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, BaV₂O₆·H₂O, 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 BaV₂O₆·H₂O 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 BaV₂O₆·H₂O 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 BaV₂O₆·H₂O is one of the most compressible vanadates with a bulk modulus of 33.0(5) GPa.