High-Pressure Synthesis of Transition-Metal Oxyhydrides with Double-Perovskite Structures.

We report on the high-pressure synthesis, crystal structure, and magnetic properties of four novel transition-metal oxyhydrides─Ba 2 NaVO 3 H 3 , Ba 2 NaVO 2.4 H 3.6 , Ba 2 NaCrO 2.2 H 3.8 , and Ba 2 NaTiO 3 H 3 ─crystallizing in the double-perovskite structure. Notably, they have a higher hydride content in their anion sites (50%-63%) than known oxyhydrides with perovskite structures do (≤33%). Vanadium and chromium oxyhydrides exhibited Curie-Weiss magnetic susceptibilities with no magnetic ordering down to 2 K, which may be due to geometrical frustration in their face-centered lattices and weak magnetic interactions. Density functional theory calculations revealed that the transition metal-hydride bonding nature of the prepared oxyhydrides is more covalent than that observed for known perovskite oxyhydrides, as evidenced by the shorter bond lengths of the former. Remarkably, our double-perovskite oxyhydrides with a high hydride content may possess a bonding character intermediate between those of known oxyhydrides and hydrides.