High pressure synthesis of novel Li-TM hydrides (TM = Nb, Ta)

High-pressure synthesis has been widely used for exploration of novel materials. In this study, new Li-based hydrides in Li-Nb and Li-Ta systems have been successfully synthesized under GPa-order by using a cubic-anvil-type apparatus. And crystal structures, thermal stabilities of novel hydrides were investigated. For Li-Nb-H system, novel hydride with primitive hexagonal structure was synthesized at 973 K under 5 GPa. Its lattice parameter was a = 0.56250(5) nm, c = 0.57416(4) nm. A structural model of the hydride was CaCu5-type structure (P6/mmm, No. 191). For Li-Ta system, novel hydride with C-face centered monoclinic structure was obtained at 973 K under 5 GPa. Its lattice parameter was a = 0.7918(5) nm, b = 0.8012(4) nm, c = 1.030(7) nm, β = 111.27 (6)°. These novel hydrides in Li-Nb and Li-Ta systems were decomposed at 510 K and 573 K, respectively, and these values were about 400 K lower than that of LiH (>953 K).