Structural distortions and phase transformations in Sm2Zr2O7 pyrochlore at high pressures

The structural characteristics of Sm2Zr2O7, an ordered pyrochlore, were studied by angle-dispersive X-ray diffraction (XRD) and Raman scattering methods with increasing pressure. A structural distortion was observed at low pressures; but the distortion disappeared at pressures above 13.5 GPa. Above 18 GPa, the pyrochlore structure is unstable and a pressure-induced phase transition occurred. The high-pressure phase is a distorted fluorite structure in which the cations and anion vacancies are disordered. The disordered structure is accompanied by the formation of partially amorphous domains. With the release of pressure, the high-pressure phase partially transforms to the amorphous state.