High-pressure properties of TiP2O7, ZrP2O7 and ZrV2O7

High-pressure synchrotron X-ray powder diffraction studies of TiP2O7, ZrP2O7 and ZrV2O7 have been performed. The ZrV2O7 structure undergoes a reversible transition at 1.38-1.58 GPa from cubic alpha- to pseudo-tetragonal beta -ZrV2O7 that displays an orthorhombic 2 x 3 x 3 supercell. At pressures above 4 GPa, ZrV2O7 becomes irreversibly X-ray amorphous. No such transformations are observed for TiP2O7 and 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 (B-0) for TiP2O7, ZrP2O7, alpha -ZrV2O7 and beta -ZrV2O7 were estimated to be 42 (3), 39 (1), 17.0 (7) and 20.8 (10) GPa, respectively.