The role of π-blocking hydride ligands in a pressure-induced insulator-to-metal phase transition in SrVO2H

Transition-metal oxyhydrides are of considerable current interest due to the unique features of the hydride anion, most notably the absence of valence p orbitals. This feature distinguishes hydrides from all other anions, and gives rise to unprecedented properties in this new class of materials. Here we show via a high-pressure study of anion-ordered strontium vanadium oxyhydride SrVO2H that H- is extraordinarily compressible, and that pressure drives a transition from a Mott insulator to a metal at similar to 50 GPa. Density functional theory suggests that the band gap in the insulating state is reduced by pressure as a result of increased dispersion in the ab-plane due to enhanced V-d pi-O-p pi-V-d pi overlap. Remarkably, dispersion along c is limited by the orthogonal V-d pi-H-1s-V-d pi arrangement despite the greater c-axis compressibility, suggesting that the hydride anions act as pi-blockers. The wider family of oxyhydrides may therefore give access to dimensionally reduced structures with novel electronic properties.