| 研究実績の概要 |
After our recent discover of LnHO with Ln = Sm, Gd, Tb, Dy, Ho, and Er, the hydride (H-) conductivity has been measured. It is found that, despite its “stoichiometric” composition, the anion-ordered phase (Ln = La, Nd) exhibits hydride conductivity (e.g., 2.3 × 10-S S cm-1 for NdHO at 300 °C), while the anion-disordered one (Ln = Gd, Er) is an ionic insulator. The systematic structural analysis combined with computational calculations has revealed the indirect interstitial mechanism, where H- anions migrate between the tetrahedral and octahedral sites through a triangular Ln3 bottleneck expanded by the anion order, with a critical bottleneck radius of 1.18 A. Besides that, another series of materials have been developed by exploiting hydride anions (H-) properties to construct a soft anion-sublattice together with chalcogens, in a previously unexplored antiperovskites series. Despite a large size variation for each Ch and M, the M3HCh antiperovskites (M = Li, Na; Ch = Chalcogen) adopt the ideal cubic structure (except orthorhombic Na3HS). Unlike traditional perovskites, such robustness of cubic phase originates from the extreme size-flexibility/polarizability of H-anions. Theoretical and experimental studies reveal low migration barriers for Li+/Na+ transport and high ionic conductivity, possibly promoted by a soft phonon mode associated with the rotational motion of HM6 octahedra in this soft cubic lattice. Hydride-based antiperovskites are thus offering a new direction for material design to explore.
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