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C: Energy Conversion and Storage

Synthesis, Crystal Structure, and Hydrogen Storage Properties of an AB3-Based Alloy Synthesized by Disproportionation Reactions of AB2-Based Alloys
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  • Toyoto Sato*
    Toyoto Sato
    Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-0527-1235
  • Hiroyuki Saitoh
    Hiroyuki Saitoh
    National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan
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  • Reina Utsumi
    Reina Utsumi
    National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan
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  • Jyunya Ito
    Jyunya Ito
    Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
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  • Kazuki Obana
    Kazuki Obana
    Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
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  • Yuki Nakahira
    Yuki Nakahira
    National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan
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    Orcidhttps://orcid.org/0000-0003-0241-0786
  • Denis Sheptyakov
    Denis Sheptyakov
    Laboratory for Neutron Scattering and Imaging, PSI Center for Neutron and Muon Sciences, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
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  • Takashi Honda
    Takashi Honda
    Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
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    Orcidhttps://orcid.org/0000-0003-4121-8957
  • Hajime Sagayama
    Hajime Sagayama
    Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
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  • Shigeyuki Takagi
    Shigeyuki Takagi
    National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan
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  • Tatsuoki Kono
    Tatsuoki Kono
    Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
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  • Heena Yang
    Heena Yang
    Water Energy Research Center, Korea Water Resources Corporation, 125 Yuseong-daero 1689beon-gil, Yuseong-gu, Daejeon 34045, Republic of Korea
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  • Wen Luo
    Wen Luo
    School of Environmental and Chemical Engineering, Shanghai University, Shangda Road 99, 200444 Shanghai, China
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    Orcidhttps://orcid.org/0000-0003-4250-6168
  • Loris Lombardo
    Loris Lombardo
    Laboratory of Materials for Renewable Energy (LMER), Institute of Chemical Sciences and Engineering (ISIC), Basic Science Faculty (SB), École Polytechnique Fédérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Rue de l’Industrie 17, CH-1951 Sion, Switzerland
    Empa Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
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    Orcidhttps://orcid.org/0000-0003-2968-6686
  • Andreas Züttel
    Andreas Züttel
    Laboratory of Materials for Renewable Energy (LMER), Institute of Chemical Sciences and Engineering (ISIC), Basic Science Faculty (SB), École Polytechnique Fédérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Rue de l’Industrie 17, CH-1951 Sion, Switzerland
    Empa Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
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  • Shin-ichi Orimo
    Shin-ichi Orimo
    Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
    Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
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The Journal of Physical Chemistry C

Cite this: J. Phys. Chem. C 2025, 129, 6, 2865–2873
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https://doi.org/10.1021/acs.jpcc.4c06759
Published February 2, 2025

Copyright © 2025 The Authors. Published by American Chemical Society. This publication is licensed under

CC-BY 4.0 .

Abstract

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Hydrogen storage materials store hydrogen in their atomic states, enabling more compact and safer storage methods compared to those for gaseous and liquid hydrogen. Although various types of hydrogen storage materials have been reported, new materials with higher hydrogen storage capacities and enhanced durability are required. Herein, we report the synthesis, crystal structure, and hydrogen storage properties of an AB3-based alloy, Y0.68Mg0.32Co3.00, which exhibited reversible hydrogen absorption and desorption with a hydrogen storage capacity of 1.68 mass % and minimal degradation over 100 cycles at 303 K. The hydrogen storage capacity of Y0.68Mg0.32Co3.00 exceeds that of LaNi5, a reported hydrogen storage material with 1.38 mass %. It further increased to 2.88 mass % at room temperature under 10 GPa. This finding suggests that Y0.68Mg0.32Co3.00 has the potential for even greater hydrogen storage capacity. This could lead to more compact and lightweight storage solutions for hydrogen energy devices.

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Introduction

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Hydrogen storage is essential for the development of hydrogen-based societies. Currently, gaseous hydrogen, liquid hydrogen, and material-based methods are promising candidates for hydrogen storage. Although various material-based methods have been reported, storing hydrogen atoms in the interstitial sites of intermetallic compounds, commonly referred to as hydrogen storage materials or alloys, is considered a more compact and safer approach compared to other candidates. In the design of hydrogen storage materials, elements from Groups 1–5 of the periodic table, designated as component A, are typically selected and alloyed with elements from Groups 6–12, designated as component B. (1−3) For instance, AB2, AB3, and AB5 are typical hydrogen storage materials. (3) Alloys AB2 are called Laves phase alloys. As hydrogen atoms are stored in the interstitial sites of hydrogen storage materials, understanding their atomic arrangements has been crucial for elucidating the mechanisms of hydrogen absorption and desorption reactions. Focusing on the typical crystal structures of AB2, AB3, and AB5 (Figure 1 (4,5)), the stacking of two different polyhedra, a Laves polyhedron and a capped hexagonal prism, has been investigated. The crystal structures of AB2 and AB5 are composed of a Laves polyhedron and capped hexagonal prism, respectively. Therefore, in this study, we refer to the Laves polyhedron and capped hexagonal prism as AB2 and AB5 units, respectively. The crystal structure of AB3 comprises AB2 and AB5 units, indicating that AB3 has the characteristic features of AB2 and AB5 as hydrogen storage materials. (6−11)

Figure 1

Figure 1. Crystal structures of AB2, AB3, and AB5. In the crystal structure, A and B atoms are represented as gray and green spheres, respectively. Capped hexagonal prism and Laves polyhedra are represented as orange and green polyhedra, respectively.

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In our previous studies focusing on AB2-based alloys, we reported reversible hydrogen storage materials based on YMgNi4 synthesized from the binary alloys, YNi2 and MgNi2. (12,13) YMgNi4 exhibits a similar atomic arrangement to AB2 with a cubic crystal structure (C15). (14) The key difference lies in the atomic arrangement of Y and Mg in YMgNi4. In this structure, Y and Mg atoms are predominantly ordered, whereas if YMgNi4 had the cubic crystal structure (C15) of AB2, the Y and Mg atoms would be completely disordered. (13) This finding suggests that the hydrogen storage properties (equilibrium hydrogen pressures and hydrogen storage capacities) can be controlled by the site occupancies of the Y and Mg atomic positions. Materials related to YMgNi4 as hydrogen storage materials have been previously reported. (14−30) In addition, substituting a part of Ni with Co could potentially lead to a lower equilibrium hydrogen pressure and higher hydrogen storage capacities. Neutron diffraction and inelastic neutron scattering experiments on YMgNi4-based alloys with and without Co suggested that Co in the YMgNi4-based alloy led to more disordered hydrogen atoms compared with YMgNi4 without Co. (30) The disordering of hydrogen atoms could be associated with a lower equilibrium hydrogen pressure, leading to higher hydrogen storage capacities. Co substitution effects have also been reported by Shtender et al. (24−26,28) In their studies, YMgCo4 and related intermetallic compounds exhibited the highest hydrogen storage capacities in the YMg(Ni, Co)4 system. (24) Hence, Co is hypothesized to improve the hydrogen storage properties of AB2 and related materials.
Using AB2 alloys with Co, YCo2, and MgCo2, as starting materials in our study, AB3-based alloys were obtained at higher temperatures than those used in the syntheses of YMgNi4-based alloys. In this study, we refer to the AB3-based alloys as (Y, Mg)Co3. Evaporation of Mg at higher temperatures and similarities in the crystal structures, as mentioned earlier, could lead to disproportionation reactions. Notably, the AB3-based alloys exhibited narrower hysteresis of hydrogen absorption and desorption pressures and superior cycling performance and durability to the YMgNi4-based alloys. Therefore, we report the synthesis, crystal structures before and after the hydrogen absorption reactions, and hydrogen storage properties. Furthermore, we investigated the hydrogen absorption reactions above 1 GPa, where the chemical potential of hydrogen increases substantially, and reactions between hydrogen and the materials occur. (31,32) We used a high-pressure apparatus to understand the potential hydrogen storage capacity of (Y, Mg)Co3.

Methods

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Syntheses

YCo2 and MgCo2 were used as starting materials for (Y, Mg)Co3. YCo2 was synthesized from Y chips (Sigma-Aldrich, 99.9) and Co shots (Rare Metallic Co., Ltd., 99.999%) in an arc-melting furnace (Nissin Gigen Corporation, NEV-AD03) at a molar ratio of 1:2. MgCo2 was synthesized from a mixture of Mg (Rare Metallic Co., Ltd., 99.9%) and Co powders (Rare Metallic Co., Ltd., 99.9%) in an induction melting furnace (Sekisui, MU-1700) at a molar ratio of 1.1:2. X-ray diffraction patterns of YCo2 and MgCo2 are shown in Figure S1 in the Supporting Information. Mixtures of YCo2 and MgCo2 at a molar ratio of 2–x and x (x = 0.8 and 1.0) were pressed into pellets of diameter 6 mm and heated at 1173 K for 24 h in an Ar atmosphere. In this study, we refer to the synthesized samples as (Y, Mg)Co3. YCo3 was synthesized from Y chips (Sigma-Aldrich, 99.9) and Co shots (Rare Metallic Co., Ltd., 99.999%) using an arc-melting furnace (Nissin Gigen Corporation, NEV-AD03) at a molar ratio of 1:3.

X-ray Diffraction

All samples were characterized by a conventional X-ray diffractometer (PANalytical X’PERT) using Cu Kα radiation (λ = 1.5406 Å for Kα1 and 1.5444 Å for Kα2).
The crystal structures of (Y, Mg)Co3 synthesized from (2–x)YCo2 and xMgCo2 (x = 0.8 and 1.0) were investigated using synchrotron radiation X-ray diffraction performed on BL-8A at the Photon Factory, High Energy Accelerator Research Organization (KEK), Japan. For the synchrotron radiation X-ray diffraction, (Y, Mg)Co3 are placed in a Lindemann glass capillary with an outer diameter of 0.3 mm and a thickness of 0.01 mm.

Neutron Diffraction

The crystal structures of (Y, Mg)Co3 synthesized from 1.2YCo2 and 0.8MgCo2 were investigated by neutron diffraction under vacuum and D2 and H2 pressures of 5 MPa using a high-resolution powder diffractometer for thermal neutrons (HRPT) (33) at the Swiss Spallation Neutron Source (SINQ), Paul Scherrer Institute (PSI), Switzerland. For neutron diffraction, approximately 4 g of (Y, Mg)Co3 powder was placed in a steel container with an outer diameter of 10 mm. Neutron diffraction data were collected using a neutron wavelength of 1.494 Å in the high-intensity mode of the instrument. A custom gas handling system was used to create the dynamic pressures of 5 MPa of H2 and D2 gases over the powder intermetallic sample.

Crystal Structure Investigations

The indexing program TREOR97, (34) least-squares refinement of the unit cell parameter program PIRUM, (35) and the Rietveld refinement program GSAS with the graphical interface EXPGUI (version 1.80) (36) were used to investigate the crystal structure using synchrotron radiation X-ray diffraction and neutron diffraction data. In the Rietveld refinement, the pseudo-Voigt peak shape function with the Finger–Cox–Jephcoat asymmetry correction was used for the synchrotron radiation X-ray diffraction data, and the standard Gaussian function modified for peak asymmetry was used for neutron diffraction data. The background was modeled using the Chebyshev polynomial function in the GSAS. Isotropic temperature–displacement parameters were used for all elements.

Hydrogen Storage Properties

The hydrogen storage properties of samples were investigated using a pressure–composition isotherm apparatus (PCT apparatus) (Suzuki Shokan Co. Ltd., PCT-3SPWIN) at 303 and 323 K up to 9 MPa of H2 gas pressure. Before the PCT measurements, the sample was heated at 473 K under vacuum for 3 h.
During the cycling between the hydrogen absorption and desorption reactions, the hydrogen absorption reactions were performed at a hydrogen gas pressure of 5 MPa at 303 K for 2 h. The hydrogen desorption reactions were performed under vacuum at 303 K for 2 h. After 2 and 99 cycles, the hydrogen storage properties were investigated using a PCT apparatus.

High Pressure Experiments above 1 GPa

Hydrogen absorption reactions of (Y, Mg)Co3 synthesized from 1.2YCo2 + 0.8MgCo2 at room temperature (above 1 GPa) were observed using a multianvil apparatus combined with synchrotron radiation X-ray diffraction at the BL14B1, SPring-8 in Japan. Before the high-pressure experiment, (Y, Mg)Co3 was heated to 473 K under vacuum for 3 h. (Y, Mg)Co3 was placed in a BN capsule enclosed with a hydrogen source, BH3NH3 (Sigma-Aldrich, 97%), in an NaCl capsule. The details of the sample cell assembling, (32) and hydrogen release reactions of BH3NH3 under high pressure are described in previous studies. (37,38) The energy-dispersive X-ray diffraction method was utilized for X-ray diffraction data collection during the high-pressure experiments. The obtained data were analyzed using PDindexer. (39)

Handling of Samples

All samples, which were starting materials for YCo2, MgCo2, as-synthesized (Y, Mg)Co3, and hydrided (Y, Mg)Co3, were handled in Ar-gas filled glove boxes with dew points of <183 K and <1 ppm of O2 to prevent (hydro-)oxidation.

Results and Discussion

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Syntheses

Figure 2 shows X-ray diffraction patterns of the (Y, Mg)Co3 synthesized from (2–x)YCo2 + xMgCo2 (x = 0.8 and 1.0) and YCo3. Most of the Bragg peaks in all samples were indexed by trigonal unit cells. The unit cell parameters are listed in Table 1. Although the X-ray diffraction patterns of (Y, Mg)Co3 are similar to those of YCo3, the Bragg peak positions and unit cell parameters of (Y, Mg)Co3 and YCo3 are slightly different. The chemical composition of the product synthesized from (2–x)YCo2 + xMgCo2 (x = 0.8 and 1.0) was determined by Rietveld refinement using synchrotron radiation X-ray diffraction (see the next section). This finding indicates that a disproportionation reaction between YCo2 and MgCo2 occurred during the heat treatment of the mixture of (2–x)YCo2 + xMgCo2. The reaction could have originated from the evaporation of Mg during heat treatment, and it yields Y2O3. The similarities in the crystal structures of AB2 and AB3 may also be related. Despite the disproportionation reactions, the unit cell parameters depend on the amount of MgCo2. Notably, the amount of Mg could be controlled by varying the ratios of starting material, as reported in our previous studies. (12,30) In the following sections, we will discuss the effect of Mg on the crystal structures and hydrogen storage properties.

Figure 2

Figure 2. X-ray diffraction patterns of (Y, Mg)Co3 synthesized from (2–x)YCo2 + xMgCo2 (x = 0.8 and 1.0), and YCo3. In the figure, allow indicates Y2O3. Si was added as an internal standard.

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Table 1. Trigonal Unit Cell Parameters of (Y, Mg)Co3 Synthesized from (2–x)YCo2 + xMgCo2 (x = 0.8 and 1.0), and YCo3
 a (Å)c (Å)V (Å3)
1.2YCo2 + 0.8MgCo24.9990(08)24.197(17)523.67(54)
1.0YCo2 + 1.0MgCo24.9823(09)24.032(14)516.63(49)
YCo35.0141(12)24.341(25)529.97(80)

Crystal Structures

Synchrotron Radiation X-ray Diffraction

The crystal structures before and after hydrogen absorption reactions were investigated using conventional and synchrotron radiation X-ray and neutron diffraction. First, we discuss the crystal structures, including the chemical composition, before the hydrogen absorption reactions, which were determined using synchrotron radiation X-ray diffraction. The Rietveld refinement fits of (Y, Mg)Co3 using synchrotron radiation X-ray diffraction are shown in Figures S2 and S3 in the Supporting Information. Using the same atomic arrangements with YCo3 as an initial structure model (40) for Rietveld refinements, in which Mg atoms are placed at two crystallographically different Y atomic positions, the experimentally observed X-ray diffraction patterns up to a higher Q range are reasonably reproduced. The crystallographic parameters of (Y, Mg)Co3 are listed in Tables S1 and S2 in the Supporting Information. The chemical compositions of (Y, Mg)Co3 synthesized from (2–x)YCo2 + xMgCo2 (x = 0.8 and 1.0) were Y0.68Mg0.32Co3.00 (x = 0.8) and Y0.58Mg0.42Co3.00 (x = 1.0). The crystal structure of Y0.68Mg0.32Co3.00 is only shown in Figure 3 because the differences between Y0.68Mg0.32Co3.00 and Y0.58Mg0.42Co3.00 are the unit cell parameters and occupancies at Y1/Mg1 and Y2/Mg2. The crystal structure was composed of stacked AB5 units (capped hexagonal prisms) and AB2 units (Laves polyhedrons). The AB5 unit is formed by Y1/Mg1 atoms surrounded by 18 Co atoms, and the AB2 unit is formed by Y2/Mg2 atoms surrounded by 12 Co atoms. By increasing the amount of Mg in (Y, Mg)Co3, the occupancy of Mg2 at 6c increased. Excess Mg was located on the AB2 unit side because the occupancies of Mg1 were maintained even with an increase in Mg. This finding is related to the hydrogen storage properties, which are discussed in the following section.

Figure 3

Figure 3. Crystal structures of (a) Y0.68Mg0.32Co3.00, and (b) Y0.68Mg0.32Co3.00D3.76. Y, Mg, Co, and D atoms are represented as gray, orange, green, and blue spheres, respectively. Y1/Mg1 surrounded by 18 Co atoms, and Y2/Mg2 surrounded by 12 Co atoms, are represented by orange and green polyhedra, respectively.

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Next, we discuss the crystal structure after the hydrogen (deuterium) absorption reaction, investigated by neutron diffraction under a D2 pressure of 5 MPa at 323 K. The hydrogen storage capacities of Y0.68Mg0.32Co3.00 were higher than those of Y0.58Mg0.42Co3.00 (see the next section); hence, the hydrogen (deuterium) atomic positions were investigated using Y0.68Mg0.32Co3.00. The Rietveld refinement fits of the Y0.68Mg0.32Co3.00 deuteride under a D2 pressure of 5 MPa at 323 K are shown in Figure S4 in the Supporting Information. Its chemical composition was found to be Y0.68Mg0.32Co3.00D3.76(11), with a gravimetric hydrogen density of 1.52 mass %. This value was close to the gravimetric hydrogen density observed by the PCT measurements at 323 K (details are available in the next section). Although the Bragg peaks of the stainless-steel sample container were removed because of their strong intensities, the experimentally observed neutron diffraction was reasonably reproduced. The crystallographic parameters are listed in Table S3 in the Supporting Information. We observed the neutron diffraction pattern of Y0.68Mg0.32Co3.00 under an H2 pressure of 5 MPa at 323 K to confirm the D atomic positions. The experimentally observed neutron diffraction pattern under H2 pressure was also reasonably reproduced using the same atomic positions as those of Y0.68Mg0.32Co3.00D3.76, in which the D atoms were replaced by H atoms. The Rietveld refinement fit is shown in Figure S5.
Based on the Rietveld refinement fits done on neutron diffraction data, we discuss the D atomic positions and the relationship between the hydrogen absorption reactions and crystal structure. In Y0.68Mg0.32Co3.00D3.76, the D atoms are located at five crystallographically different atomic sites in which D atoms are referred to as D1, D2, D3, D4, and D5 (Figure 3). Selected interatomic distances are listed in Table 2. They have reasonable interatomic distances compared to our previous work on Y–Mg–Ni–Co. (30) D1 was located inside the tetrahedra coordinated by four Co atoms (1 × Co1 and 3 × Co3). D2 was located inside the tetrahedra coordinated by four Co atoms (1 × Co2 and 3 × Co3). D3 was located inside an octahedron coordinated by four Co atoms (2 × Co2 and 2 × Co3) and two Y1/Mg1 atoms. D4 was located inside a tetrahedron coordinated by two Co atoms (2 × Co3), Y1/Mg1 and Y2/Mg2. D5 was located inside a triangular dipyramid (3 × 2/Mg2, 1 × Co1, and 1 × Co3). Focusing on the AB2 and AB5 units, the local atomic arrangements around hydrogen in Y0.68Mg0.32Co3.00D3.76 are shown in Figure 3. The D atomic positions as viewed from the AB5 and AB2 units are shown in Figure 3. The D atomic positions are primarily classified into inside the AB5 and AB2 units (intra-AB5 and intra-AB2 units) and between the AB5 and AB2 units (interunits). The D3 and D4 atoms are inside the AB5 unit, the D5 atoms are inside the AB2 unit, and D1 and D2 locate interunits. According to the D atomic positions in YCo3, (40) the D atoms in YCo3 are locate intraunits. Note that the Mg in the Y atoms may induce the placement of hydrogen atoms in interunits positions. In addition, the AB5 unit (55.9%) with less Mg contained more D atoms than the AB2 unit (32.4%). Considering the occupancies of Mg2 on Y0.68Mg0.32Co3.00 and Y0.58Mg0.42Co3.00, Y0.68Mg0.32Co3.00 possessed less Mg atoms in the Y2/Mg2 site and higher hydrogen storage capacities than Y0.58Mg0.42Co3.00 (see the next section). Consequently, the hydrogen storage capacities were related to the AB2 units rather than to the AB5 units (as discussed in the next section). Therefore, the hydrogen storage capacity could increase if more hydrogen atoms were located inside the AB2 unit. Such consideration of the units can provide insights into the dependence of hydrogen storage capacities on Mg. In the next section, we discuss the relationship between the crystal structure (atomic arrangement) and hydrogen storage properties.
Table 2. Selected Interatomic Distances between D and Metal Atomsa
D atom–metal atominteratomic distances (Å)
D1-Co11.644(4)
D1-Co3 (×3)1.634(5)
D2-Co21.77(6)
D2-Co3 (×3)1.598(18)
D3-Y1/Mg1 (×2)2.63685(32)
D3-Co2 (×2)1.538(5)
D3-Co3 (×2)2.055(10)
D4-Y1/Mg12.248(6)
D4-Y2/Mg22.275(10)
D4-Co3 (×2)1.639(4)
D5-Y2/Mg2 (×2)2.6379(5)
D5-Y2/Mg21.909(4)
D5-Co11.671(5)
D5-Co31.652(6)
a

The too short D–D interatomic distances, which are D1–D5 (1.899(6) Å), D2–D4 (1.724(10) Å), and D5–D5 (1.946(11) Å), can perhaps be explained by a by-far non-perfect fits because of the too weak intensities at higher Q range in the neutron diffraction pattern.

Hydrogen Storage Properties

Figure 4 shows the PCT curves of Y0.68Mg0.32Co3.00 and Y0.58Mg0.42Co3.00 at 323 K. Both samples exhibited reversible hydrogen absorption and desorption reactions. The maximum hydrogen storage capacities at 323 K reached 1.56 mass % (of Y0.68Mg0.32Co3.00) and 1.21 mass % (Y0.58Mg0.42Co3.00), which decreased with increasing amounts of Mg. In addition, the equilibrium pressure increased with increasing amounts of Mg. The trends of hydrogen storage capacities and equilibrium hydrogen pressures were the same as those of YMgNi4-based alloys. (12,24,30) Focusing on the crystal structures of Y0.68Mg0.32Co3.00 and Y0.58Mg0.42Co3.00, the occupancies of Mg2, which were located inside the AB2 unit, increased with increasing amounts of Mg2, although those of Mg1, which were located inside the AB5 unit, were almost the same. This finding indicates that the hydrogen storage properties of (Y, Mg)Co3 depend on hydrogen atoms in the AB2 units. Therefore, the hydrogen storage properties could exhibit the same trend as the YMgNi4-based alloys and be controlled by the spaces and affinities to hydrogen on the AB2 unit sides in (Y, Mg)Co3.

Figure 4

Figure 4. Pressure–composition isotherm (PCT) curves of (black) Y0.68Mg0.32Co3.00 and (gray) Y0.58Mg0.42Co3.00 at 323 K. Closed and open circles indicate hydrogen absorption and desorption, respectively. The PCT curves in the figure are obtained in the third run.

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Next, we discuss the cycling of the hydrogen absorption and desorption reactions on Y0.68Mg0.32Co3.00 at 323 K. Figure 5 shows the PCT curves on the third and 100th cycles and the X-ray patterns before and after cycling. The PCT measurement at 303 K demonstrated that Y0.68Mg0.32Co3.00 stored 1.68 mass % hydrogen, which was higher than that of LaNi5 (1.38 mass %), a typical hydrogen storage material. In addition, it exhibited minimal degradation for up to 100 cycles and maintained its crystallinity before and after cycling. This finding could be related to the negligible hysteresis of Y0.68Mg0.32Co3.00. In contrast, the hysteresis mechanisms of the hydrogen absorption and desorption pressures were observed to be complicated. Elastic and plastic deformations, unit cell expansion, composition, components, crystallinities, and deformations have been reported as factors in the mechanism of hysteresis. (41−46) In this study, Mg may be attributed to negligible hysteresis because YCo3 without Mg exhibits hysteresis between the hydrogen absorption and desorption reactions (Figure S6 in the Supporting Information).

Figure 5

Figure 5. Cycling between hydrogen absorption and desorption reactions on Y0.68Mg0.32Co3.00 at 303 K. (Top) The PCT curves of (blue) 3 cycles and (green) 100 cycles. (Bottom) X-ray diffraction patterns of before and after the cycling up to 100 cycles.

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From the crystal structure investigations of Y0.68Mg0.32Co3.00 during the hydrogen absorption reactions, the hydrogen storage capacities were related to the spaces and affinities between the metal element and hydrogen in the AB2 units. To understand the amount of hydrogen that can be stored in Y0.68Mg0.32Co3.00, hydrogen absorption reactions were observed above 1 GPa, where the hydrogen chemical potential could be dramatically increased. (31,32) This finding indicates the potential hydrogen storage capacity of Y0.68Mg0.32Co3.00. Figure 6 shows X-ray diffraction patterns obtained above 1 GPa at 473 K. In these experiments, the hydrogen source, BH3NH3, must first release hydrogen before the pressure is increased. At 473 K and 1 GPa, the Bragg peaks shift to larger d-spacings. This result indicated the release of hydrogen from the hydrogen source, hydrogen absorption reactions on Y0.68Mg0.32Co3.00, and the formation of Y0.68Mg0.32Co3.00 hydride. After confirming hydrogen release from the hydrogen sources and formation of Y0.68Mg0.32Co3.00 hydride, the temperature was decreased to room temperature, and hydrogen absorption reactions were observed at room temperature with increasing pressures for up to 10 GPa. Notably, the Bragg peak positions are mostly maintained in the X-ray diffraction patterns at room temperature and above 1 GPa, even though the pressure increases to 10 GPa (Figure 6), signifying that more hydrogen is stored in Y0.68Mg0.32Co3.00. The phenomenon, which shows higher hydrogen storage capacities above 1 GPa, was also reported in AB5-based alloys. (47,48) To estimate the amount of absorbed hydrogen in Y0.68Mg0.32Co3.00, the unit cell volumes per formula unit as a function of pressure (Figure 7) are considered, as reported for hydrogen absorption reactions on LaNi5 above 1 GPa. (47) In Figure 7, the unit cell volumes (V) per formula unit (Z) are obtained from high-pressure experiments with and without the hydrogen source. High-pressure experiments without a hydrogen source indicated the V/Z ratio of Y0.68Mg0.32Co3.00 under high pressure. From neutron diffraction experiments, the V/Z values of Y0.68Mg0.32Co3.00 and Y0.68Mg0.32Co3.00H3.76 were 522.51/9 = 58.06 Å3/f.u., and 618.72/9 = 68.75 Å3/f.u., respectively. Therefore, the volume of hydrogen atoms in Y0.68Mg0.32Co3.00H3.76 was estimated to be 10.69 Å3/f.u., where 2.84 Å3 was estimated to be the volume of one hydrogen atom. Although the unit cell volume per formula unit of Y0.68Mg0.32Co3.00H3.76 at 1–10 GPa cannot be experimentally observed, it is estimated from the volume of hydrogen atoms in Y0.68Mg0.32Co3.00H3.76 (10.69 Å3/f.u.) added to the volume per formula unit of Y0.68Mg0.32Co3.00 at 1–10 GPa (blue circles in Figure 7). In Figure 7, the gap between the V/Z of Y0.68Mg0.32Co3.00 with the hydrogen source and Y0.68Mg0.32Co3.00H3.76 can be the volume of hydrogen atoms stored under high pressure. As mentioned above, the volume of one hydrogen atom was 2.84 Å3, highlighting that the chemical formula at 10 GPa could be Y0.68Mg0.32Co3.00H7.19, for which the gravimetric hydrogen density reached 2.88 mass %. Figure 8 shows the relationship between hydrogen content and pressure combined with the PCT measurement at 303 K and the high-pressure experiment at room temperature. As mentioned in the section on the crystal structure, the AB5 unit (55.9%) with less Mg contained more D atoms than the AB2 unit (32.4%). This finding that more spaces in the AB2 units could be found in Y0.68Mg0.32Co3.00D3.76. We speculate that the spaces in the AB2 units would be related to increasing of hydrogen storage capacities in the higher-pressure region. This finding suggests that Y0.68Mg0.32Co3.00 has the potential to increase hydrogen storage capacity if the spaces and components of affinities to hydrogen can be optimized.

Figure 6

Figure 6. X-ray diffraction patterns of Y0.68Mg0.32Co3.00 at (bottom) 474 K at 1.6 GPa, and (top) room temperature from 1 to 10 GPa.

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Figure 7

Figure 7. Unit cell volume of Y0.68Mg0.32Co3.00 above 1 GPa at room temperature. In the figure, black and red circles are obtained from high-pressure experiments on Y0.68Mg0.32Co3.00 without and with hydrogen source, respectively. Blue circles are estimated unit cell volume of Y0.68Mg0.32Co3.00H3.67.

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Figure 8

Figure 8. Hydrogen contents in (Y, Mg)Co3 from 10–2 to 104 MPa.

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Data points from 10–2 to 101 MPa are obtained by PCT measurements (absorption) at 303 K. Data points from 103 to 104 MPa are estimated by high-pressure experiments at room temperature. Top axis indicates hydrogen and metal atomic ratio.

Conclusions

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The AB3-based alloy Y0.68Mg0.32Co3.00 was obtained from AB2 alloys, YCo2 and MgCo2, at 1172 K in an Ar atmosphere. The crystal structure and hydrogen absorption reactions of Y0.68Mg0.32Co3.00, before and after hydrogen absorption reactions, were investigated. Before hydrogen absorption reactions, the crystal structure of Y0.68Mg0.32Co3.00 with a = 4.99894(6) Å and c = 24.18914(45) Å in the space group R3̅m (No. 166) was found to be composed of a Laves polyhedra (AB2 units) and capped hexagonal prisms (AB5 units). In the crystal structure, Mg atoms were located at two crystallographically different atomic positions at the centers of the AB2 and AB5 units. In addition, the atomic positions of the Mg were the same as those of the Y atoms with different occupancies. Only the occupancies of the Mg atoms in the AB2 units increased, although the amount of Mg increased. This finding indicates that the excess Mg atoms are likely to be located on the AB2 unit side. In the hydrogen absorption reactions, the crystal structure motif of Y0.68Mg0.32Co3.00 was maintained. The atomic positions of hydrogen were identified, and their occupations were refined using neutron diffraction under a D2 pressure of 5 MPa at 323 K. In the crystal structure, the D atoms were located at five crystallographically different atomic positions. Two D atoms were located at the interunit positions (between the AB2 and AB5 units), two D atoms were located at the intra-AB2 unit positions (inside the AB2 unit), and one D atom was located at the intra-AB5 unit positions (inside the AB5 unit).
Y0.68Mg0.32Co3.00 exhibited reversible hydrogen absorption and desorption reactions with a hydrogen storage capacity of 1.68 mass % at 303 K below 10 MPa and minimal degradation for up to 100 cycles of hydrogen absorption and desorption reactions. The hydrogen storage capacity of Y0.68Mg0.32Co3.00 was higher than that of LaNi5 (1.38 mass %), an industrially used hydrogen storage base material. The hydrogen storage capacity and equilibrium hydrogen absorption and desorption reaction pressures depend on the amount of Mg. In particular, excess Mg atoms were located in the AB2 units of the crystal structure. As the hydrogen storage capacities and equilibrium hydrogen absorption and desorption reaction pressures depend on the amount of Mg preferred by the AB2 units, the hydrogen storage properties were controlled by the spaces and affinities of the AB2 units. Considering the fraction of D atoms in the inter-, intra-AB2, and intra-AB5 units, spaces existed in the AB2 units.
To investigate the maximum hydrogen storage capacity of Y0.68Mg0.32Co3.00, hydrogen absorption reactions were investigated at pressures above 1 GPa, at which the chemical potential of hydrogen dramatically increased. The hydrogen storage capacity finally increased to 2.88 mass % at 10 GPa at room temperature. This finding shows the potential of further site occupation by hydrogen in Y0.68Mg0.32Co3.00 to increase hydrogen storage capacity.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.4c06759.

  • X-ray diffraction patterns of the starting materials YCo2 and MgNi2; Rietveld refinement fits of synchrotron radiation X-ray diffraction and neutron diffraction; and crystallographic parameters (PDF)

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Author Information

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  • Corresponding Author
  • Authors
    • Hiroyuki Saitoh - National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan
    • Reina Utsumi - National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan
    • Jyunya Ito - Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
    • Kazuki Obana - Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan
    • Yuki Nakahira - National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan;  Orcidhttps://orcid.org/0000-0003-0241-0786
    • Denis Sheptyakov - Laboratory for Neutron Scattering and Imaging, PSI Center for Neutron and Muon Sciences, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
    • Takashi Honda - Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan;  Orcidhttps://orcid.org/0000-0003-4121-8957
    • Hajime Sagayama - Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
    • Shigeyuki Takagi - National Institutes for Quantum Science and Technology, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5148, Japan
    • Tatsuoki Kono - Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
    • Heena Yang - Water Energy Research Center, Korea Water Resources Corporation, 125 Yuseong-daero 1689beon-gil, Yuseong-gu, Daejeon 34045, Republic of Korea
    • Wen Luo - School of Environmental and Chemical Engineering, Shanghai University, Shangda Road 99, 200444 Shanghai, China;  Orcidhttps://orcid.org/0000-0003-4250-6168
    • Loris Lombardo - Laboratory of Materials for Renewable Energy (LMER), Institute of Chemical Sciences and Engineering (ISIC), Basic Science Faculty (SB), École Polytechnique Fédérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Rue de l’Industrie 17, CH-1951 Sion, Switzerland;  Empa Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland;  Orcidhttps://orcid.org/0000-0003-2968-6686
    • Andreas Züttel - Laboratory of Materials for Renewable Energy (LMER), Institute of Chemical Sciences and Engineering (ISIC), Basic Science Faculty (SB), École Polytechnique Fédérale de Lausanne (EPFL) Valais/Wallis, Energypolis, Rue de l’Industrie 17, CH-1951 Sion, Switzerland;  Empa Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
    • Shin-ichi Orimo - Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan;  Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
  • Author Contributions

    T.S. conceived this study, prepared and evaluated the samples, performed synchrotron radiation X-ray diffraction, and hydrogen storage properties, analyzed the data, and wrote the manuscript. H.S., R.U., J.I., K.O., and Y.N. performed high-pressure experiments above 1 GPa. D.S. performed neutron diffraction. W.L. prepared the sample for neutron diffraction. T.H. and H.S. performed synchrotron radiation X-ray diffraction. S.T., T.K., H.Y., W.L., L.L., A.Z., and S.O. participated and discussed the results.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This research was supported by JST SICORP (JPMJSC 1802), MEXT/JSPS KAKENHI (23K23085, 22H01817, JP18H05513 (“Hydrogenomics”), 19K05051), GteX Program Japan Grant Number JPMJGX23H1, and the GIMRT Program of the Institute for Materials Research, Tohoku University (Proposal No. 202106-RDKGE-0102, 202112-RDKGE-0012, 202212-RDKGE-0039). Synchrotron powder X-ray diffraction was approved by the Photon Factory Program Advisory Committee (Proposal No. 2019G572). Synchrotron X-ray radiation experiments at SPring-8 were supported by the QST Advanced Characterization Nanotechnology Platform under the remit of the Nanotechnology Platform of the Ministry of Education, Culture, Sports, Science, and Technology MEXT, Japan (Proposal Nos. JPMXP09A21QS0031, JPMXP1222QS0007, and JPMXP1222QS0117). The synchrotron radiation X-ray diffraction experiments were performed using a QST experimental station at the QST beamline BL14B1 and SPring-8, with the approval of the Japan Synchrotron Radiation Research Institute JASRI (Proposal Nos. 2021B3694, 2022A3694, and 2022B3694). This work is partly based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland (Proposal No.: 20202035)

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    The title compds. were prepd. by induction melting and studied with respect to structure and hydrogenation properties. Both crystallize with the cubic MgCu4Sn type structure (space group F43m, LaNi4Mg: a = 7.17-7.18 Å, NdNi4Mg: a = 7.09875(1) Å) and absorb reversibly up to 4 H atoms per formula unit at 7-8 bar and ∼50°. Synchrotron and neutron powder diffraction data on deuterated NdNi4Mg indicate an orthorhombic lattice distortion (NdNi4MgD3.6, space group Pmn21, a 5.0767(2), b 5.4743(2), c 7.3792(3) Å, ΔV/V = 14.6%) and three almost fully occupied D sites of which two are coordinated by a trigonal metal bipyramid ([A2B3] apexes: A = 2Nd, base: B = 2Ni,Mg) and one is coordinated by a metal tetrahedron ([AB3] A = Nd, B = 3Ni). The hydride is stable at room temp. under 1 bar H pressure, but desorbs rapidly at 80° under vacuum. Under air it decomps. by catalytic H2O formation.
  18. 18
    Terashita, N.; Akiba, E. Hydriding Properties of (Mg1–xMx)Ni2 C15-Type Laves Phase Alloys. Mater. Trans. 2006, 47, 1890– 1893,  DOI: 10.2320/matertrans.47.1890
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    Hydriding properties of (Mg1-xMx)Ni2 C15-type Laves phase alloys
    Terashita, Naoyoshi; Akiba, Etsuo
    Materials Transactions (2006), 47 (8), 1890-1893CODEN: MTARCE; ISSN:1345-9678. (Japan Institute of Metals)
    Mg-based Laves phase alloys, (Mg0.7M0.3)Ni2, where M is Ca, La, Ce, Pr, Nd or Gd were prepd. The alloys can be synthesized by conventional induction melting and annealing using intermetallic compds. MgNi2 and MNi2 as a source of Mg, Ni and M. The crystal structures of the major phases of annealed (Mg0.7M0.3)Ni2 alloys were C15-type for M = Ca and C15b-type for M = La, Ce, Pr, Nd and Gd Laves structures, resp. In all alloys, except M = Ce, hydrogenation and dehydrogenation occurred reversibly. The max. H contents of the alloys are 1.2-1.6% (H/M:0.6-0.8) under a H pressure of 5 MPa at 243-273 K. As the results of measurements of P-C isotherms, in the case of M = Pr and Nd, 2 step plateaus were obsd. After a few hydrogenation/dehydrogenation cycles the alloys retained C15-type or C15b-type Laves structures without H-induced amorphization, disproportionation and decompn.
  19. 19
    Chotard, J.-N.; Sheptyakov, D.; Yvon, K. Hydrogen Induced Site Depopulation in the LaMgNi4–Hydrogen System. Z. Kristallogr. 2008, 223, 690– 696,  DOI: 10.1524/zkri.2008.1124
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    Hydrogen induced site depopulation in the LaMgNi4-hydrogen system
    Chotard, Jean-Noel; Sheptyakov, Denis; Yvon, Klaus
    Zeitschrift fuer Kristallographie (2008), 223 (10), 690-696CODEN: ZEKRDZ; ISSN:0044-2968. (Oldenbourg Wissenschaftsverlag GmbH)
    The LaMgNi4-H system was studied by in-situ neutron powder diffraction and pressure-compn. isotherm measurements at 100° and H(D) pressures of up 50 bar. The system displays three hydride phases that have distinctly different H plateau pressures and H atom distributions. The cubic α-LaMgNi4H0.75 phase forms <0.01 bar H pressure and H atoms fill one type of tetrahedral Ni4 interstices. The orthorhombic distorted β-LaMgNiH3.7 phase forms at ∼3 bar H pressure and H atoms fill both tetrahedral LaNi3 and triangular bi-pyramidal La2MgNi2 interstices. Tetrahedral Ni4 interstices are no longer occupied. Finally, the most H rich γ-LaMgNi4H4.85 phase forms >20 bar. It has again cubic symmetry and H atoms continue to occupy triangular bipyramidal La2MgNi2 interstices while filling a new type of tetrahedral Ni4 interstices that are neither occupied in the α- nor in the β-phase. The tetrahedral LaNi3 interstices occupied in the β-phase are empty. H induced depopulations of interstitial sites in metal hydrides are relatively rare and consistent with, but not entirely due to, the onset of repulsive H-H interactions at increasing H concns. Crystallog. data and at. coordinates are given.
  20. 20
    Denys, R. V.; Riabov, A. B.; Černý, R.; Koval’chuk, I. V.; Zavaliy, I. Yu. New CeMgCo4 and Ce2MgCo9 Compounds: Hydrogenation Properties and Crystal Structure of Hydrides. J. Solid State Chem. 2012, 187, 1– 6,  DOI: 10.1016/j.jssc.2011.10.040
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    New CeMgCo4 and Ce2MgCo9 compounds. Hydrogenation properties and crystal structure of hydrides
    Denys, R. V.; Riabov, A. B.; Cerny, R.; Koval'chuk, I. V.; Zavaliy, I. Yu.
    Journal of Solid State Chemistry (2012), 187 (), 1-6CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
    Two new ternary intermetallic compds., CeMgCo4 (C15b pseudo-Laves phase, MgCu4Sn type) and Ce2MgCo9 (substitution deriv. of PuNi3 type) were synthesized by mech. alloying method. The structural and hydrogenation properties of these compds. were studied by x-ray diffraction and Pressure-Compn.-Temp. measurements. Both compds. absorb hydrogen at room temp. and pressures below 10 MPa forming hydrides with max. compns. CeMgCo4H6 and Ce2MgCo9H12. Single plateau behavior was obsd. in P-C isotherm during H absorption/desorption by Ce2MgCo9 alloy. The CeMgCo4-H2 system is characterized by the presence of 2 absorption/desorption plateaus corresponding to formation of β-CeMgCo4H4 and γ-CeMgCo4H6 hydride phases. The structure of β-hydride CeMgCo4H(D)4 was detd. from x-ray and neutron powder diffraction data. In this structure initial cubic symmetry of CeMgCo4 is preserved and hydrogen atoms fill only one type of interstitial sites, triangular MgCo2 faces. These positions are occupied by 70% and form octahedron around Mg atom with Mg-D bond distances 1.84 Å.
  21. 21
    Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E. In Situ X–ray Diffraction Study of Phase Transformation of Mg2–xPrxNi4 during Hydrogenation and Dehydrogenation (x = 0.6 and 1.0). J. Phys. Chem. C 2012, 116, 1401– 1407,  DOI: 10.1021/jp206446c
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    In Situ X-ray Diffraction Study of Phase Transformation of Mg2-xPrxNi4 during Hydrogenation and Dehydrogenation (x = 0.6 and 1.0)
    Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E.
    Journal of Physical Chemistry C (2012), 116 (1), 1401-1407CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The phase transformations of Mg1.4Pr0.6Ni4 and Mg1.0Pr1.0Ni4 during hydrogenation and dehydrogenation have been investigated using in situ X-ray diffraction (XRD). Both alloys showed the cubic MgCu4Sn type structure with space group F‾43m before hydrogenation. The hydride β-Mg1.4Pr0.6Ni4H∼3.6 had the same crystal structure as the starting alloy, and its lattice was expanded by 4.3% by hydrogenation. Mg1.0Pr1.0Ni4 was initially transformed to an orthorhombic β-Mg1.0Pr1.0Ni4H∼4 with space group Pmn21. By further hydrogenation, the orthorhombic hydride changed to γ-Mg1.0Pr1.0Ni4H∼6 with a cubic structure with space group F‾43m. The lattice const. of γ-Mg1.0Pr1.0Ni4H∼6 was 7.6% larger than that of the starting alloy. Through dehydrogenation, all hydride phases returned to the alloy phase without any amorphization or disproportionation.
  22. 22
    Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E. Effect of Rare Earth Elements and Alloy Composition on Hydrogenation Properties and Crystal Structures of Hydrides in Mg2–xRExNi4. J. Phys. Chem. C 2012, 116, 19156– 19163,  DOI: 10.1021/jp3052856
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    22
    Effect of Rare Earth Elements and Alloy Composition on Hydrogenation Properties and Crystal Structures of Hydrides in Mg2-xRExNi4
    Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E.
    Journal of Physical Chemistry C (2012), 116 (36), 19156-19163CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The effect of the rare earth elements and alloy compn. on the hydrogenation properties and crystal structures of hydrides in Mg2-xRExNi4 (RE = La, Pr, Nd, Sm, and Gd; x = 0.6 and 1.0) was investigated. All Mg2-xRExNi4 alloys had a C15b Laves phase before hydrogenation. Mg1.4RE0.6Ni4 (RE = Pr, Sm, and Gd) alloys were hydrogenated through one plateau to form Mg1.4RE0.6Ni4H∼3.6 while maintaining the C15b structure. Mg1.0RE1.0Ni4 (RE = La, Pr, and Nd) alloys were hydrogenated to ∼1.0 H/M proceeding through two plateaus, and Mg1.0RE1.0Ni4 (RE = Sm and Gd) alloys were hydrogenated to 0.6-0.7 H/M through one plateau. Mg1.0RE1.0Ni4 alloys initially transformed into Mg1.0RE1.0Ni4H∼4 with an orthorhombic structure. In addn. it was exptl. confirmed that Mg1.0RE1.0Ni4H∼4 with La, Pr, and Nd transformed into Mg1.0RE1.0Ni4H∼6 with a C15b structure, while no formation of Mg1.0RE1.0Ni4H∼6 (RE = Sm and Gd) was obsd. at 40 MPa at 250 K. Theor. calcns. suggest that Mg1.0RE1.0Ni4H∼4 with Sm and Gd also transform to Mg1.0RE1.0Ni4H∼6 at higher pressures than those used in our expts. (264 MPa for Mg1.0Sm1.0Ni4 and 8.5 GPa for Mg1.0Gd1.0Ni4 at 253 K). The hydrogenation properties and crystal structure of the hydrides in Mg2-xRExNi4 are dependent on the alloy compn., i.e., the ratio of Mg to RE in the alloy phase, but independent of the choice of rare earth element.
  23. 23
    Sakaki, K.; Terashita, N.; Kim, H.; Proffen, T.; Majzoub, E. H.; Tsunokake, S.; Nakamura, Y.; Akiba, E. Crystal Structure and Local Structure of Mg2-xPrxNi4 (x = 0.6 and 1.0) Deuteride Using in Situ Neutron Total Scattering. Inorg. Chem. 2013, 52, 7010– 7019,  DOI: 10.1021/ic400528u
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    Crystal Structure and Local Structure of Mg2-xPrxNi4 (x = 0.6 and 1.0) Deuteride Using in Situ Neutron Total Scattering
    Sakaki, K.; Terashita, N.; Kim, H.; Proffen, T.; Majzoub, E. H.; Tsunokake, S.; Nakamura, Y.; Akiba, E.
    Inorganic Chemistry (2013), 52 (12), 7010-7019CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
    The authors studied crystal structure and local structure of Mg2-xPrxNi4 (x = 0.6 and 1.0) and their deuterides using in situ neutron total scattering and 1st-principles calcns. The total scattering data were analyzed using Rietveld refinement and pair distribution function anal. (PDF). The crystal structure of Mg2-xPrxNi4 before D absorption was C15b in space group F4-3m. Crystallog. data and at. coordinates are given. No difference between the crystal and local (PDF) structures was obsd. The crystal structure of Mg1.0Pr1.0Ni4D∼4 is orthorhombic in space group Pmn21, with three D occupation sites: PrNi3 and two types of bipyramidal Pr2MgNi2 that have a plane of symmetry composed of MgNi2. There is no significant difference between the crystal structure and the local structure of Mg1.0Pr1.0Ni4D∼4. However, the av. crystal structure of the Mg-rich Mg1.4Pr0.6Ni4D∼3.6 was C15b with two D occupation sites: PrNi3 and MgPrNi2 suggesting that the D occupation shifts away from the Pr2MgNi2 bipyramid. First-principles relaxed structures also showed the shift of the H occupation site toward the Pr atom of the bipyramid, when induced by Mg substitution for the opposing Pr, resulting in H occupation in the MgPrNi2 tetrahedral site. The PDF pattern of Mg1.4Pr0.6Ni4D∼3.6 cannot be refined <7.2 Å in at. distances using the C15b structure which was obtained from Rietveld refinement but can be done using an orthorhombic structure. Probably Mg1.4Pr0.6Ni4D∼3.6 was locally distorted to the orthorhombic.
  24. 24
    Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Riabov, A. B.; Zavaliy, I. Yu. Hydrogenation Properties and Crystal Structure of YMgT4 (T = Co, Ni, Cu) Compounds. J. Alloys Compd. 2014, 603, 7– 13,  DOI: 10.1016/j.jallcom.2014.03.030
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    Hydrogenation properties and crystal structure of YMgT4 (T = Co, Ni, Cu) compounds
    Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Riabov, A. B.; Zavaliy, I. Yu.
    Journal of Alloys and Compounds (2014), 603 (), 7-13CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    New two ternary YMgCo4 and YMgCu4 and one quaternary YMgCo2Ni2 compds. were synthesized by mech. alloying with further annealing. The hydrogenation capacity of YMgCo4 reaches 6.8 at.H/f.u. The Pressure-Compn.-Temp. studies of YMgCo4-H2 and YMgNi4-H2 systems revealed that introduction of magnesium, accompanied by shrinking of the unit cell, decreases the stability of hydrides comparing to binary YCo2 and YNi2 compds. The values of heat and entropy of the YMgCo4H6.8 hydride formation were calcd.: ΔH = -27.9 ± 0.8 kJ mol-1 H2 and ΔS = -93.4 ± 2.6 J mol-1 H2 K-1. The YMgCo2Ni2-H2 system shows intermediate thermodn. properties compared to the ternary hydrides (ΔH = -28.8 ± 0.2 kJ mol-1 H2 and ΔS = -117.6 ± 2.4 J mol-1 H2 K-1). The YMgCo4H6.8 and YMgCo2Ni2H4.9 hydrides keep the cubic structure of the parent compds. with a cell vol. expansion of 23 and 14.4% resp. The YMgCu4 compd. does not interact with hydrogen under normal conditions.
  25. 25
    Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Verbovytskyy, Yu. V; Zavaliy, I. Yu. Effect of Co Substitution on Hydrogenation and Magnetic Properties of NdMgNi4 Alloy. J. Alloys Compd. 2015, 639, 526– 532,  DOI: 10.1016/j.jallcom.2015.03.187
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    Effect of Co substitution on hydrogenation and magnetic properties of NdMgNi4 alloy
    Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Verbovytskyy, Yu. V.; Zavaliy, I. Yu.
    Journal of Alloys and Compounds (2015), 639 (), 526-532CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
    The influence of Co substitution on the structural and magnetic properties of NdMgNi4-xCox (x ≤ 3) alloys and their hydrides was investigated. The formation of NdMgCo4 compd. has not been obsd. The gas hydrogenation of these alloys resulted in the formation of NdMgNi4H4, NdMgNi3CoH4.8, NdMgNi2Co2H5.6 and NdMgNiCo3H6.2 hydrides. Transformation from cubic into orthorhombic structure upon hydrogenation was confirmed for NdMgNi4H4 hydride, whereas Co-contg. hydrides preserved the parent cubic structure. PC diagrams at 50° for NdMgNi4-xCox-H2 (x = 0, 2, 3) showed only one absorption/desorption plateau, which equil. pressure decrease as the cell vol. increase. The NdMgCu4 ternary compd. was synthesized, but it does not interact with hydrogen under normal conditions. Electrochem. investigations demonstrated that substitution of the nickel atoms by the cobalt ones in NdMgNi4 does not significantly influence on the max. discharge capacity (244-261 mA h/g) and all alloys are characterized by high cyclic stability. NdMgNi4 and its hydride display a Pauli paramagnet behavior. NdMgNi2Co2 displays a magnetic order below 50 K whereas its hydride shows a Pauli paramagnet behavior similar to that of NdMgNi4H4.
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    Shtender, V. V.; Denys, R. V.; Zavaliy, I.Yu.; Zelinska, O. Ya.; Paul-Boncour, V.; Pavlyuk, V. V. Phase Equilibria in the Tb-Mg-Co System at 500 °C, Crystal Structure and Hydrogenation Properties of Selected Compounds. J. Solid State Chem. 2015, 232, 228– 235,  DOI: 10.1016/j.jssc.2015.09.031
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    Phase equilibria in the Tb-Mg-Co system at 500 °C, crystal structure and hydrogenation properties of selected compounds
    Shtender, V. V.; Denys, R. V.; Zavaliy, I. Yu.; Zelinska, O. Ya.; Paul-Boncour, V.; Pavlyuk, V. V.
    Journal of Solid State Chemistry (2015), 232 (), 228-235CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
    The isothermal section of the Tb-Mg-Co phase diagram at 500° was built on the basis of x-ray diffraction anal. of forty samples prepd. by powder metallurgy. The existence of two ternary compds. Tb4Mg3Co2 and Tb4MgCo was confirmed. The formation of two solid solns., Tb1-xMgxCo3 (0≤x≤0.4) and Tb1--xMgxCo2 (0≤x≤0.6), was found for the first time. Tb5Mg24 also dissolves a small amt. of Co. Other binary compds. do not dissolve the third component. The Tb4MgCo and TbMgCo4 compds. form hydrides (12.7 and 5.3 at.H/f.u. capacity, resp.) that retain the original structure of metallic matrixes. Upon thermal desorption the Tb4MgCoH12.7 hydride was stable up to 300° and disproportionated at higher temp. Two other hydrides, Tb4Mg3Co2H4 and Tb2MgCo9H12, are unstable in air and decomp. into the initial compds.
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    Yang, T.; Yuan, Z.; Bu, W.; Jia, Z.; Qi, Y.; Zhang, Y. Effect of Elemental Substitution on the Structure and Hydrogen Storage Properties of LaMgNi4 Alloy. Mater. Des. 2016, 93, 46– 52,  DOI: 10.1016/j.matdes.2015.12.150
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    Effect of elemental substitution on the structure and hydrogen storage properties of LaMgNi4 alloy
    Yang, Tai; Yuan, Zeming; Bu, Wengang; Jia, Zhichao; Qi, Yan; Zhang, Yanghuan
    Materials & Design (2016), 93 (), 46-52CODEN: MADSD2; ISSN:0264-1275. (Elsevier Ltd.)
    Intermetallic compds. with the nominal formula LaMgNi3.6M0.4 (M = Ni, Co, Mn, Cu, Al) were prepd. through induction melting, and the structure and hydrogen storage properties of the resultant alloys were extensively investigated. Results showed that the alloys exhibit sizable hydrogen absorption capacity and that elemental substitution significantly influences their microstructure and hydrogen storage properties. The discharge capacities of the alloy electrodes decrease in the order Co > Ni > Al > Cu > Mn. Moreover, the electrochem. kinetics of the alloys depend on their microstructures and phase compns. Smaller grain size is helpful to improve the electrochem. kinetics. The gaseous hydrogen absorption capacities of the alloys are approx. 1.7 wt.% in the first hydrogenation process. Cracking caused by hydrogenation and dehydrogenation also significantly improves the hydrogen absorption kinetics of the alloy particles. The hydrogen storage capacities of the alloys rapidly decrease with increasing cycle no. This result is attributed to amorphisation of the LaMgNi4 phase during hydrogen absorption-desorption cycling (H2-induced amorphisation). Our findings provide new insights into the capacity degrdn. mechanism of La-Mg-Ni system hydrogen storage alloys that may improve their cycling stability.
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    Shtender, V. V.; Paul-Boncour, V.; Denys, R. V.; Crivello, J.-C.; Zavaliy, I. Yu. TbMgNi4-xCox-(H,D)2 System. I: Synthesis, Hydrogenation Properties, and Crystal and Electronic Structures. J. Phys. Chem. C 2020, 124, 196– 204,  DOI: 10.1021/acs.jpcc.9b10252
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    TbMgNi4-xCox-(H,D)2 System. I: Synthesis, Hydrogenation Properties, and Crystal and Electronic Structures
    Shtender, Vitalii V.; Paul-Boncour, Valerie; Denys, Roman V.; Crivello, Jean-Claude; Zavaliy, Ihor Yu.
    Journal of Physical Chemistry C (2020), 124 (1), 196-204CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    A series of cubic TbMgNi4-xCox (x = 0-4) pseudo-binary compds. have been synthesized by either a solid-state reaction or mech. alloying with further annealing treatment. Their hydrogenation properties have been studied by pressure-compn.-temp. (PCT) measurements, showing the formation of α-, β-, and γ-hydrides. The Co for Ni substitution yields a lowering of the equil. pressure and an increase of the hydrogen capacity. An improvement of the kinetics of hydrogen absorption was obsd. with an increasing Co content. β-TbMgNi4-xCoxH∼4 (x = 0-3) hydrides show an orthorhombic distortion (Pmn21 space group), whereas the β-TbMgCo4H3.3 hydride crystallizes in a monoclinic structure (Pm space group) derived from the orthorhombic structure. Sensitivity of the formation of the β-TbMgCo4H3.3 hydride to temp. has been obsd. in PCT curves to exist below 50°C. γ-TbMgNi4-xCoxHy (x = 2-4, y > 5) hydrides preserve the parent cubic structure (F‾43m space group) with a hydrogen-induced vol. expansion of 17.9-22.3%. The deuterium for hydrogen substitution in the TbMgNiCo3-(H,D)2 system prevents fast desorption at room temp. and ambient pressure. The positions of deuterium atoms in the γ-TbMgCo4D6 deuteride were detd. by neutron powder diffraction. Two types of interstitial sites were found to be occupied: 87% of deuterium atoms (D1 site) are located inside Tb2MgCo2 octahedra and the remaining 13% (D2 site) are inside Co4 tetrahedra. The increase of the Co content allows the improvement of the thermodn. stability of TbMgNi4-xCox hydrides, as demonstrated by the lowering of the desorption plateau pressure, the increase of the desorption temp., and the increase of the enthalpy of formation vs. the Co content. This last exptl. result is confirmed by first-principles calcns. where electronic structures of intermetallic compds. and their cubic TbMgNi4-xCoxH6 hydrides are compared for x = 0, 2, and 4.
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    Solubility of hydrogen in metals under high hydrogen pressures: thermodynamical calculations
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    Acta Metallurgica et Materialia (1992), 40 (9), 2327-36CODEN: AMATEB; ISSN:0956-7151.
    The soly. of H was calcd. up to high H pressures for ten metals having small solubilities under normal pressures. The equation of state of H was calcd. by the procedure of H. Hemmes et al. (1986), and the values obtained for the molar volume, enthalpy, Gibbs free energy, and entropy are tabulated in the range 0.1-100 GPa and 400-2000 K. For soly. calcns., the chem. potential of H in solid soln. was detd. The solubilities obtained for fcc. metals Al, γ-Fe, Ni, Cu, Ag, Pt, Au and bcc. metals Cr, α-Fe, Mo, W are shown in the form of Arrhenius relations with pressure as a parameter. Strong enhancements of the soly. over Sieverts law were found at high H pressures ≥1 GPa.
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    An indexing program, TREOR, mainly based on trial-and-error methods, is described. The program contains sep. routines for cubic, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic symmetries. Ten years usage was analyzed to improve the original program. For monoclinic indexing, a specific short-axis test was developed. The over-all success rate of the program is >90%, and considerably more for orthorhombic and higher symmetries.
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    A description and justification of the EXPGUI program is presented. This program implements a graphical user interface and shell for the GSAS (Generalized Structure and Anal. Software) single-crystal and Rietveld package. Use of the Tcl/Tk scripting language allows EXPGUI to be platform independent. Also included is a synopsis of how the program is implemented.
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  • Abstract

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    Figure 1

    Figure 1. Crystal structures of AB2, AB3, and AB5. In the crystal structure, A and B atoms are represented as gray and green spheres, respectively. Capped hexagonal prism and Laves polyhedra are represented as orange and green polyhedra, respectively.

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    Figure 2

    Figure 2. X-ray diffraction patterns of (Y, Mg)Co3 synthesized from (2–x)YCo2 + xMgCo2 (x = 0.8 and 1.0), and YCo3. In the figure, allow indicates Y2O3. Si was added as an internal standard.

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    Figure 3

    Figure 3. Crystal structures of (a) Y0.68Mg0.32Co3.00, and (b) Y0.68Mg0.32Co3.00D3.76. Y, Mg, Co, and D atoms are represented as gray, orange, green, and blue spheres, respectively. Y1/Mg1 surrounded by 18 Co atoms, and Y2/Mg2 surrounded by 12 Co atoms, are represented by orange and green polyhedra, respectively.

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    Figure 4

    Figure 4. Pressure–composition isotherm (PCT) curves of (black) Y0.68Mg0.32Co3.00 and (gray) Y0.58Mg0.42Co3.00 at 323 K. Closed and open circles indicate hydrogen absorption and desorption, respectively. The PCT curves in the figure are obtained in the third run.

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    Figure 5

    Figure 5. Cycling between hydrogen absorption and desorption reactions on Y0.68Mg0.32Co3.00 at 303 K. (Top) The PCT curves of (blue) 3 cycles and (green) 100 cycles. (Bottom) X-ray diffraction patterns of before and after the cycling up to 100 cycles.

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    Figure 6

    Figure 6. X-ray diffraction patterns of Y0.68Mg0.32Co3.00 at (bottom) 474 K at 1.6 GPa, and (top) room temperature from 1 to 10 GPa.

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    Figure 7

    Figure 7. Unit cell volume of Y0.68Mg0.32Co3.00 above 1 GPa at room temperature. In the figure, black and red circles are obtained from high-pressure experiments on Y0.68Mg0.32Co3.00 without and with hydrogen source, respectively. Blue circles are estimated unit cell volume of Y0.68Mg0.32Co3.00H3.67.

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    Figure 8

    Figure 8. Hydrogen contents in (Y, Mg)Co3 from 10–2 to 104 MPa.

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      The Crystal Structures in Hydrogen Absorption Reactions of REMgNi4-Based Alloys (RE: Rare-Earth Metals)
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      Energies (Basel, Switzerland) (2021), 14 (23), 8163CODEN: ENERGA; ISSN:1996-1073. (MDPI AG)
      A review. REMgNi4-based alloys, RE(2-x)MgxNi4 (RE: rare-earth metals; 0 < x < 2), with a AuBe5-type crystal structure, exhibit reversible hydrogen absorption and desorption reactions, which are known as hydrogen storage properties. These reactions involve formation of three hydride phases. The hydride formation pressures and hydrogen storage capacities are related to the radii of the RE(2-x)MgxNi4, which in turn are dependent on the radii and compositional ratios of the RE and Mg atoms. The crystal structures formed during hydrogen absorption reactions are the key to understanding the hydrogen storage properties of RE(2-x)MgxNi4. Therefore, in this review, we provide an overview of the crystal structures in the hydrogen absorption reactions focusing on RE(2-x)MgxNi4.
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      Structural determination of AMgNi4 (where A=Ca, La, Ce, Pr, Nd and Y) in the AuBe5 type structure
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      A no. of new ternary magnesium based alloys AMgNi4 (where A=Ca, La, Ce, Pr, Nd, and Y) have been synthesized by direct combination of the elements in the at. ratio A:Mg:Ni=1:1:4. The crystal structures were detd. by Guinier-Hagg X-ray powder diffraction. The compds. have a cubic SnMgCu4 (AuBe5 type) structure, which is related to the (C15) MgCu2 structure. All interat. distances indicate metallic-type bonding.
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      Structural and hydriding properties of MgYNi4: a new intermetallic compound with C15b-type Laves phase structure
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      A new intermetallic compd. MgYNi4 with C15b(AuBe5)-type Laves phase structure was successfully synthesized by both mech. milling and casting methods. The structural and hydriding properties of the samples were examd. by X-ray diffraction measurement, thermal anal. and hydrogen pressure-compn. (p-c) isotherm measurement. The lattice parameter of MgYNi4 was estd. to be a = 0.701 nm, which is ca. 2% smaller than that of YNi2. A plateau (miscibility-gap) pressure was clearly obsd. in the p-c isotherm during the dehydriding process of the sample synthesized by casting. The max. hydrogen content is ∼ 1.05 mass% (H/M ∼ 0.6) under a hydrogen pressure of 4.0 MPa at 313 K, and the enthalpy of hydride formation was calcd. to be -35.8 kJ/mol H2. The study in this paper reveals, for the first time, an application potential of MgNi2-based Laves phase structure for practical use as hydrogen storage and transport materials.
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      Guénée, L.; Favre-Nicolin, V.; Yvon, K. Synthesis, Crystal Structure and Hydrogenation Properties of the Ternary Compounds LaNi4Mg and NdNi4Mg. J. Alloys Compd. 2003, 348, 129– 137,  DOI: 10.1016/S0925-8388(02)00797-1
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      Synthesis, crystal structure and hydrogenation properties of the ternary compounds LaNi4Mg and NdNi4Mg
      Guenee, L.; Favre-Nicolin, V.; Yvon, K.
      Journal of Alloys and Compounds (2003), 348 (1-2), 129-137CODEN: JALCEU; ISSN:0925-8388. (Elsevier Science B.V.)
      The title compds. were prepd. by induction melting and studied with respect to structure and hydrogenation properties. Both crystallize with the cubic MgCu4Sn type structure (space group F43m, LaNi4Mg: a = 7.17-7.18 Å, NdNi4Mg: a = 7.09875(1) Å) and absorb reversibly up to 4 H atoms per formula unit at 7-8 bar and ∼50°. Synchrotron and neutron powder diffraction data on deuterated NdNi4Mg indicate an orthorhombic lattice distortion (NdNi4MgD3.6, space group Pmn21, a 5.0767(2), b 5.4743(2), c 7.3792(3) Å, ΔV/V = 14.6%) and three almost fully occupied D sites of which two are coordinated by a trigonal metal bipyramid ([A2B3] apexes: A = 2Nd, base: B = 2Ni,Mg) and one is coordinated by a metal tetrahedron ([AB3] A = Nd, B = 3Ni). The hydride is stable at room temp. under 1 bar H pressure, but desorbs rapidly at 80° under vacuum. Under air it decomps. by catalytic H2O formation.
    18. 18
      Terashita, N.; Akiba, E. Hydriding Properties of (Mg1–xMx)Ni2 C15-Type Laves Phase Alloys. Mater. Trans. 2006, 47, 1890– 1893,  DOI: 10.2320/matertrans.47.1890
      18
      Hydriding properties of (Mg1-xMx)Ni2 C15-type Laves phase alloys
      Terashita, Naoyoshi; Akiba, Etsuo
      Materials Transactions (2006), 47 (8), 1890-1893CODEN: MTARCE; ISSN:1345-9678. (Japan Institute of Metals)
      Mg-based Laves phase alloys, (Mg0.7M0.3)Ni2, where M is Ca, La, Ce, Pr, Nd or Gd were prepd. The alloys can be synthesized by conventional induction melting and annealing using intermetallic compds. MgNi2 and MNi2 as a source of Mg, Ni and M. The crystal structures of the major phases of annealed (Mg0.7M0.3)Ni2 alloys were C15-type for M = Ca and C15b-type for M = La, Ce, Pr, Nd and Gd Laves structures, resp. In all alloys, except M = Ce, hydrogenation and dehydrogenation occurred reversibly. The max. H contents of the alloys are 1.2-1.6% (H/M:0.6-0.8) under a H pressure of 5 MPa at 243-273 K. As the results of measurements of P-C isotherms, in the case of M = Pr and Nd, 2 step plateaus were obsd. After a few hydrogenation/dehydrogenation cycles the alloys retained C15-type or C15b-type Laves structures without H-induced amorphization, disproportionation and decompn.
    19. 19
      Chotard, J.-N.; Sheptyakov, D.; Yvon, K. Hydrogen Induced Site Depopulation in the LaMgNi4–Hydrogen System. Z. Kristallogr. 2008, 223, 690– 696,  DOI: 10.1524/zkri.2008.1124
      19
      Hydrogen induced site depopulation in the LaMgNi4-hydrogen system
      Chotard, Jean-Noel; Sheptyakov, Denis; Yvon, Klaus
      Zeitschrift fuer Kristallographie (2008), 223 (10), 690-696CODEN: ZEKRDZ; ISSN:0044-2968. (Oldenbourg Wissenschaftsverlag GmbH)
      The LaMgNi4-H system was studied by in-situ neutron powder diffraction and pressure-compn. isotherm measurements at 100° and H(D) pressures of up 50 bar. The system displays three hydride phases that have distinctly different H plateau pressures and H atom distributions. The cubic α-LaMgNi4H0.75 phase forms <0.01 bar H pressure and H atoms fill one type of tetrahedral Ni4 interstices. The orthorhombic distorted β-LaMgNiH3.7 phase forms at ∼3 bar H pressure and H atoms fill both tetrahedral LaNi3 and triangular bi-pyramidal La2MgNi2 interstices. Tetrahedral Ni4 interstices are no longer occupied. Finally, the most H rich γ-LaMgNi4H4.85 phase forms >20 bar. It has again cubic symmetry and H atoms continue to occupy triangular bipyramidal La2MgNi2 interstices while filling a new type of tetrahedral Ni4 interstices that are neither occupied in the α- nor in the β-phase. The tetrahedral LaNi3 interstices occupied in the β-phase are empty. H induced depopulations of interstitial sites in metal hydrides are relatively rare and consistent with, but not entirely due to, the onset of repulsive H-H interactions at increasing H concns. Crystallog. data and at. coordinates are given.
    20. 20
      Denys, R. V.; Riabov, A. B.; Černý, R.; Koval’chuk, I. V.; Zavaliy, I. Yu. New CeMgCo4 and Ce2MgCo9 Compounds: Hydrogenation Properties and Crystal Structure of Hydrides. J. Solid State Chem. 2012, 187, 1– 6,  DOI: 10.1016/j.jssc.2011.10.040
      20
      New CeMgCo4 and Ce2MgCo9 compounds. Hydrogenation properties and crystal structure of hydrides
      Denys, R. V.; Riabov, A. B.; Cerny, R.; Koval'chuk, I. V.; Zavaliy, I. Yu.
      Journal of Solid State Chemistry (2012), 187 (), 1-6CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
      Two new ternary intermetallic compds., CeMgCo4 (C15b pseudo-Laves phase, MgCu4Sn type) and Ce2MgCo9 (substitution deriv. of PuNi3 type) were synthesized by mech. alloying method. The structural and hydrogenation properties of these compds. were studied by x-ray diffraction and Pressure-Compn.-Temp. measurements. Both compds. absorb hydrogen at room temp. and pressures below 10 MPa forming hydrides with max. compns. CeMgCo4H6 and Ce2MgCo9H12. Single plateau behavior was obsd. in P-C isotherm during H absorption/desorption by Ce2MgCo9 alloy. The CeMgCo4-H2 system is characterized by the presence of 2 absorption/desorption plateaus corresponding to formation of β-CeMgCo4H4 and γ-CeMgCo4H6 hydride phases. The structure of β-hydride CeMgCo4H(D)4 was detd. from x-ray and neutron powder diffraction data. In this structure initial cubic symmetry of CeMgCo4 is preserved and hydrogen atoms fill only one type of interstitial sites, triangular MgCo2 faces. These positions are occupied by 70% and form octahedron around Mg atom with Mg-D bond distances 1.84 Å.
    21. 21
      Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E. In Situ X–ray Diffraction Study of Phase Transformation of Mg2–xPrxNi4 during Hydrogenation and Dehydrogenation (x = 0.6 and 1.0). J. Phys. Chem. C 2012, 116, 1401– 1407,  DOI: 10.1021/jp206446c
      21
      In Situ X-ray Diffraction Study of Phase Transformation of Mg2-xPrxNi4 during Hydrogenation and Dehydrogenation (x = 0.6 and 1.0)
      Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E.
      Journal of Physical Chemistry C (2012), 116 (1), 1401-1407CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The phase transformations of Mg1.4Pr0.6Ni4 and Mg1.0Pr1.0Ni4 during hydrogenation and dehydrogenation have been investigated using in situ X-ray diffraction (XRD). Both alloys showed the cubic MgCu4Sn type structure with space group F‾43m before hydrogenation. The hydride β-Mg1.4Pr0.6Ni4H∼3.6 had the same crystal structure as the starting alloy, and its lattice was expanded by 4.3% by hydrogenation. Mg1.0Pr1.0Ni4 was initially transformed to an orthorhombic β-Mg1.0Pr1.0Ni4H∼4 with space group Pmn21. By further hydrogenation, the orthorhombic hydride changed to γ-Mg1.0Pr1.0Ni4H∼6 with a cubic structure with space group F‾43m. The lattice const. of γ-Mg1.0Pr1.0Ni4H∼6 was 7.6% larger than that of the starting alloy. Through dehydrogenation, all hydride phases returned to the alloy phase without any amorphization or disproportionation.
    22. 22
      Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E. Effect of Rare Earth Elements and Alloy Composition on Hydrogenation Properties and Crystal Structures of Hydrides in Mg2–xRExNi4. J. Phys. Chem. C 2012, 116, 19156– 19163,  DOI: 10.1021/jp3052856
      22
      Effect of Rare Earth Elements and Alloy Composition on Hydrogenation Properties and Crystal Structures of Hydrides in Mg2-xRExNi4
      Sakaki, K.; Terashita, N.; Tsunokake, S.; Nakamura, Y.; Akiba, E.
      Journal of Physical Chemistry C (2012), 116 (36), 19156-19163CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The effect of the rare earth elements and alloy compn. on the hydrogenation properties and crystal structures of hydrides in Mg2-xRExNi4 (RE = La, Pr, Nd, Sm, and Gd; x = 0.6 and 1.0) was investigated. All Mg2-xRExNi4 alloys had a C15b Laves phase before hydrogenation. Mg1.4RE0.6Ni4 (RE = Pr, Sm, and Gd) alloys were hydrogenated through one plateau to form Mg1.4RE0.6Ni4H∼3.6 while maintaining the C15b structure. Mg1.0RE1.0Ni4 (RE = La, Pr, and Nd) alloys were hydrogenated to ∼1.0 H/M proceeding through two plateaus, and Mg1.0RE1.0Ni4 (RE = Sm and Gd) alloys were hydrogenated to 0.6-0.7 H/M through one plateau. Mg1.0RE1.0Ni4 alloys initially transformed into Mg1.0RE1.0Ni4H∼4 with an orthorhombic structure. In addn. it was exptl. confirmed that Mg1.0RE1.0Ni4H∼4 with La, Pr, and Nd transformed into Mg1.0RE1.0Ni4H∼6 with a C15b structure, while no formation of Mg1.0RE1.0Ni4H∼6 (RE = Sm and Gd) was obsd. at 40 MPa at 250 K. Theor. calcns. suggest that Mg1.0RE1.0Ni4H∼4 with Sm and Gd also transform to Mg1.0RE1.0Ni4H∼6 at higher pressures than those used in our expts. (264 MPa for Mg1.0Sm1.0Ni4 and 8.5 GPa for Mg1.0Gd1.0Ni4 at 253 K). The hydrogenation properties and crystal structure of the hydrides in Mg2-xRExNi4 are dependent on the alloy compn., i.e., the ratio of Mg to RE in the alloy phase, but independent of the choice of rare earth element.
    23. 23
      Sakaki, K.; Terashita, N.; Kim, H.; Proffen, T.; Majzoub, E. H.; Tsunokake, S.; Nakamura, Y.; Akiba, E. Crystal Structure and Local Structure of Mg2-xPrxNi4 (x = 0.6 and 1.0) Deuteride Using in Situ Neutron Total Scattering. Inorg. Chem. 2013, 52, 7010– 7019,  DOI: 10.1021/ic400528u
      23
      Crystal Structure and Local Structure of Mg2-xPrxNi4 (x = 0.6 and 1.0) Deuteride Using in Situ Neutron Total Scattering
      Sakaki, K.; Terashita, N.; Kim, H.; Proffen, T.; Majzoub, E. H.; Tsunokake, S.; Nakamura, Y.; Akiba, E.
      Inorganic Chemistry (2013), 52 (12), 7010-7019CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
      The authors studied crystal structure and local structure of Mg2-xPrxNi4 (x = 0.6 and 1.0) and their deuterides using in situ neutron total scattering and 1st-principles calcns. The total scattering data were analyzed using Rietveld refinement and pair distribution function anal. (PDF). The crystal structure of Mg2-xPrxNi4 before D absorption was C15b in space group F4-3m. Crystallog. data and at. coordinates are given. No difference between the crystal and local (PDF) structures was obsd. The crystal structure of Mg1.0Pr1.0Ni4D∼4 is orthorhombic in space group Pmn21, with three D occupation sites: PrNi3 and two types of bipyramidal Pr2MgNi2 that have a plane of symmetry composed of MgNi2. There is no significant difference between the crystal structure and the local structure of Mg1.0Pr1.0Ni4D∼4. However, the av. crystal structure of the Mg-rich Mg1.4Pr0.6Ni4D∼3.6 was C15b with two D occupation sites: PrNi3 and MgPrNi2 suggesting that the D occupation shifts away from the Pr2MgNi2 bipyramid. First-principles relaxed structures also showed the shift of the H occupation site toward the Pr atom of the bipyramid, when induced by Mg substitution for the opposing Pr, resulting in H occupation in the MgPrNi2 tetrahedral site. The PDF pattern of Mg1.4Pr0.6Ni4D∼3.6 cannot be refined <7.2 Å in at. distances using the C15b structure which was obtained from Rietveld refinement but can be done using an orthorhombic structure. Probably Mg1.4Pr0.6Ni4D∼3.6 was locally distorted to the orthorhombic.
    24. 24
      Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Riabov, A. B.; Zavaliy, I. Yu. Hydrogenation Properties and Crystal Structure of YMgT4 (T = Co, Ni, Cu) Compounds. J. Alloys Compd. 2014, 603, 7– 13,  DOI: 10.1016/j.jallcom.2014.03.030
      24
      Hydrogenation properties and crystal structure of YMgT4 (T = Co, Ni, Cu) compounds
      Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Riabov, A. B.; Zavaliy, I. Yu.
      Journal of Alloys and Compounds (2014), 603 (), 7-13CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      New two ternary YMgCo4 and YMgCu4 and one quaternary YMgCo2Ni2 compds. were synthesized by mech. alloying with further annealing. The hydrogenation capacity of YMgCo4 reaches 6.8 at.H/f.u. The Pressure-Compn.-Temp. studies of YMgCo4-H2 and YMgNi4-H2 systems revealed that introduction of magnesium, accompanied by shrinking of the unit cell, decreases the stability of hydrides comparing to binary YCo2 and YNi2 compds. The values of heat and entropy of the YMgCo4H6.8 hydride formation were calcd.: ΔH = -27.9 ± 0.8 kJ mol-1 H2 and ΔS = -93.4 ± 2.6 J mol-1 H2 K-1. The YMgCo2Ni2-H2 system shows intermediate thermodn. properties compared to the ternary hydrides (ΔH = -28.8 ± 0.2 kJ mol-1 H2 and ΔS = -117.6 ± 2.4 J mol-1 H2 K-1). The YMgCo4H6.8 and YMgCo2Ni2H4.9 hydrides keep the cubic structure of the parent compds. with a cell vol. expansion of 23 and 14.4% resp. The YMgCu4 compd. does not interact with hydrogen under normal conditions.
    25. 25
      Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Verbovytskyy, Yu. V; Zavaliy, I. Yu. Effect of Co Substitution on Hydrogenation and Magnetic Properties of NdMgNi4 Alloy. J. Alloys Compd. 2015, 639, 526– 532,  DOI: 10.1016/j.jallcom.2015.03.187
      25
      Effect of Co substitution on hydrogenation and magnetic properties of NdMgNi4 alloy
      Shtender, V. V.; Denys, R. V.; Paul-Boncour, V.; Verbovytskyy, Yu. V.; Zavaliy, I. Yu.
      Journal of Alloys and Compounds (2015), 639 (), 526-532CODEN: JALCEU; ISSN:0925-8388. (Elsevier B.V.)
      The influence of Co substitution on the structural and magnetic properties of NdMgNi4-xCox (x ≤ 3) alloys and their hydrides was investigated. The formation of NdMgCo4 compd. has not been obsd. The gas hydrogenation of these alloys resulted in the formation of NdMgNi4H4, NdMgNi3CoH4.8, NdMgNi2Co2H5.6 and NdMgNiCo3H6.2 hydrides. Transformation from cubic into orthorhombic structure upon hydrogenation was confirmed for NdMgNi4H4 hydride, whereas Co-contg. hydrides preserved the parent cubic structure. PC diagrams at 50° for NdMgNi4-xCox-H2 (x = 0, 2, 3) showed only one absorption/desorption plateau, which equil. pressure decrease as the cell vol. increase. The NdMgCu4 ternary compd. was synthesized, but it does not interact with hydrogen under normal conditions. Electrochem. investigations demonstrated that substitution of the nickel atoms by the cobalt ones in NdMgNi4 does not significantly influence on the max. discharge capacity (244-261 mA h/g) and all alloys are characterized by high cyclic stability. NdMgNi4 and its hydride display a Pauli paramagnet behavior. NdMgNi2Co2 displays a magnetic order below 50 K whereas its hydride shows a Pauli paramagnet behavior similar to that of NdMgNi4H4.
    26. 26
      Shtender, V. V.; Denys, R. V.; Zavaliy, I.Yu.; Zelinska, O. Ya.; Paul-Boncour, V.; Pavlyuk, V. V. Phase Equilibria in the Tb-Mg-Co System at 500 °C, Crystal Structure and Hydrogenation Properties of Selected Compounds. J. Solid State Chem. 2015, 232, 228– 235,  DOI: 10.1016/j.jssc.2015.09.031
      26
      Phase equilibria in the Tb-Mg-Co system at 500 °C, crystal structure and hydrogenation properties of selected compounds
      Shtender, V. V.; Denys, R. V.; Zavaliy, I. Yu.; Zelinska, O. Ya.; Paul-Boncour, V.; Pavlyuk, V. V.
      Journal of Solid State Chemistry (2015), 232 (), 228-235CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
      The isothermal section of the Tb-Mg-Co phase diagram at 500° was built on the basis of x-ray diffraction anal. of forty samples prepd. by powder metallurgy. The existence of two ternary compds. Tb4Mg3Co2 and Tb4MgCo was confirmed. The formation of two solid solns., Tb1-xMgxCo3 (0≤x≤0.4) and Tb1--xMgxCo2 (0≤x≤0.6), was found for the first time. Tb5Mg24 also dissolves a small amt. of Co. Other binary compds. do not dissolve the third component. The Tb4MgCo and TbMgCo4 compds. form hydrides (12.7 and 5.3 at.H/f.u. capacity, resp.) that retain the original structure of metallic matrixes. Upon thermal desorption the Tb4MgCoH12.7 hydride was stable up to 300° and disproportionated at higher temp. Two other hydrides, Tb4Mg3Co2H4 and Tb2MgCo9H12, are unstable in air and decomp. into the initial compds.
    27. 27
      Yang, T.; Yuan, Z.; Bu, W.; Jia, Z.; Qi, Y.; Zhang, Y. Effect of Elemental Substitution on the Structure and Hydrogen Storage Properties of LaMgNi4 Alloy. Mater. Des. 2016, 93, 46– 52,  DOI: 10.1016/j.matdes.2015.12.150
      27
      Effect of elemental substitution on the structure and hydrogen storage properties of LaMgNi4 alloy
      Yang, Tai; Yuan, Zeming; Bu, Wengang; Jia, Zhichao; Qi, Yan; Zhang, Yanghuan
      Materials & Design (2016), 93 (), 46-52CODEN: MADSD2; ISSN:0264-1275. (Elsevier Ltd.)
      Intermetallic compds. with the nominal formula LaMgNi3.6M0.4 (M = Ni, Co, Mn, Cu, Al) were prepd. through induction melting, and the structure and hydrogen storage properties of the resultant alloys were extensively investigated. Results showed that the alloys exhibit sizable hydrogen absorption capacity and that elemental substitution significantly influences their microstructure and hydrogen storage properties. The discharge capacities of the alloy electrodes decrease in the order Co > Ni > Al > Cu > Mn. Moreover, the electrochem. kinetics of the alloys depend on their microstructures and phase compns. Smaller grain size is helpful to improve the electrochem. kinetics. The gaseous hydrogen absorption capacities of the alloys are approx. 1.7 wt.% in the first hydrogenation process. Cracking caused by hydrogenation and dehydrogenation also significantly improves the hydrogen absorption kinetics of the alloy particles. The hydrogen storage capacities of the alloys rapidly decrease with increasing cycle no. This result is attributed to amorphisation of the LaMgNi4 phase during hydrogen absorption-desorption cycling (H2-induced amorphisation). Our findings provide new insights into the capacity degrdn. mechanism of La-Mg-Ni system hydrogen storage alloys that may improve their cycling stability.
    28. 28
      Shtender, V. V.; Paul-Boncour, V.; Denys, R. V.; Crivello, J.-C.; Zavaliy, I. Yu. TbMgNi4-xCox-(H,D)2 System. I: Synthesis, Hydrogenation Properties, and Crystal and Electronic Structures. J. Phys. Chem. C 2020, 124, 196– 204,  DOI: 10.1021/acs.jpcc.9b10252
      28
      TbMgNi4-xCox-(H,D)2 System. I: Synthesis, Hydrogenation Properties, and Crystal and Electronic Structures
      Shtender, Vitalii V.; Paul-Boncour, Valerie; Denys, Roman V.; Crivello, Jean-Claude; Zavaliy, Ihor Yu.
      Journal of Physical Chemistry C (2020), 124 (1), 196-204CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      A series of cubic TbMgNi4-xCox (x = 0-4) pseudo-binary compds. have been synthesized by either a solid-state reaction or mech. alloying with further annealing treatment. Their hydrogenation properties have been studied by pressure-compn.-temp. (PCT) measurements, showing the formation of α-, β-, and γ-hydrides. The Co for Ni substitution yields a lowering of the equil. pressure and an increase of the hydrogen capacity. An improvement of the kinetics of hydrogen absorption was obsd. with an increasing Co content. β-TbMgNi4-xCoxH∼4 (x = 0-3) hydrides show an orthorhombic distortion (Pmn21 space group), whereas the β-TbMgCo4H3.3 hydride crystallizes in a monoclinic structure (Pm space group) derived from the orthorhombic structure. Sensitivity of the formation of the β-TbMgCo4H3.3 hydride to temp. has been obsd. in PCT curves to exist below 50°C. γ-TbMgNi4-xCoxHy (x = 2-4, y > 5) hydrides preserve the parent cubic structure (F‾43m space group) with a hydrogen-induced vol. expansion of 17.9-22.3%. The deuterium for hydrogen substitution in the TbMgNiCo3-(H,D)2 system prevents fast desorption at room temp. and ambient pressure. The positions of deuterium atoms in the γ-TbMgCo4D6 deuteride were detd. by neutron powder diffraction. Two types of interstitial sites were found to be occupied: 87% of deuterium atoms (D1 site) are located inside Tb2MgCo2 octahedra and the remaining 13% (D2 site) are inside Co4 tetrahedra. The increase of the Co content allows the improvement of the thermodn. stability of TbMgNi4-xCox hydrides, as demonstrated by the lowering of the desorption plateau pressure, the increase of the desorption temp., and the increase of the enthalpy of formation vs. the Co content. This last exptl. result is confirmed by first-principles calcns. where electronic structures of intermetallic compds. and their cubic TbMgNi4-xCoxH6 hydrides are compared for x = 0, 2, and 4.
    29. 29
      Verbovytskyy, Y.; Oprysk, V.; Paul-Boncour, V.; Zavaliy, I.; Berezovets, V.; Lyutyy, P.; Kosarchyn, Y. Solid Gas and Electrochemical Hydrogenation of the Selected Alloys (R’,R”)2-xMgxNi4-yCoy (R’, R” = Pr, Nd; x = 0.8–1.2; y = 0–2). J. Alloys Compd. 2021, 876, 160155  DOI: 10.1016/j.jallcom.2021.160155
      There is no corresponding record for this reference.
    30. 30
      Sato, T.; Ikeda, K.; Honda, T.; Daemen, L. L.; Cheng, Y.; Otomo, T.; Sagayama, H.; Ramirez-Cuesta, A. J.; Takagi, S.; Kono, T. Effect of Co Substitution on Hydrogen Absorption and Desorption Reactions of YMgNi4-based Alloys. J. Phys. Chem. C 2022, 126, 16943– 16951,  DOI: 10.1021/acs.jpcc.2c03265
      There is no corresponding record for this reference.
    31. 31
      Sugimoto, H.; Fukai, Y. Solubility of Hydrogen in Metals under High Hydrogen Pressures: Thermodynamical Calculations. Acta Metall. Mater. 1992, 40, 2327– 2336,  DOI: 10.1016/0956-7151(92)90151-4
      31
      Solubility of hydrogen in metals under high hydrogen pressures: thermodynamical calculations
      Sugimoto, H.; Fukai, Y.
      Acta Metallurgica et Materialia (1992), 40 (9), 2327-36CODEN: AMATEB; ISSN:0956-7151.
      The soly. of H was calcd. up to high H pressures for ten metals having small solubilities under normal pressures. The equation of state of H was calcd. by the procedure of H. Hemmes et al. (1986), and the values obtained for the molar volume, enthalpy, Gibbs free energy, and entropy are tabulated in the range 0.1-100 GPa and 400-2000 K. For soly. calcns., the chem. potential of H in solid soln. was detd. The solubilities obtained for fcc. metals Al, γ-Fe, Ni, Cu, Ag, Pt, Au and bcc. metals Cr, α-Fe, Mo, W are shown in the form of Arrhenius relations with pressure as a parameter. Strong enhancements of the soly. over Sieverts law were found at high H pressures ≥1 GPa.
    32. 32
      Saitoh, H.; Sato, T.; Tanikami, M.; Ikeda, K.; Machida, A.; Watanuki, T.; Taguchi, T.; Yamamoto, S.; Yamaki, T.; Takagi, S. Hydrogen Storage by Earth-Abundant Metals, Synthesis and Characterization of Al3FeH3.9. Mater. Des. 2021, 208, 109953  DOI: 10.1016/j.matdes.2021.109953
      There is no corresponding record for this reference.
    33. 33
      Fischer, P.; Frey, G.; Koch, M.; Könnecke, M.; Pomjakushin, V.; Schefer, J.; Thut, R.; Schlumpf, N.; Bürge, R.; Greuter, U. High-Resolution Powder Diffractometer HRPT for Thermal Neutrons at SINQ. Physica B 2000, 146–147, 276– 278,  DOI: 10.1016/S0921-4526(99)01399-X
      There is no corresponding record for this reference.
    34. 34
      Werner, P.-E.; Eriksson, L.; Westdahl, M. TREOR, A Semi-Exhaustive Trial–and–Error Powder Indexing Program for All Symmetries. J. Appl. Crystallogr. 1985, 18, 367– 370,  DOI: 10.1107/S0021889885010512
      34
      TREOR, a semi-exhaustive trial-and-error powder indexing program for all symmetries
      Werner, P. E.; Eriksson, L.; Westdahl, M.
      Journal of Applied Crystallography (1985), 18 (5), 367-70CODEN: JACGAR; ISSN:0021-8898.
      An indexing program, TREOR, mainly based on trial-and-error methods, is described. The program contains sep. routines for cubic, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic symmetries. Ten years usage was analyzed to improve the original program. For monoclinic indexing, a specific short-axis test was developed. The over-all success rate of the program is >90%, and considerably more for orthorhombic and higher symmetries.
    35. 35
      Werner, P.-E. A Fortran Program for Least-Squares Refinement of Crystal-Structure Cell Dimensions. Ark. Kemi 1969, 31, 513– 516
      35
      Fortran program for least-squares refinement of crystal-structure cell dimensions
      Werner, Per Erik
      Arkiv foer Kemi (1969), 31 (43), 513-16CODEN: ARKEAD; ISSN:0365-6128.
      A FORTRAN computer program was constructed for indexing powder patterns and least-squares refinement of crystal structure cell dimensions.
    36. 36
      Toby, B. H. EXPGUI, A Graphical User Interface for GSAS. J. Appl. Crystallogr. 2001, 34, 210– 213,  DOI: 10.1107/S0021889801002242
      36
      EXPGUI, a graphical user interface for GSAS
      Toby, Brian H.
      Journal of Applied Crystallography (2001), 34 (2), 210-213CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
      A description and justification of the EXPGUI program is presented. This program implements a graphical user interface and shell for the GSAS (Generalized Structure and Anal. Software) single-crystal and Rietveld package. Use of the Tcl/Tk scripting language allows EXPGUI to be platform independent. Also included is a synopsis of how the program is implemented.
    37. 37
      Nylén, J.; Sato, T.; Soignard, E.; Yarger, J. L.; Stoyanov, E.; Häussermann, U. Thermal Decomposition of Ammonia Borane at High Pressures. J. Chem. Phys. 2009, 131, 104506,  DOI: 10.1063/1.3230973
      37
      Thermal decomposition of ammonia borane at high pressures
      Nylen, Johanna; Sato, Toyoto; Soignard, Emmanuel; Yarger, Jeffery L.; Stoyanov, Emil; Haussermann, Ulrich
      Journal of Chemical Physics (2009), 131 (10), 104506/1-104506/7CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      The effects of high pressure (up to 9 GPa) on the thermal decompn. of ammonia borane, BH3NH3, were studied in situ by Raman spectroscopy in a diamond anvil cell. In contrast with the three-step decompn. at ambient pressure, thermolysis under pressure releases almost the entire hydrogen content of the mol. in two distinct steps. The residual of the first decompn. is polymeric aminoborane, (BH2NH2)x, which is also obsd. at ambient pressure. The residual after the second decompn. is unique to high pressure. Presumably it corresponds to a precursor to hexagonal BN where macromol. fragments of planar hexagon layers formed by B and N atoms are terminated by H atoms. Increasing pressure increases the temp. of both decompn. steps. Due to the increased first decompn. temp. it becomes possible to observe a new high pressure, high temp. phase of BH3NH3 which may represent melting. (c) 2009 American Institute of Physics.
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      Nylén, J.; Eriksson, L.; Benson, D.; Häussermann, U. Characterization of a High pressure, High Temperature Modification of Ammonia Borane (BH3NH3). J. Chem. Phys. 2013, 139, 054507  DOI: 10.1063/1.4817188
      38
      Characterization of a high pressure, high temperature modification of ammonia borane (BH3NH3)
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      Journal of Chemical Physics (2013), 139 (5), 054507/1-054507/7CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      At elevated pressures (above 1.5 GPa) dihydrogen bonded NH3 borane, BH3NH3, undergoes a solid-solid phase transition with increasing temp. The high pressure, high temp. (HPHT) phase precedes decompn. and evolves from the known high pressure, low temp. form with space group symmetry Cmc21 (Z = 4). Structural changes of BH3NH3 with temp. were studied at ∼6 GPa in a diamond anvil cell by synchrotron powder diffraction. At this pressure the Cmc21 phase transforms into the HPHT phase at ∼140°. The crystal system, unit cell, and B and N atom position parameters of the HPHT phase were extd. from diffraction data, and a H ordered model with space group symmetry Pnma (Z = 4) subsequently established from d. functional calcns. However, there is strong exptl. evidence that HPHT-BH3NH3 is a H disordered rotator phase. A reverse transition to the Cmc21 phase is not obsd. When releasing pressure at room temp. to <1.5 GPa the ambient pressure (H disordered) I4mm phase of BH3NH3 was obtained. (c) 2013 American Institute of Physics.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.4c06759.

    • X-ray diffraction patterns of the starting materials YCo2 and MgNi2; Rietveld refinement fits of synchrotron radiation X-ray diffraction and neutron diffraction; and crystallographic parameters (PDF)


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