Pressure-induced order–disorder transition in Gd _1.5 Ce _0.5 Ti ₂ O ₇ pyrochlore

Abstract

An experimental study on ordered pyrochlore structured Gd 1.5 Ce 0.5 Ti 2 O 7 ( F d 3 ¯ m ) was carried out up to 45 GPa by synchrotron radiation X-ray diffraction and Raman spectroscopy. Experimental results show that Gd 1.5 Ce 0.5 Ti 2 O 7 transfers to a disordered cotunnite-like phase ( Pnma Z = 4) at approximately 42 GPa. Compared with the end member Gd 2 Ti 2 O 7 , the substitution of Ce 3+ for Gd 3+ 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 1.5 Ce 0.5 Ti 2 O 7 as a function of pressure demonstrates its compression behaviour is rather complex.