Pressure-induced order–disorder transitions in pyrochlore RE2Ti2O7 (RE = Y, Gd)

Structure evolution of pyrochlore titanates Y2Ti2O7 and Gd2Ti2O7 at high pressure was investigated with Raman and X-ray diffraction methods. Pressure-induced order–disorder transitions are found in titanate pyrochlores. The cations and anions in Y2Ti2O7 began to be disordered at pressures above 50 GPa and the structure changes from pyrochlore (Fd-3m) to defect fluorite structure (Fm-3m) A4O7. This transition is not stable in Gd2Ti2O7, and amorphization proceeds at pressure above 32 GPa.