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 α- to pseudo-tetragonal β-ZrV2O7 that displays an orthorhombic 2 × 3 × 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 (B0) for TiP2O7, ZrP2O7, α-ZrV2O7 and β-ZrV2O7 were estimated to be 42  (3), 39  (1), 17.0  (7) and 20.8  (10)  GPa, respectively.

Nyckelord

phase transformations • high-pressure diffraction • titanium pyrophosphate • zirconium pyrophosphate • zirconium pyrovanadate • negative thermal expansion • pressure amorphization.

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