Structure and electrical properties of a single-crystal layered strontium manganese vanadate as a function of pressure*

We investigate the structural and electrical properties of a strontium manganese vanadate layered material, SrMn₂(VO₄)₂(OH)(H₂O), as a function of hydrostatic pressure. The material crystalizes in the space group C2/m. Variable temperature conductivity measurements, performed on single crystals, indicate semiconducting behavior, supported by DFT calculations. The manganese vanadate layers, consisting of chains of edge sharing MnO₆ octahedra bridged by corner-sharing VO₄ tetrahedra, are connected in the third dimension by octahedral Sr ions. Single-crystal x-ray diffraction under pressure up to 4 GPa indicates a reversible compression of the interlayer distance. The electrical conductivity of a single crystal as a function of pressure decreases at moderate pressures; beyond 0.4 GPa, the material is highly insulating. Interestingly, this change is not reversible. The same irreversible change in conductivity is also observed for the Ca and Ba analogs. Probing structural details at the lower pressure range by Raman spectroscopy, we observe a softening mode around 0.8 GPa related to the Mn octahedra.