High-pressure properties of TiP2O7, ZrP2O7and ZrV2O7

Abstract

High-pressure synchrotron X-ray powder diffraction studies of TiP2O7, ZrP2O7and ZrV2O7have been performed. The ZrV2O7structure undergoes a reversible transition at 1.38–1.58 GPa from cubic α- to pseudo-tetragonal β-ZrV2O7that displays an orthorhombic 2 × 3 × 3 supercell. At pressures above 4 GPa, ZrV2O7becomes irreversibly X-ray amorphous. No such transformations are observed for TiP2O7and ZrP2O7, which compress smoothly up to the highest investigated pressures (40.3 and 20.5 GPa, respectively). These differences in high-pressure properties are discussed in terms of the negative thermal expansion of ZrV2O7. The bulk moduli at ambient pressure (B0) for TiP2O7, ZrP2O7, α-ZrV2O7and β-ZrV2O7were estimated to be 42 (3), 39 (1), 17.0 (7) and 20.8 (10) GPa, respectively.