β-Phase Yb5Sb3Hx: Magnetic and Thermoelectric Properties Traversing from an Electride to a Semiconductor

An electride is a compound that contains a localized electron in an empty crystallographic site. This class of materials has a wide range of applications, including superconductivity, batteries, photonics, and catalysis. Both polymorphs of Yb5Sb3 (the orthorhombic Ca5Sb3F structure type (β phase) and hexagonal Mn5Si3 structure type (α phase)) are known to be electrides with electrons localized in 0D tetrahedral cavities and 1D octahedral chains, respectively. In the case of the orthorhombic β phase, an interstitial H can occupy the 0D tetrahedral cavity, accepting the anionic electron that would otherwise occupy the site, providing the formula of Yb5Sb3Hx. DFT computations show that the hexagonal structure is energetically favored without hydrogen and that the orthorhombic structure is more stable with hydrogen. Polycrystalline samples of orthorhombic β phase Yb5Sb3Hx (x = 0.25, 0.50, 0.75, 1.0) were synthesized, and both PXRD lattice parameters and 1H MAS NMR were used to characterize H composition. Magnetic and electronic transport properties were measured to characterize the transition from the electride (semimetal) to the semiconductor. Magnetic susceptibility measurements indicate a magnetic moment that can be interpreted as resulting from either the localized antiferromagnetically coupled electride or the presence of a small amount of Yb3+. At lower H content (x = 0.25, 0.50), a low charge carrier mobility consistent with localized electride states is observed. In contrast, at higher H content (x = 0.75, 1.0), a high charge carrier mobility is consistent with free electrons in a semiconductor. All compositions show low thermal conductivity, suggesting a potentially promising thermoelectric material if charge carrier concentration can be fine-tuned. This work provides an understanding of the structure and electronic properties of the electride and semiconductor, Yb5Sb3Hx, and opens the door to the interstitial design of electrides to tune thermoelectric properties.


1.0
The 1 H MAS NMR spectrum from an empty rotor has a broad signal and a narrow signal with spinning sidebands.Using Bruker's Topspin software, and an NMR spectral fitting software DMFIT (https://nmr.cemhti.cnrs-orleans.fr/dmfit/)we simulated the experimental spectrum of the background signal with two components.The fitting parameters are given in Table S5.
The spectrum can be fitted with a relatively narrow signal with the isotropic chemical shift at 6.63 ppm with spinning sidebands, and a broad signal centered at 13.5 ppm.The sum of the two simulated components is in good agreement with the experimental data, with 95.6% overlapping, leaving the uncertainty to less than 5%.The narrow signal with spinning sidebands can be assigned to the 1 H signals from the Vespel cap and bottom-tip.The broad signal can be assigned to the hydrogen atoms present in the stator block.The 1 H MAS NMR spectra of Yb5Sb3Hx (x = 0.25, 0.5, 0.75, and 1.0) showed extra signal intensities on top of the instrument background.The deconvolution results are displayed in Table S5.

Figure S5 .
Figure S5.Magnetic susceptibility and analysis of YbH2 powder Figure S6.Experimental electrical resistivity data

Figure S1 .
Figure S1.Portion of typical Rietveld refinements of Yb5Sb3Hx (x = 0.25, 0.50, 0.75, 1.0).The observed data are shown in black, calculated pattern in red, and difference curve is in gray.

a
Figure S2.A portion of a typical Rietveld refinement of the Yb4Sb3 precursor.

Figure S5 .Figure S6 .
Figure S5.Magnetization measurements (at 300 K) for YbH2 precursor.Calculations of the amount of Fe impurity that would contribute to the ferromagnetic component of the Yb5Sb3Hx samples are shown.

Figure S8 .
Figure S8.Experimental carrier concentration data of Yb5Sb3Hx with x = 0.25, 0.50, 0.75 and 1.0 from the first heating cycle.

Figure S9 .
Figure S9.Experimental mobility data of Yb5Sb3Hx with x = 0.25, 0.50, 0.75 and 1.0 from the first heating cycle.

Figure S10 .
Figure S10.Experimental thermal conductivity data of Yb5Sb3Hx with x = 0.25, 0.50, 0.75 and 1.0 from the first heating cycle.

Table of ContentsTable S1 .
Atomic Coordinates of Yb5Sb3Hx after Structure Relaxation Calculations

Table S2 .
Statistics for Rietveld refinements of Yb5Sb3Hx PXRD data

Table S3 .
Statistics for Rietveld refinements of Yb4Sb3 PXRD data

Table S4 .
EDS data

Table S5 .
1 H MAS NMR spectral fitting parameters

Table S1 .
Atomic Coordinates of Yb5Sb3Hx after Structure Relaxation Calculations

Table S2 .
Selected Rietveld Refinement Statistics for Yb5Sb3Hx a

Table S4 .
EDS data for Yb5Sb3Hx (H cannot be detected).

Table S5 .
1 H MAS NMR spectral fitting parameters Isotropic chemical shift d(CSA): Chemical Shift Anisotropy, the unit is in ppm with a Larmer frequency of 500.03MHz h(CSA): Asymmetry parameter LB: Full width at half height a after background subtraction and sample weight normalization