246-1254CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)In the Projector Augmented Wave (PAW) method developed by Bloechl (1994), a PAW data file is needed for each element, taking the role of the pseudopotential file used with the norm-conserving or ultrasoft formalisms. In this paper, we review methods for generating PAW data files and for evaluating their accuracy, transferability, and numerical efficiency in simulations of bulk solids. We have developed a new set of PAW at. data files for most of the stable elements in the periodic table. These files are provided in a std. XML format for use in any PAW electronic structure code. The new dataset performs well as measured by the "Δ" evaluation criterion introduced by Lejaeghere et al. (2014), and also performs well in a modified evaluation scheme proposed in the present paper.
- 49Kucukbenli, E.; Monni, M.; Adetunji, B.; Ge, X.; Adebayo, G.; Marzari, N.; de Gironcoli, S.; Corso, A. D. Projector augmented-wave and all-electron calculations across the periodic table: a comparison of structural and energetic properties. 2014, arXiv:cond-mat.mtrl-sci/1404.3015. arXiv.org e-Print archive. https://arxiv.org/abs/1404.3015 (accessed July 6, 2017).Google ScholarThere is no corresponding record for this reference.
- 50Baroni, S.; de Gironcoli, S.; Dal Corso, A.; Giannozzi, P. Phonons and related crystal properties from density-functional perturbation theory Rev. Mod. Phys. 2001, 73, 515 DOI: 10.1103/RevModPhys.73.515Google Scholar50Phonons and related crystal properties from density-functional perturbation theoryBaroni, Stefano; De Gironcoli, Stefano; Dal Corso, Andrea; Giannozzi, PaoloReviews of Modern Physics (2001), 73 (2), 515-562CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)This article reviews with many refs. the current status of lattice-dynamical calcns. in crystals, using d.-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calcn. of the response to macroscopic elec. fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodol. is demonstrated with a no. of applications existing in the literature.
- 51Momma, K.; Izumi, F. VESTA3 for three-dimensional visualization of crystal, volumetric and morphology data J. Appl. Crystallogr. 2011, 44, 1272 DOI: 10.1107/S0021889811038970Google Scholar51VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology dataMomma, Koichi; Izumi, FujioJournal of Applied Crystallography (2011), 44 (6), 1272-1276CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)VESTA is a 3D visualization system for crystallog. studies and electronic state calcns. It was upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphpol. of crysals; superimposing multiple structural models, volumetric data and crystal faces; calcn. of electron and nuclear densities from structure parameters; calcn. of Patterson functions from the structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels, detn. of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex mols. and cage-like structures; undo and redo is graphical user interface operations; and significant performance improvements in rendering isosurfaces and calcg. slices.
- 52Kokalj, A. XCrySDen a new program for displaying crystalline structures and electron densities J. Mol. Graphics Modell. 1999, 17, 176 DOI: 10.1016/S1093-3263(99)00028-5Google Scholar52XCrySDen--a new program for displaying crystalline structures and electron densitiesKokalj AJournal of molecular graphics & modelling (1999), 17 (3-4), 176-9, 215-6 ISSN:1093-3263.XCrySDen is a molecular and crystalline-structure visualization program, but its main function is as a property analyzer program. It can run on most UNIX platforms, without any special hardware or software requirements. Special efforts were made to allow for appropriate display of 3D isosurfaces and 2D contours, which can be superimposed on crystalline structure and interactively rotated and manipulated. XCrySDen is also a graphical user interface for the CRYSTAL95/98 (Saunders, V. R., et al. CRYSTAL98--User's Manual. University of Torino, Turin, Italy, 1999) ab initio program and a visualization system for the WIEN97 (Blaha, P., et al. Comput. Phys. Commun. 1990, 59, 399) ab initio program. In this article the program functions are presented with a short description of the algorithms.
- 53Marzari, N.; Vanderbilt, D.; De Vita, A.; Payne, M. C. Thermal Contraction and Disordering of the Al(110) Surface Phys. Rev. Lett. 1999, 82, 3296 DOI: 10.1103/PhysRevLett.82.3296Google Scholar53Thermal Contraction and Disordering of the Al(110) SurfaceMarzari, Nicola; Vanderbilt, David; De Vita, Alessandro; Payne, M. C.Physical Review Letters (1999), 82 (16), 3296-3299CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Al(110) has been studied for temps. up to 900 K via ensemble d.-functional mol. dynamics. The strong anharmonicity displayed by this surface results in a neg. coeff. of thermal expansion, where the first interlayer distance decreases with increasing temp. Very shallow channels of oscillation for the second-layer atoms in the direction perpendicular to the surface support this anomalous contraction, and provide a novel mechanism for the formation of adatom-vacancy pairs, preliminary to the disordering and premelting transition. Such characteristic behavior originates in the free-electron-gas bonding at a loosely packed surface.
- 54Ozawa, T. C.; Pantoja, R.; Axtell, E. A.; Kauzlarich, S. M.; Greedan, J. E.; Bieringer, M.; Richardson, J. W. Powder Neutron Diffraction Studies of Na2Ti2Sb2O and Its Structure Property Relationships J. Solid State Chem. 2000, 153, 275– 281 DOI: 10.1006/jssc.2000.8758Google Scholar54Powder neutron diffraction studies of Na2Ti2Sb2O and its structure-property relationshipsOzawa, Tadashi C.; Pantoja, Rigo; Axtell, Enos A., III; Kauzlarich, Susan M.; Greedan, John E.; Bieringer, Mario; Richardson, James W., Jr.Journal of Solid State Chemistry (2000), 153 (2), 275-281CODEN: JSSCBI; ISSN:0022-4596. (Academic Press)The structure of Na2Ti2Sb2O was studied by temp.-dependent powder neutron diffraction. Na2Ti2Sb2O crystallizes in I4/mmm symmetry. The structure of this phase can be viewed as an anti-K2NiF4 type where Ti3+ ion is located between two O atoms forming a square-planar lattice. Powder neutron diffraction studies of Na2Ti2Sb2O indicate that this compd. has a structural distortion in the [Ti2Sb2O]2- layer at T ≈ 120 K. This transition corresponds well to the previously reported anomalous transition temp. of the magnetic susceptibility and electronic resistivity. Several models to explain the data are presented and discussed. (c) 2000 Academic Press.
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Abstract
Figure 1
Figure 1. Crystal structure of Na2Ti2Pn2O (Pn = As and Sb). The space group is I4/mmm.
Figure 2
Figure 2. Electronic band structures for undistorted Na2Ti2Pn2O structure ((a) Pn = As, (b) Pn = Sb). The Fermi energy is set to 0 eV.
Figure 3
Figure 3. Phonon dispersions and phonon DOS for undistorted (I4/mmm) Na2Ti2Pn2O (Pn = (a) As, (b) Sb). The red cross marks in (b) represent the frequencies with spin–orbit coupling.
Figure 4
Figure 4. In-plane superstructures obtained by our calculations for Pn = (a) As and (b) Sb, and (c) the observed in-plane superstructure for Pn = Sb. (28) Pn is located above and below the Ti2O plane. Solid lines represent the original unit cells for I4/mmm. Thin dash lines represent the unit cells for 2 × 2 superstructures. Solid dash lines represent redefined unit cells for distorted superstructures. The conventional lattice vectors of the superstructure for (a) Pn = As (C2/m) are redefined as
,
, and
, those for (b) Pn = Sb (Cmce) are redefined as
,
, and
, and those for (c) Pn = Sb (Cmcm) are redefined as
,
, and
, where
,
, and
are conventional lattice vectors of the undistorted structures.
Figure 5
Figure 5. 3D superstructures obtained from our calculations for Pn = (a) As (C2/m) and (b) Sb (Cmce).
Figure 6
Figure 6. Phonon dispersions for Na2Ti2Sb2O superstructure (Cmce).
Figure 7
Figure 7. Partial density of states and center of masses of Na2Ti2Pn2O (a) Pn = As, (b) Pn = Sb.
Figure 8
Figure 8. Electron densities of Na2Ti2Pn2O (a) Pn = As, (b) Pn = Sb along Ti–Pn bonds. The electron densities are plotted in the same range (0.03–0.07 electron/bohr3), and the aspects are consistent with each crystal structure.
Figure 9
Figure 9. (a) Change in potential energy accompanying the displacement of Ti atoms according to the phonon showing the imaginary (lowest) frequency at X point in Pn = Sb (As). The horizontal axis corresponds to the magnitude of the displacement from the original positon. (b) Two-dimensional image of the displacement parttern of Ti atoms. (c) Three-dimensional image of the displacement parttern of the Ti atom enclosed in a red broken line in (b).
Figure 10
Figure 10. Primitive Brillouin zones (a) for undistorted Na2Ti2Pn2O structure (I4/mmm) and (b) for Na2Ti2Sb2O superstructure (Cmce).
References
This article references 54 other publications.
- 1Axtell, E. A.; Ozawa, T.; Kauzlarich, S. M.; Singh, R. R. Phase Transition and Spin-gap Behavior in a Layered Tetragonal Pnictide Oxide J. Solid State Chem. 1997, 134, 423 DOI: 10.1006/jssc.1997.77151Phase transition and spin-gap behavior in a layered tetragonal pnictide oxideAxtell, E. A., III; Ozawa, Tadashi; Kauzlarich, Susan M.; Singh, Rajiv R. P.Journal of Solid State Chemistry (1997), 134 (2), 423-426CODEN: JSSCBI; ISSN:0022-4596. (Academic Press)Spin-gap behavior was obsd. for the 1st time in the layered tetragonal compd. Na2Ti2Sb2O. Na2Ti2Sb2O shows a sharp discontinuity in magnetic susceptibility at 150 K, reminiscent of behavior obsd. in the spin-Peierls compd. CuGeO3. Na2Ti2Sb2O also shows a discontinuity in temp.-dependent resistivity at the magnetic transition and metallic behavior for all other temps., 5.7 mΩ cm at room temp. Ti-Sb-Ti superexchange probably is favored over Ti-O-Ti superexchange, based on the high-temp. magnetic susceptibility data and on the identity of the magnetic orbitals.
- 2Ozawa, T. C.; Kauzlarich, S. M.; Bieringer, M.; Greedan, J. E. Possible Charge-Density-Wave/Spin-Density-Wave in the Layered PnictideOxides:Na2Ti2Pn2O (Pn = As, Sb) Chem. Mater. 2001, 13, 1804 DOI: 10.1021/cm010009fThere is no corresponding record for this reference.
- 3Liu, R.; Song, Y.; Li, Q.; Ying, J.; Yan, Y.; He, Y.; Chen, X. Structure and Physical Properties of the Layered Pnictide-Oxides:(SrF)2Ti2Pn2O (Pn = As, Sb) and (SmO)2Ti2Sb2O Chem. Mater. 2010, 22, 1503 DOI: 10.1021/cm9027258There is no corresponding record for this reference.
- 4Wang, X. F.; Yan, Y. J.; Ying, J. J.; Li, Q. J.; Zhang, M.; Xu, N.; Chen, X. H. Structure and physical properties for a new layered pnictide-oxide: BaTi2As2O J. Phys.: Condens. Matter 2010, 22, 075702 DOI: 10.1088/0953-8984/22/7/0757024Structure and physical properties for a new layered pnictide-oxide: BaTi2As2OWang, X. F.; Yan, Y. J.; Ying, J. J.; Li, Q. J.; Zhang, M.; Xu, N.; Chen, X. H.Journal of Physics: Condensed Matter (2010), 22 (7), 075702/1-075702/5CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)A layered pnictide-oxide BaTi2As2O have been prepd. and characterized. It shares similar characteristics with Na2Ti2Sb2O. The crystal has a layered structure with a tetragonal P4/nmm group (a = 4.047(3), c = 7.275(4) Å). The resistivity shows an anomaly at 200 K, which should be ascribed to an SDW or structural transition. The SDW or structural transition is confirmed by magnetic susceptibility and heat capacity measurements. These properties are very similar to those obsd. in parent compds. of high-Tc iron-based pnictide superconductors where the supercond. shows up when the anomaly due to the SDW or structural transition is suppressed. Li+ doping significantly suppresses the anomaly, but no supercond. emerges.
- 5Doan, P.; Gooch, M.; Tang, Z.; Lorenz, B.; Moeller, A.; Tapp, J.; Chu, P. C. W.; Guloy, A. M. Ba1–xNaxTi2Sb2O (0.0 ≤ x ≤ 0.33) A Layered Titanium-Based Pnictide Oxide Superconductor J. Am. Chem. Soc. 2012, 134, 16520 DOI: 10.1021/ja3078889There is no corresponding record for this reference.
- 6Yajima, T.; Nakano, K.; Takeiri, F.; Ono, T.; Hosokoshi, Y.; Matsushita, Y.; Hester, J.; Kobayashi, Y.; Kageyama, H. Superconductivity in BaTi2Sb2O with a d1 Square Lattice J. Phys. Soc. Jpn. 2012, 81, 103706 DOI: 10.1143/JPSJ.81.1037066Superconductivity in BaTi2Sb2O with a d1 square latticeYajima, Takeshi; Nakano, Kousuke; Takeiri, Fumitaka; Ono, Toshio; Hosokoshi, Yuko; Matsushita, Yoshitaka; Hester, James; Kobayashi, Yoji; Kageyama, HiroshiJournal of the Physical Society of Japan (2012), 81 (10), 103706/1-103706/4CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)We prepd. a new two-dimensional oxyantimonide, BaTi2Sb2O, which shows a superconducting transition at 1.2 K, representing the first supercond. in a system with Ti3+ (d1) in a square lattice. The TiO2Sb4 mixed anionic coordination stabilizes a unique half-filled Ti dxy orbital configuration in Ti2O plane, which is analogous to Cu2+ (d9) in the high-Tc superconductors. A charge d. wave (CDW)- or spin d. wave (SDW)-like anomaly appears at 50 K, which is significantly reduced compared with 200 K for the isostructural and non-superconducting BaTi2As2O.
- 7Yajima, T.; Nakano, K.; Takeiri, F.; Hester, J.; Yamamoto, T.; Kobayashi, Y.; Tsuji, N.; Kim, J.; Fujiwara, A.; Kageyama, H. Synthesis and Physical Properties of the New Oxybismuthides BaTi2Bi2O and (SrF)2Ti2Bi2O with a d1 Square Net J. Phys. Soc. Jpn. 2013, 82, 013703 DOI: 10.7566/JPSJ.82.0137037Synthesis and physical properties of the new oxybismuthides BaTi2Bi2O and (SrF)2Ti2Bi2O with a d1 square netYajima, Takeshi; Nakano, Kousuke; Takeiri, Fumitaka; Hester, James; Yamamoto, Takafumi; Kobayashi, Yoji; Tsuji, Naruki; Kim, Jungeun; Fujiwara, Akihiko; Kageyama, HiroshiJournal of the Physical Society of Japan (2013), 82 (1), 013703/1-013703/4CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)We have recently reported the d1 square-lattice compd. BaTi2Sb2O, which shows supercond. at Tc = 1.2 K coexisting with a charge- or spin-d. wave (CDW/SDW) state. Here, we successfully prepd. two new oxybismuthides, BaTi2Bi2O and (SrF)2Ti2Bi2O, as the first Pn = Bi compds. in the ATi2Pn2O family. The CDW/SDW state disappeared for both compds., presumably owing to the considerable interaction between the Ti-3d and Bi-6s orbitals. The complete suppression of the CDW/SDW instability resulted in an enhanced Tc of 4.6 K for BaTi2Bi2O. However, (SrF)2Ti2Bi2O exhibits no supercond., suggesting the importance of the interlayer interaction for supercond.
- 8Yajima, T.; Nakano, K.; Takeiri, F.; Nozaki, Y.; Kobayashi, Y.; Kageyama, H. Two Superconducting Phases in the Isovalent Solid Solutions BaTi2Pn2O (Pn = As, Sb, and Bi) J. Phys. Soc. Jpn. 2013, 82, 033705 DOI: 10.7566/JPSJ.82.0337058Two superconducting phases in the isovalent solid solutions BaTi2Pn2O (Pn = As, Sb, and Bi)Yajima, Takeshi; Nakano, Kousuke; Takeiri, Fumitaka; Nozaki, Yasumasa; Kobayashi, Yoji; Kageyama, HiroshiJournal of the Physical Society of Japan (2013), 82 (3), 033705/1-033705/4CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)We have recently reported two superconductors with the d1 square lattice, BaTi2Sb2O (Tc = 1.2 K) and BaTi2Bi2O (Tc = 4.6 K). In order to find a clue behind the supercond. of these materials, we synthesized isovalent solid solns. of BaTi2(As1-xSbx)2O and BaTi2(Sb1-yBiy)2O. Despite Vegard's law behavior in cell consts., a two-dome structure in Tc was obsd. with two distinct superconducting phases ("0.9 ≤ x; y ≤ 0.3" and "0.6 ≤ y ≤ 1") sepd. by a metallic phase. This result implies a multiband nature at the Fermi surface in BaTi2Pn2O.
- 9Zhai, H.-F.; Jiao, W.-H.; Sun, Y.-L.; Bao, J.-K.; Jiang, H.; Yang, X.-J.; Tang, Z.-T.; Tao, Q.; Xu, X.-F.; Li, Y.-K.; Cao, C.; Dai, J.-H.; Xu, Z.-A.; Cao, G.-H. Superconductivity, charge- or spin-density wave, and metal-nonmetal transition in BaTi2(Sb1-xBix)2O Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 100502 DOI: 10.1103/PhysRevB.87.100502There is no corresponding record for this reference.
- 10Nakano, K.; Yajima, T.; Takeiri, F.; Green, M. A.; Hester, J.; Kobayashi, Y.; Kageyama, H. Tc Enhancement by Aliovalent Anionic Substitution in Superconducting BaTi2(Sb1–xSnx)2O J. Phys. Soc. Jpn. 2013, 82, 074707 DOI: 10.7566/JPSJ.82.07470710Tc enhancement by aliovalent anionic substitution in superconducting BaTi2(Sb1-xSnx)2ONakano, Kousuke; Yajima, Takeshi; Takeiri, Fumitaka; Green, Mark A.; Hester, James; Kobayashi, Yoji; Kageyama, HiroshiJournal of the Physical Society of Japan (2013), 82 (7), 074707/1-074707/5CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)BaTi2Sb2O is a Tc = 1.2 K superconductor with a d1 square lattice, and isovalent Bi substitution for Sb can increase its Tc to 4.6 K (BaTi2Bi2O), accompanied by the complete suppression of charge d. wave (CDW) or spin d. wave (SDW) transition. In the present study, we demonstrate that aliovalent Sn substitution (hole doping) also increases Tc up to 2.5 K for BaTi2(Sb0.7Sn0.3)2O, while suppressing CDW/SDW transition only slightly. The overall electronic phase diagram of BaTi2(Sb,Sn)2O is qual. similar to that of cation-substituted (hole-doped) (Ba,Na)Ti2Sb2O, but quant. differences such as in Tc are obsd., which is discussed in terms of Ti-Pn hybridization and chem. disorder.
- 11Pachmayr, U.; Johrendt, D. Superconductivity in Ba1-xKxTi2Sb2O (0 ≤ x ≤ 1) controlled by the layer charge Solid State Sci. 2014, 28, 31 DOI: 10.1016/j.solidstatesciences.2013.12.00511Superconductivity in Ba1-xKxTi2Sb2O (0 ≤ x ≤ 1) controlled by the layer chargePachmayr, Ursula; Johrendt, DirkSolid State Sciences (2014), 28 (), 31-34CODEN: SSSCFJ; ISSN:1293-2558. (Elsevier Masson SAS)The solid soln. of antimonide-oxides Ba1-xKxTi2Sb2O (0 ≤ x ≤ 1) has been synthesized by solid-state reactions and characterized by X-ray powder diffraction (CeCr2Si2C-type structure; P4/mmm, Z = 1). The crystal structure consists of Ti2Sb2O-layers that are stacked with layers of barium atoms along the c-axis. BaTi2Sb2O is a known superconductor with a crit. temp. (Tc) of 1.2 K. Substitution of barium through potassium raises Tc up to 6.1 K at 12% potassium, while no supercond. emerges with concns. higher than 20%. Anomalies in elec. transport and magnetic susceptibility indicate charge d. wave (CDW) instabilities. The CDW transition temps. (Ta) decrease from 50 K in the parent compd. to 28 K at 10% potassium substitution. No CDW transition was detected at higher concns., and no evidence for a redn. of the lattice symmetry below Ta was found. The lattice parameters vary linearly while the unit cell vol. increases with higher potassium concns. The phase diagrams Tc(x) and Ta(x) of Ba1-xKxTi2Sb2O are remarkably similar to the known series Ba1-xNaxTi2Sb2O (0 ≤ x ≤ 0.33) in spite of the reverse vol. effect. From this we conclude that the charge and not the vol. dets. the phase diagrams of these superconducting antimonide-oxides.
- 12von Rohr, F.; Nesper, R.; Schilling, A. Superconductivity in rubidium-substituted Ba1-xRbxTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 89, 094505 DOI: 10.1103/PhysRevB.89.09450512Superconductivity in rubidium-substituted Ba1-xRbxTi2Sb2Ovon Rohr, Fabian; Nesper, Reinhard; Schilling, AndreasPhysical Review B: Condensed Matter and Materials Physics (2014), 89 (9), 094505/1-094505/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We report on the synthesis and the phys. properties of Ba1-xRbxTi2Sb2O (x ≤ 0.4) by x-ray diffraction, superconducting quantum interference device magnetometry, resistivity, and specific-heat measurements. Upon hole doping by substituting Ba with Rb, we find supercond. with a max. Tc = 5.4 K. Simultaneously, the charge-d.-wave transition temp. is strongly reduced from TCDW ≈ 55 K in the parent compd. BaTi2Sb2O and seems to be suppressed for x ≥ 0.2. The bulk character of the superconducting state for the optimally doped sample (x = 0.2) is confirmed by the occurrence of a well developed discontinuity in the sp. heat at Tc, with ΔC/Tc ≈ 22 mJ/mol K2, as well as a large Meissner-shielding fraction of ≈40%. The isotropically averaged lower and upper crit. fields of the optimally doped sample (x = 0.2) are estd. to μ0Hc,1(0) ≈ 3.8 mT and μ0Hc,2(0) ≈ 2.3 T, resp., indicating that these compds. are strongly type-II superconductors.
- 13Ji, Q.; Ma, Y.; Hu, K.; Gao, B.; Mu, G.; Li, W.; Hu, T.; Zhang, G.; Zhao, Q.; Zhang, H.; Huang, F.; Xie, X. Synthesis, Structural, and Transport Properties of Cr-Doped BaTi2As2O Inorg. Chem. 2014, 53, 13089 DOI: 10.1021/ic502192hThere is no corresponding record for this reference.
- 14Bednorz, J.; Müller, K. Possible high Tc superconductivity in the Ba-La-Cu-O system Z. Phys. B: Condens. Matter 1986, 64, 189 DOI: 10.1007/BF0130370114Possible high Tc superconductivity in the barium-lanthanum-copper-oxygen systemBednorz, J. G.; Mueller, K. A.Zeitschrift fuer Physik B: Condensed Matter (1986), 64 (2), 189-93CODEN: ZPCMDN; ISSN:0722-3277.Metallic, O-deficient compds. in the Ba-La-Cu-O system, with compn. BaxLa5-xCu5O5(3-y) were prepd. in polycryst. form. Samples with x = 1 and 0.75, y >0, annealed below 900° under reducing conditions, consist of 3 phases, one of them a perovskite-like mixed valent Cu compd. Upon cooling, the samples show a linear decrease in resistivity, then an approx. logarithmic increase, interpreted as a beginning of localization. Finally, an abrupt decrease by up to 3 orders of magnitude occurs, reminiscent of the onset of percolative supercond. The highest onset temp. was obsd. in the 30 K range. It is markedly reduced by high current densities. Thus, it results partially from the percolative nature, but possibly also from 2-dimensional superconducting fluctuations of double perovskite layers of one of the phases present.
- 15Kamihara, Y.; Watanabe, T.; Hirano, M.; Hosono, H. Iron-Based Layered Superconductor La[O1-xFx]FeAs (x = 0.05–0.12) with Tc = 26 K J. Am. Chem. Soc. 2008, 130, 3296 DOI: 10.1021/ja800073m15Iron-Based Layered Superconductor La[O1-xFx]FeAs (x = 0.05-0.12) with Tc = 26 KKamihara, Yoichi; Watanabe, Takumi; Hirano, Masahiro; Hosono, HideoJournal of the American Chemical Society (2008), 130 (11), 3296-3297CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)The authors report that a layered iron-based compd. LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temp. (Tc) exhibits a trapezoid shape dependence on the F- content, with the highest Tc of ∼26 K at ∼11 atom %.
- 16Subedi, A. Electron-phonon superconductivity and charge density wave instability in the layered titanium-based pnictide BaTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 054506 DOI: 10.1103/PhysRevB.87.054506There is no corresponding record for this reference.
- 17von Rohr, F.; Schilling, A.; Nesper, R.; Baines, C.; Bendele, M. Conventional superconductivity and charge-density-wave ordering in Ba1-xNaxTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 140501 DOI: 10.1103/PhysRevB.88.140501There is no corresponding record for this reference.
- 18Kitagawa, S.; Ishida, K.; Nakano, K.; Yajima, T.; Kageyama, H. s-wave superconductivity in superconducting BaTi2Sb2O revealed by 121/123Sb-NMR/nuclear quadrupole resonance measurements Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 060510 DOI: 10.1103/PhysRevB.87.06051018s-wave superconductivity in superconducting BaTi2Sb2O revealed by 121/123Sb-NMR/nuclear quadrupole resonance measurementsKitagawa, S.; Ishida, K.; Nakano, K.; Yajima, T.; Kageyama, H.Physical Review B: Condensed Matter and Materials Physics (2013), 87 (6), 060510/1-060510/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We report the 121/123Sb-NMR/NQR (NQR) measurements on the superconductor BaTi2Sb2O with a two-dimensional Ti2O square-net layer formed with Ti3+ (3d1). NQR measurements revealed that the in-plane four-fold symmetry is broken at the Sb site below TA ∼ 40 K, without an internal field appearing at the Sb site. These exclude a spin-d. wave (SDW)/ charge d. wave (CDW) ordering with incommensurate correlations, but can be understood with the commensurate CDW ordering at TA. The spin-lattice relaxation rate 1/T1, measured at the four-fold symmetry breaking site, decreases below superconducting (SC) transition temp. Tc, indicative of the microscopic coexistence of supercond. and the CDW/SDW phase below TA. Furthermore, 1/T1 of 121Sb-NQR shows a coherence peak just below Tc and decreases exponentially at low temps. These results are in sharp contrast with those in cuprate and iron-based superconductors, and strongly suggest that its SC symmetry is classified to an ordinary s-wave state.
- 19Nozaki, Y.; Nakano, K.; Yajima, T.; Kageyama, H.; Frandsen, B.; Liu, L.; Cheung, S.; Goko, T.; Uemura, Y. J.; Munsie, T. S. J.; Medina, T.; Luke, G. M.; Munevar, J.; Nishio-Hamane, D.; Brown, C. M. Muon spin relaxation and electron/neutron diffraction studies of BaTi2(As1-xSbx)2O: Absence of static magnetism and superlattice reflections Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 214506 DOI: 10.1103/PhysRevB.88.214506There is no corresponding record for this reference.
- 20Gooch, M.; Doan, P.; Tang, Z.; Lorenz, B.; Guloy, A. M.; Chu, P. C. W. Weak coupling BCS-like superconductivity in the pnictide oxide Ba1-xNaxTi2Sb2O (x = 0 and 0.15) Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 064510 DOI: 10.1103/PhysRevB.88.064510There is no corresponding record for this reference.
- 21Tan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L. Photoemission study of the electronic structure and charge density waves of Na2Ti2Sb2O Sci. Rep. 2015, 5, 9515 DOI: 10.1038/srep0951521Photoemission study of the electronic structure and charge density waves of Na2Ti2Sb2OTan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L.Scientific Reports (2015), 5 (), 9515CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)The electronic structure of Na2Ti2Sb2O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calcn. of Na2Ti2Sb2O in the non-magnetic state, which indicates that there is no magnetic order in Na2Ti2Sb2O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na2Ti2Sb2O. Photon energy dependent ARPES results suggest that the electronic structure of Na2Ti2Sb2O is rather two-dimensional. Moreover, we find a d. wave energy gap forms below the transition temp. and reaches 65 meV at 7 K, indicating that Na2Ti2Sb2O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime.
- 22Nakano, K.; Hongo, K.; Maezono, R. Phonon dispersions and Fermi surfaces nesting explaining the variety of charge ordering in titanium-oxypnictides superconductors Sci. Rep. 2016, 6, 29661 DOI: 10.1038/srep2966122Phonon dispersions and Fermi surfaces nesting explaining the variety of charge ordering in titanium-oxypnictides superconductorsNakano, Kousuke; Hongo, Kenta; Maezono, RyoScientific Reports (2016), 6 (), 29661CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)There has been a puzzle between expts. and theor. predictions on the charge ordering of layered titanium-oxypnictides superconductors. Unconventional mechanisms to explain this discrepancy have been argued so far, even affecting the understanding of supercond. on the compd. We provide a new theor. prediction, by which the discrepancy itself is resolved without any complicated unconventional explanation. Phonon dispersions and changes of nesting vectors in Fermi surfaces are clarified to lead to the variety of superlattice structures even for the common crystal structures when without CDW, including orthorhombic 2 × 2 × 1 one for BaTi2As2O, which has not yet been explained successfully so far, being different from tetragonal √2 × √2 × 1 for BaTi2Sb2O and BaTi2Bi2O. The electronic structure anal. can naturally explain exptl. observations about CDW including most latest ones without any cramped unconventional mechanisms.
- 23Frandsen, B. A.; Bozin, E. S.; Hu, H.; Zhu, Y.; Nozaki, Y.; Kageyama, H.; Uemura, Y. J.; Yin, W.-G.; Billinge, S. J. L. Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors Nat. Commun. 2014, 5, 5761 DOI: 10.1038/ncomms676123Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductorsFrandsen, Benjamin A.; Bozin, Emil S.; Hu, Hefei; Zhu, Yimei; Nozaki, Yasumasa; Kageyama, Hiroshi; Uemura, Yasutomo J.; Yin, Wei-Guo; Billinge, Simon J. L.Nature Communications (2014), 5 (), 5761CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Understanding the role played by broken-symmetry states such as charge, spin and orbital orders in the mechanism of emergent properties, such as high-temp. supercond., is a major current topic in materials research. That the order may be within one unit cell, such as nematic, was only recently considered theor., but its observation in the iron-pnictide and doped cuprate superconductors places it at the forefront of current research. Here, we show that the recently discovered BaTi2Sb2O superconductor and its parent compd. BaTi2As2O form a symmetry-breaking nematic ground state that can be naturally explained as an intra-unit-cell nematic charge order with d-wave symmetry, pointing to the ubiquity of the phenomenon. These findings, together with the key structural features in these materials being intermediate between the cuprate and iron-pnictide high-temp. superconducting materials, render the titanium oxypnictides an important new material system to understand the nature of nematic order and its relationship to supercond.
- 24Lawler, M. J.; Fujita, K.; Lee, J.; Schmidt, A. R.; Kohsaka, Y.; Kim, C. K.; Eisaki, H.; Uchida, S.; Davis, J. C.; Sethna, J. P.; Kim, E.-A. Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap states Nature 2010, 466, 347 DOI: 10.1038/nature0916924Intra-unit-cell electronic nematicity of the high-Tc copper-oxide pseudogap statesLawler, M. J.; Fujita, K.; Lee, Jhinhwan; Schmidt, A. R.; Kohsaka, Y.; Kim, Chung Koo; Eisaki, H.; Uchida, S.; Davis, J. C.; Sethna, J. P.; Kim, Eun-AhNature (London, United Kingdom) (2010), 466 (7304), 347-351CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)In the high-transition-temp. (high-Tc) superconductors the pseudogap phase becomes predominant when the d. of doped holes is reduced. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any assocd. order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the detn. of a quant. order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within each CuO2 unit cell. We analyze spectroscopic-imaging scanning tunnelling microscope images of the intra-unit-cell states in underdoped Bi2Sr2CaCu2O8+δ and, using two independent evaluation techniques, find evidence for electronic nematicity of the states close to the pseudogap energy. Moreover, we demonstrate directly that these phenomena arise from electronic differences at the two oxygen sites within each unit cell. If the characteristics of the pseudogap seen here and by other techniques all have the same microscopic origin, this phase involves weak magnetic states at the O sites that break 90°-rotational symmetry within every CuO2 unit cell.
- 25Kasahara, S.; Shi, H.; Hashimoto, K.; Tonegawa, S.; Mizukami, Y.; Shibauchi, T.; Sugimoto, K.; Fukuda, T.; Terashima, T.; Nevidomskyy, A. H.; Matsuda, Y. Electronic nematicity above the structural and superconducting transition in BaFe2(As1-xPx)2 Nature 2012, 486, 382 DOI: 10.1038/nature1117825Electronic nematicity above the structural and superconducting transition in BaFe2(As1-xPx)2Kasahara, S.; Shi, H. J.; Hashimoto, K.; Tonegawa, S.; Mizukami, Y.; Shibauchi, T.; Sugimoto, K.; Fukuda, T.; Terashima, T.; Nevidomskyy, Andriy H.; Matsuda, Y.Nature (London, United Kingdom) (2012), 486 (7403), 382-385CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)Electronic nematicity, a unidirectional self-organized state that breaks the rotational symmetry of the underlying lattice, was obsd. in the Fe pnictide and Cu oxide high-temp. superconductors. Whether nematicity plays an equally important role in these two systems is highly controversial. In Fe pnictides, the nematicity has usually been assocd. with the tetragonal-to-orthorhombic structural transition at temp. Ts. Although recent expts. have provided hints of nematicity, they were performed either in the low-temp. orthorhombic phase or in the tetragonal phase under uniaxial strain, both of which break the 90° rotational C4 symmetry. Therefore, the question remains open whether the nematicity can exist above Ts without an external driving force. Here we report magnetic torque measurements of the isovalent-doping system BaFe2(As1-xPx)2, showing that the nematicity develops well above Ts and, moreover, persists to the non-magnetic superconducting regime, resulting in a phase diagram similar to the pseudogap phase diagram of the Cu oxides. By combining these results with synchrotron x-ray measurements, we identify two distinct temps.-one at T*, signifying a true nematic transition, and the other at Ts (<T*), which we show not to be a true phase transition, but rather what we refer to as a meta-nematic transition', in analogy to the well-known meta-magnetic transition in the theory of magnetism.
- 26Fujita, K.; Hamidian, M. H.; Edkins, S. D.; Kim, C. K.; Kohsaka, Y.; Azuma, M.; Takano, M.; Takagi, H.; Eisaki, H.; Uchida, S.-i.; Allais, A.; Lawler, M. J.; Kim, E.-A.; Sachdev, S.; Davis, J. C. S. Direct phase-sensitive identification of a d-form factor density wave in underdoped cuprates Proc. Natl. Acad. Sci. U. S. A. 2014, 111, E3026 DOI: 10.1073/pnas.1406297111There is no corresponding record for this reference.
- 27Nakaoka, H.; Yamakawa, Y.; Kontani, H. Theoretical prediction of nematic orbital-ordered state in the Ti oxypnictide superconductor BaTi2(As, Sb)2O Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 245122 DOI: 10.1103/PhysRevB.93.245122There is no corresponding record for this reference.
- 28Davies, N. R.; Johnson, R. D.; Princep, A. J.; Gannon, L. A.; Ma, J.-Z.; Qian, T.; Richard, P.; Li, H.; Shi, M.; Nowell, H. Coupled commensurate charge density wave and lattice distortion in Na2Ti2Pn2O (Pn = As, Sb) determined by X-ray diffraction and angle-resolved photoemission spectroscopy Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 94, 104515 DOI: 10.1103/PhysRevB.94.104515There is no corresponding record for this reference.
- 29Kuroki, K.; Usui, H.; Onari, S.; Arita, R.; Aoki, H. Pnictogen height as a possible switch between high-Tc nodeless and low-Tc nodal pairings in the iron-based superconductors Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 224511 DOI: 10.1103/PhysRevB.79.224511There is no corresponding record for this reference.
- 30Miyake, T.; Nakamura, K.; Arita, R.; Imada, M. Comparison of ab initio low-energy models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe: electron correlation and covalency J. Phys. Soc. Jpn. 2010, 79, 044705 DOI: 10.1143/JPSJ.79.04470530Comparison of ab initio low-energy models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe: electron correlation and covalencyMiyake, Takashi; Nakamura, Kazuma; Arita, Ryotaro; Imada, MasatoshiJournal of the Physical Society of Japan (2010), 79 (4), 044705/1-044705/20CODEN: JUPSAU; ISSN:0031-9015. (Physical Society of Japan)Effective low-energy Hamiltonians for several different families of iron-based superconductors are compared after deriving them from the downfolding scheme based on first-principles calcns. Systematic dependences of the derived model parameters on the families are elucidated, many of which are understood from the systematic variation of the covalency between Fe-3d and pnictogen-/chalcogen-p orbitals. First, LaFePO, LaFeAsO (1111), BaFe2As2 (122), LiFeAs (111), FeSe, and FeTe (11) have overall similar band structures near the Fermi level, where the total widths of 10-fold Fe-3d bands are mostly around 4.5 eV. However, the derived effective models of the 10-fold Fe-3d bands (d model) for FeSe and FeTe have substantially larger effective onsite Coulomb interactions U ∼ 4.2 and 3.4 eV, resp., after the screening by electrons on other bands and after averaging over orbitals, as compared to ∼2.5 eV for LaFeAsO. The difference is similar in the effective models contg. p orbitals of As, Se or Te (dp or dpp model), where U ranges from ∼4 eV for the 1111 family to ∼7 eV for the 11 family. The exchange interaction J has a similar tendency. The family dependence of models indicates a wide variation ranging from weak correlation regime (LaFePO) to substantially strong correlation regime (FeSe). The origin of the larger effective interaction in the 11 family is ascribed to smaller spread of the Wannier orbitals generating larger bare interaction, and to fewer screening channels by the other bands. This variation is primarily derived from the distance h between the pnictogen/chalcogen position and the Fe layer: The longer h for the 11 family generates more ionic character of the bonding between iron and anion atoms, while the shorter h for the 1111 family leads to more covalent-bonding character, the larger spread of the Wannier orbitals, and more efficient screening by the anion p orbitals. The screened interaction of the d model is strongly orbital dependent, which is also understood from the Wannier spread. The dp and dpp models show much weaker orbital dependence. The larger h also explains why the 10-fold 3d bands for the 11 family are more entangled with the smearing of the "pseudogap" structure above the Fermi level seen in the 1111 family. While the family-dependent semimetallic splitting of the bands primarily consists of dyz/dzx and dx2-y2 orbitals, the size of the pseudogap structure is controlled by the hybridization between these orbitals and dxy/d3z2-r2: A large hybridization in the 1111 family generates a large "band-insulating"-like pseudogap (hybridization gap), whereas a large h in the 11 family weakens them, resulting in a "half-filled" like bands of orbitals. This may enhance strong correlation effects in analogy with Mott physics and causes the orbital selective crossover in the three orbitals. On the other hand, the geometrical frustration t'/t, inferred from the ratio of the next-nearest transfer r' to the nearest one t of the d model is relatively larger for the 1111 family than the 11 one. The models comprehensively derived here may serve as a firm starting basis of understanding both common and diverse properties of the iron-based superconductors including magnetism and supercond.
- 31Singh, D. J. Electronic structure, disconnected Fermi surfaces and antiferromagnetism in the layered pnictide superconductor NaxBa1-xTi2Sb2O New J. Phys. 2012, 14, 123003 DOI: 10.1088/1367-2630/14/12/123003There is no corresponding record for this reference.
- 32Yan, X.-W.; Lu, Z.-Y. Layered pnictide-oxide Na2Ti2Pn2O (Pn = As, Sb): a candidate for spin density waves J. Phys.: Condens. Matter 2013, 25, 365501 DOI: 10.1088/0953-8984/25/36/36550132Layered pnictide-oxide Na2Ti2Pn2O (Pn = As, Sb). A candidate for spin density wavesYan, Xun-Wang; Lu, Zhong-YiJournal of Physics: Condensed Matter (2013), 25 (36), 365501, 9 pp.CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)From 1st-principles calcns., we have studied the electronic and magnetic structures of compd. Na2Ti2Pn2O (Pn = As or Sb), whose crystal structure is a bridge between or a combination of those of high-Tc superconducting cuprates and Fe pnictides. We find that in the ground state Na2Ti2As2O is a novel blocked checkerboard antiferromagnetic semiconductor with a small band gap of about 0.15 eV. In contrast, Na2Ti2Sb2O is a bi-collinear antiferromagnetic semimetal, with a small moment of about 0.5 μB around each Ti atom. We show that there is a strong Fermi surface nesting in Na2Ti2Pn2O, and we verify that the blocked checkerboard and bi-collinear antiferromagnetic states both are the spin d. waves induced by the Fermi surface nesting. A tetramer structural distortion is found in company with the formation of a blocked checkerboard antiferromagnetic order, in good agreement with the exptl. obsd. commensurate structural distortion but with space group symmetry retained after the anomaly happens.
- 33Suetin, D.; Ivanovskii, A. Structural, electronic properties, and chemical bonding in quaternary layered titanium pnictide-oxides Na2Ti2Pn2O and BaTi2Pn2O (Pn = As, Sb) from FLAPW-GGA calculations J. Alloys Compd. 2013, 564, 117 DOI: 10.1016/j.jallcom.2013.02.15533Structural, electronic properties, and chemical bonding in quaternary layered titanium pnictide-oxides Na2Ti2Pn2O and BaTi2Pn2O (Pn = As, Sb) from FLAPW-GGA calculationsSuetin, D. V.; Ivanovskii, A. L.Journal of Alloys and Compounds (2013), 564 (), 117-124CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)By the 1st-principles FLAPW-GGA calcns., we have investigated the main trends in structural, electronic properties, and chem. bonding for a series of quaternary Ti pnictide-oxides: Na2Ti2As2O, Na2Ti2Sb2O, BaTi2As2O, and BaTi2Sb2O, which attracted now much attention as parent phases for a novel group of layered Fe-free superconducting materials. Our results cover the optimized lattice parameters and at. positions, electronic bands, Fermi surface topol., total and partial d. of electronic states. Besides, Bader anal. and the charge d. maps are used to discuss the chem. bonding for the examd. materials. We find that the at. substitutions lead to anisotropic deformation of the crystal structure; this effect is related to strong anisotropy of interat. bonds, which are of a mixed (covalent-ionic-metallic) type - in blocks [Ti2Pn2O], whereas the bonding between blocks [Ti2Pn2O] and at. sheets of Na, Ba ions is of an ionic type. The actual effective at. charges differ from the formal ionic charges due to covalency in blocks [Ti2Pn2O]. The near-Fermi electronic bands, which are responsible for metallic-like behavior of these materials and will be involved in the formation of superconducting state, arise mainly from the Ti 3dxy, dx2-y2, and dz2 states of the blocks [Ti2Pn2O], which define also the anisotropic character of conduction happening mainly in these blocks. The differences in the topol. of the multi-sheet Fermi surfaces of these materials are discussed.
- 34Chen, D.; Zhang, T.-T.; Song, Z.-D.; Li, H.; Zhang, W.-L.; Qian, T.; Luo, J.-L.; Shi, Y.-G.; Fang, Z.; Richard, P.; Ding, H. New phase transition in Na2Ti2As2O revealed by Raman scattering Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 140501 DOI: 10.1103/PhysRevB.93.140501There is no corresponding record for this reference.
- 35
Note that we need to take special care when comparing our calculated geometry with an experimental one due to Davis et al. (28) We found that the atomic positions listed in their Table 1 are incompatible with their superstructure vectors,
,
, and
, described in their main text: (28) (1) If the description in the main text is assumed to be correct, then Na and Sb positions in the superstructure are respectively located unlikely far from their undistorted positions. (2) O is not located at (0.0, 0.0) in their Figure 6a, being inconsistent with their Table 1. Accordingly, we speculate that they again define the superstructure vectors compatible with the atomic positions in their Table 1, which differs from that in their main text. We also found y = 0.0 for As3 in their Table 1 must be a typo and correctly y = 0.25 because As3 should occupy 8j Wyckoff site and its undistorted position is y = 0.5. Assuming our speculation is correct, our optimized geometry parameters agree well with their experimental values.
There is no corresponding record for this reference. - 36Van De Walle, A.; Ceder, G. The effect of lattice vibrations on substitutional alloy thermodynamics Rev. Mod. Phys. 2002, 74, 11 DOI: 10.1103/RevModPhys.74.1136The effect of lattice vibrations on substitutional alloy thermodynamicsVan De Walle, A.; Ceder, G.Reviews of Modern Physics (2002), 74 (1), 11-45CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)A review. A long-standing limitation of first-principles calcns. of substitutional alloy phase diagrams is the difficulty in accounting for lattice vibrations. A survey of the theor. and exptl. literature seeking to quantify the effect of lattice vibrations on phase stability indicates that they can be significant. Typical vibrational entropy differences between phases are of the order of 0.1 to 0.2 kB/atom, which is comparable to the typical values of configurational entropy differences in binary alloys (at most 0.693 kB/atom). This article presents the basic formalism underlying ab initio phase diagram calcns., along with the generalization required to account for lattice vibrations. The authors review the various techniques allowing the theor. calcn. and the exptl. detn. of phonon dispersion curves and related thermodn. quantities, such as vibrational entropy or free energy. A clear picture of the origin of vibrational entropy differences between phases in an alloy system is presented that goes beyond the traditional bond counting and vol. change arguments. Vibrational entropy change can be attributed to the changes in chem. bond stiffness assocd. with the changes in bond length that take place during a phase transformation. This so-called "bond stiffness vs. bond length" interpretation both summarizes the key phenomenon driving vibrational entropy changes and provides a practical tool to model them.
- 37Whangbo, M.-H.; Koo, H.-J.; Villesuzanne, A.; Pouchard, M. Effect of Metal-Oxygen Covalent Bonding on the Competition between Jahn-Teller Distortion and Charge Disproportionation in the Perovskites of High-Spin d4 Metal Ions LaMnO3 and CaFeO3 Inorg. Chem. 2002, 41, 1920 DOI: 10.1021/ic0110427There is no corresponding record for this reference.
- 38Cammarata, A.; Rondinelli, J. M. Covalent dependence of octahedral rotations in orthorhombic perovskite oxides J. Chem. Phys. 2014, 141, 114704 DOI: 10.1063/1.489596738Covalent dependence of octahedral rotations in orthorhombic perovskite oxidesCammarata, Antonio; Rondinelli, James M.Journal of Chemical Physics (2014), 141 (11), 114704/1-114704/10CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)The compositional dependence of metal-O BO6 octahedral distortions, including bond elongations and rotations, is frequently discussed in the ABO3 perovskite literature; structural distortions alleviate internal stresses driven by under- or over-coordinated bond environments. Here the authors identify the dependence of octahedral rotations from changes in metal-O bond covalency in orthorhombic perovskites. Using d. functional theory the authors formulate a covalency metric, which captures both the real and k-space interactions between the magnitude and sense, i.e., in-phase or out-of-phase, octahedral rotations, to explore the link between the ionic-covalent Fe-O bond and the interoctahedral Fe-O-Fe bond angles in Pbnm ferrates. The authors' survey finds that the covalency of the metal-O bond is correlated with the rotation amplitude: the more covalent the Fe-O bond, the less distorted is the structure and the more important the long-range inter-octahedral (Fe-O-Fe bond angle) interactions were found. Finally, to indirectly tune the B-O bond covalency by A-cation induced BO6 rotations independent of ionic size, facilitating design of targeted bonding interactions in complex perovskites. (c) 2014 American Institute of Physics.
- 39Hughbanks, T.; Hoffmann, R. Chains of trans-edge-sharing molybdenum octahedra: metal-metal bonding in extended systems J. Am. Chem. Soc. 1983, 105, 3528 DOI: 10.1021/ja00349a02739Chains of trans-edge-sharing molybdenum octahedra: metal-metal bonding in extended systemsHughbanks, Timothy; Hoffmann, RoaldJournal of the American Chemical Society (1983), 105 (11), 3528-37CODEN: JACSAT; ISSN:0002-7863.A detailed anal. of bonding in systems with chains of condensed Mo octahedra is given. A 1-dimensional model proves to be applicable over the range of molybdates yet synthesized. The electronic coupling between chains is discussed. Distortions in newly synthesized quaternary systems are seen to result from increased electron count on the Mo chains. The band theoretic explanation of these distortions parallels the treatment of 2nd-order Jahn-Teller distortions.
- 40Dronskowski, R.; Bloechl, P. E. Crystal orbital Hamilton populations (COHP): energy-resolved visualization of chemical bonding in solids based on density-functional calculations J. Phys. Chem. 1993, 97, 8617 DOI: 10.1021/j100135a01440Crystal orbital Hamilton populations (COHP): energy-resolved visualization of chemical bonding in solids based on density-functional calculationsDronskowski, Richard; Bloechl, Peter E.Journal of Physical Chemistry (1993), 97 (33), 8617-24CODEN: JPCHAX; ISSN:0022-3654.After giving a concise overview of the current knowledge in the field of quantum mech. bonding indicators for mols. and solids, the authors show how to obtain energy-resolved visualization of chem. bonding in solids by d.-functional electronic structure calcns. From a band structure energy partitioning scheme, i.e., rewriting the band structure energy as a sum of orbital pair contributions, the authors derive what is to be defined as crystal orbital Hamilton populations (COHP). In particular, a COHP(ε) diagram indicates bonding, nonbonding, and antibonding energy regions within a specified energy range while an energy integral of a COHP gives access to the contribution of an atom or a chem. bond to the distribution of 1-particle energies. A further decompn. into specific AOs or symmetry-adapted linear combinations of AOs (hybrids) can easily be performed by using a projector technique involving unitary transformations. Because of its structural simplicity and the availability of reliable thermodn. data, the authors study the bonding within cryst. silicon (diamond phase) 1st. As a basis set, both bcc. screened and diamond screened at.-centered tight-binding linear muffin-tin orbitals (TB-LMTOs) are used throughout. The shape of COHP vs. energy diagrams and the significance of COHP subcontributions (s-s, sp3-sp3) are analyzed. Specifically, the difference between the COHPs energy integral (1-particle bond energy) and the exptl. bond energy is critically examd. While abs. values for the 1-particle bond energy show a high basis set dependence due to changing on-site (crystal field) COHP terms, the shape of off-site (bonding) COHP functions, elucidating the local bonding principle within an extended structure, remains nearly unaffected.
- 41Grechnev, A.; Ahuja, R.; Eriksson, O. Balanced crystal orbital overlap population—a tool for analysing chemical bonds in solids J. Phys.: Condens. Matter 2003, 15, 7751 DOI: 10.1088/0953-8984/15/45/01441Balanced crystal orbital overlap population-a tool for analysing chemical bonds in solidsGrechnev, Alexei; Ahuja, Rajeev; Eriksson, OlleJournal of Physics: Condensed Matter (2003), 15 (45), 7751-7761CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)A new tool for analyzing theor. the chem. bonding in solids is proposed. A balanced crystal orbital overlap population (BCOOP) is an energy resolved quantity which is pos. for bonding states and neg. for antibonding states, hence enabling a distinction between bonding and antibonding contributions to the chem. bond. Unlike the conventional crystal orbital overlap population (COOP), BCOOP handles correctly the situation of crystal orbitals being nearly linear dependent, which is often the case in the solid state. Also, BCOOP is much less basis set dependent than COOP. A BCOOP implementation within the full-potential linear muffin tin orbital method is presented and illustrated for Si, TiC and Ru. Thus, BCOOP is compared to the COOP and crystal orbital Hamilton population (COHP) for systems with chem. bonds ranging from metallic to covalent character.
- 42
The angle of O–Ti–Pn becomes 87° even at the most stable point for Pn = Sb. The corresponding displacement is 0.125 Å (Figure 9a). In this case, the restoring force between Ti and the nearest O contributing to the direction of the displacement is negligible because cos(87°) is only 0.05.
There is no corresponding record for this reference. - 43Zhang, G.; Glasbrenner, J. K.; Flint, R.; Mazin, I. I.; Fernandes, R. M. Double-stage nematic bond ordering above double stripe magnetism: Application to BaTi2Sb2O Phys. Rev. B: Condens. Matter Mater. Phys. 2017, 95, 174402 DOI: 10.1103/PhysRevB.95.174402There is no corresponding record for this reference.
- 44Fan, G.; Zhang, X.; Shi, Y.; Luo, J. Charge density wave transition in Na2Ti2Sb2O probed by 23Na NMR Sci. China: Phys., Mech. Astron. 2013, 56, 2399 DOI: 10.1007/s11433-013-5347-344Charge density wave transition in Na2Ti2Sb2O probed by 23Na NMRFan, Guo Zhi; Zhang, Xu; Shi, You Guo; Luo, Jian LinScience China: Physics, Mechanics & Astronomy (2013), 56 (12), 2399-2403CODEN: SCPMCL; ISSN:1674-7348. (Springer)Herein we investigated the electronic properties of layered transition-metal oxides Na2Ti2Sb2O by 23Na NMR (NMR) measurement. The resistivity, susceptibility and sp. heat measurements show a phase transition at approx. 114 K (TA). No splitting or broadening in the central line of 23Na NMR spectra is obsd. below and above the transition temp. indicating no internal field being detected. The spin-lattice relaxation rate divided by T (1/T1T) shows a sharp drop at about 110 K which suggests a gap opening behavior. Below the phase transition temp. zone, 1/T1T shows Fermi liq. behavior but with much smaller value indicating the loss of large part of electronic d. of states (DOS) because of the gap. No signature of the enhancement of spin fluctuations or magnetic order is found with the decreasing temp. These results suggest a commensurate charge-d.-wave (CDW) phase transition occurring.
- 45Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple Phys. Rev. Lett. 1996, 77, 3865 DOI: 10.1103/PhysRevLett.77.386545Generalized gradient approximation made simplePerdew, John P.; Burke, Kieron; Ernzerhof, MatthiasPhysical Review Letters (1996), 77 (18), 3865-3868CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Generalized gradient approxns. (GGA's) for the exchange-correlation energy improve upon the local spin d. (LSD) description of atoms, mols., and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental consts. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential.
- 46Giannozzi, P. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials J. Phys.: Condens. Matter 2009, 21, 395502 DOI: 10.1088/0953-8984/21/39/39550246QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materialsGiannozzi Paolo; Baroni Stefano; Bonini Nicola; Calandra Matteo; Car Roberto; Cavazzoni Carlo; Ceresoli Davide; Chiarotti Guido L; Cococcioni Matteo; Dabo Ismaila; Dal Corso Andrea; de Gironcoli Stefano; Fabris Stefano; Fratesi Guido; Gebauer Ralph; Gerstmann Uwe; Gougoussis Christos; Kokalj Anton; Lazzeri Michele; Martin-Samos Layla; Marzari Nicola; Mauri Francesco; Mazzarello Riccardo; Paolini Stefano; Pasquarello Alfredo; Paulatto Lorenzo; Sbraccia Carlo; Scandolo Sandro; Sclauzero Gabriele; Seitsonen Ari P; Smogunov Alexander; Umari Paolo; Wentzcovitch Renata MJournal of physics. Condensed matter : an Institute of Physics journal (2009), 21 (39), 395502 ISSN:.QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.
- 47Blöchl, P. E. Projector augmented-wave method Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953 DOI: 10.1103/PhysRevB.50.1795347Projector augmented-wave methodBlochlPhysical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.There is no expanded citation for this reference.
- 48Jollet, F.; Torrent, M.; Holzwarth, N. Generation of Projector Augmented-Wave atomic data: A 71 element validated table in the XML format Comput. Phys. Commun. 2014, 185, 1246 DOI: 10.1016/j.cpc.2013.12.02348Generation of Projector Augmented-Wave atomic data: A 71 element validated table in the XML formatJollet, Francois; Torrent, Marc; Holzwarth, NatalieComputer Physics Communications (2014), 185 (4), 1246-1254CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)In the Projector Augmented Wave (PAW) method developed by Bloechl (1994), a PAW data file is needed for each element, taking the role of the pseudopotential file used with the norm-conserving or ultrasoft formalisms. In this paper, we review methods for generating PAW data files and for evaluating their accuracy, transferability, and numerical efficiency in simulations of bulk solids. We have developed a new set of PAW at. data files for most of the stable elements in the periodic table. These files are provided in a std. XML format for use in any PAW electronic structure code. The new dataset performs well as measured by the "Δ" evaluation criterion introduced by Lejaeghere et al. (2014), and also performs well in a modified evaluation scheme proposed in the present paper.
- 49Kucukbenli, E.; Monni, M.; Adetunji, B.; Ge, X.; Adebayo, G.; Marzari, N.; de Gironcoli, S.; Corso, A. D. Projector augmented-wave and all-electron calculations across the periodic table: a comparison of structural and energetic properties. 2014, arXiv:cond-mat.mtrl-sci/1404.3015. arXiv.org e-Print archive. https://arxiv.org/abs/1404.3015 (accessed July 6, 2017).There is no corresponding record for this reference.
- 50Baroni, S.; de Gironcoli, S.; Dal Corso, A.; Giannozzi, P. Phonons and related crystal properties from density-functional perturbation theory Rev. Mod. Phys. 2001, 73, 515 DOI: 10.1103/RevModPhys.73.51550Phonons and related crystal properties from density-functional perturbation theoryBaroni, Stefano; De Gironcoli, Stefano; Dal Corso, Andrea; Giannozzi, PaoloReviews of Modern Physics (2001), 73 (2), 515-562CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)This article reviews with many refs. the current status of lattice-dynamical calcns. in crystals, using d.-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calcn. of the response to macroscopic elec. fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodol. is demonstrated with a no. of applications existing in the literature.
- 51Momma, K.; Izumi, F. VESTA3 for three-dimensional visualization of crystal, volumetric and morphology data J. Appl. Crystallogr. 2011, 44, 1272 DOI: 10.1107/S002188981103897051VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology dataMomma, Koichi; Izumi, FujioJournal of Applied Crystallography (2011), 44 (6), 1272-1276CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)VESTA is a 3D visualization system for crystallog. studies and electronic state calcns. It was upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphpol. of crysals; superimposing multiple structural models, volumetric data and crystal faces; calcn. of electron and nuclear densities from structure parameters; calcn. of Patterson functions from the structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels, detn. of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex mols. and cage-like structures; undo and redo is graphical user interface operations; and significant performance improvements in rendering isosurfaces and calcg. slices.
- 52Kokalj, A. XCrySDen a new program for displaying crystalline structures and electron densities J. Mol. Graphics Modell. 1999, 17, 176 DOI: 10.1016/S1093-3263(99)00028-552XCrySDen--a new program for displaying crystalline structures and electron densitiesKokalj AJournal of molecular graphics & modelling (1999), 17 (3-4), 176-9, 215-6 ISSN:1093-3263.XCrySDen is a molecular and crystalline-structure visualization program, but its main function is as a property analyzer program. It can run on most UNIX platforms, without any special hardware or software requirements. Special efforts were made to allow for appropriate display of 3D isosurfaces and 2D contours, which can be superimposed on crystalline structure and interactively rotated and manipulated. XCrySDen is also a graphical user interface for the CRYSTAL95/98 (Saunders, V. R., et al. CRYSTAL98--User's Manual. University of Torino, Turin, Italy, 1999) ab initio program and a visualization system for the WIEN97 (Blaha, P., et al. Comput. Phys. Commun. 1990, 59, 399) ab initio program. In this article the program functions are presented with a short description of the algorithms.
- 53Marzari, N.; Vanderbilt, D.; De Vita, A.; Payne, M. C. Thermal Contraction and Disordering of the Al(110) Surface Phys. Rev. Lett. 1999, 82, 3296 DOI: 10.1103/PhysRevLett.82.329653Thermal Contraction and Disordering of the Al(110) SurfaceMarzari, Nicola; Vanderbilt, David; De Vita, Alessandro; Payne, M. C.Physical Review Letters (1999), 82 (16), 3296-3299CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Al(110) has been studied for temps. up to 900 K via ensemble d.-functional mol. dynamics. The strong anharmonicity displayed by this surface results in a neg. coeff. of thermal expansion, where the first interlayer distance decreases with increasing temp. Very shallow channels of oscillation for the second-layer atoms in the direction perpendicular to the surface support this anomalous contraction, and provide a novel mechanism for the formation of adatom-vacancy pairs, preliminary to the disordering and premelting transition. Such characteristic behavior originates in the free-electron-gas bonding at a loosely packed surface.
- 54Ozawa, T. C.; Pantoja, R.; Axtell, E. A.; Kauzlarich, S. M.; Greedan, J. E.; Bieringer, M.; Richardson, J. W. Powder Neutron Diffraction Studies of Na2Ti2Sb2O and Its Structure Property Relationships J. Solid State Chem. 2000, 153, 275– 281 DOI: 10.1006/jssc.2000.875854Powder neutron diffraction studies of Na2Ti2Sb2O and its structure-property relationshipsOzawa, Tadashi C.; Pantoja, Rigo; Axtell, Enos A., III; Kauzlarich, Susan M.; Greedan, John E.; Bieringer, Mario; Richardson, James W., Jr.Journal of Solid State Chemistry (2000), 153 (2), 275-281CODEN: JSSCBI; ISSN:0022-4596. (Academic Press)The structure of Na2Ti2Sb2O was studied by temp.-dependent powder neutron diffraction. Na2Ti2Sb2O crystallizes in I4/mmm symmetry. The structure of this phase can be viewed as an anti-K2NiF4 type where Ti3+ ion is located between two O atoms forming a square-planar lattice. Powder neutron diffraction studies of Na2Ti2Sb2O indicate that this compd. has a structural distortion in the [Ti2Sb2O]2- layer at T ≈ 120 K. This transition corresponds well to the previously reported anomalous transition temp. of the magnetic susceptibility and electronic resistivity. Several models to explain the data are presented and discussed. (c) 2000 Academic Press.