Pressure-induced order-disorder transition in Gd1.5Ce0.5Ti2O7 pyrochlore

Abstract

An experimental study on ordered pyrochlore structured Gd_1.5Ce_0.5Ti₂O₇ $\left(Fd\overline{3}m\right)$ was carried out up to 45 GPa by synchrotron radiation X-ray diffraction and Raman spectroscopy. Experimental results show that Gd_1.5Ce_0.5Ti₂O₇ transfers to a disordered cotunnite-like phase (Pnma Z = 4) at approximately 42 GPa. Compared with the end member Gd₂Ti₂O₇, the substitution of Ce³⁺ for Gd³⁺ increases the transition pressure and the high-pressure stability of the pyrochlore phase. This pressure-induced structure transition is mainly controlled by cationic order-disorder modification, and the cationic radius ratio r _A/r _B may also be effective for predicting the pyrochlore oxides' high-pressure stability. Two isostructural transitions are observed at 6.5 GPa and 13 GPa, and the unit-cell volume of Gd_1.5Ce_0.5Ti₂O₇ as a function of pressure demonstrates its compression behaviour is rather complex.

Keywords: high pressure; order–disorder phase transition; pyrochlore.