Structural changes and pressure-induced amorphization in rare earth titanates RE2Ti2O7 (RE: Gd, Sm) with pyrochlore structure

Structural changes of pyrochlore titanates, Sm2Ti2O7 and Gd2Ti2O7, at high pressures were studied by in situ Raman scattering and X-ray diffraction (XRD) methods. The Raman experiments revealed that RE2Ti2O7 lost pyrochlore structural character at pressures of 40 GPa and 38 GPa for RE = Sm and Gd, respectively. However, XRD results found that they were only partially amorphized up to 51 GPa. The crystalline phase at high pressure is a distorted pyrochlore - the anions have lost long-range order while the rare earth ions still keep some ordering. Both of the pyrochlores became completely amorphous after releasing pressure from 51 GPa.