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Pressure-induced order-disorder transition in Gd1.5Ce0.5Ti2O7 pyrochlore
Jingjing Niu1,2,3, Xiang Wu4, Haibin Zhang3
1Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, People's Republic of China.
Abstract:
An experimental study on ordered pyrochlore structured Gd1.5Ce0.5Ti2O7 was carried out up to 45 GPa by synchrotron radiation X-ray diffraction and Raman spectroscopy. Experimental results show that Gd1.5Ce0.5Ti2O7 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 Gd1.5Ce0.5Ti2O7 as a function of pressure demonstrates its compression behaviour is rather complex.
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