High-pressure study of barium metavanadate monohydrate

This study presents a single-crystal X-ray diffraction investigation of the high-pressure behavior of barium metavanadate monohydrate, BaV2O6H2O, up to 7.1 GPa. These measurements were combined with high-pressure optical absorption measurements performed up to 10.1 GPa and with density-functional theory calculations. The X-ray diffraction analysis indicates that BaV2O6H2O adopts an orthorhombic structure described by the space group P212121 at ambient pressure. This structure maintains stability up to 8 GPa, in contrast to anhydrous BaV2O6 which undergoes a phase transition at 4 GPa. Throughout the pressure range examined, the compression of the crystal is highly anisotropic with the b-axis exhibiting nearly zero linear compressibility. Additionally, our optical absorption measurements reveal that BaV2O6H2O exhibits an indirect band gap that decreases from 4.62(5) eV at 0.03 GPa to 4.48(5) eV at 10.1 GPa. Density-functional theory calculations give similar results to the experiments and support that the decrease of the band-gap energy with pressure is caused by the enhancement of the hybridization between O 2p and V 3d states. We have also calculated the elastic constant. According to experiments and calculations BaV2O6H2O is one of the most compressible vanadates with a bulk modulus of 33.0(5) GPa.