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.

Pressure-induced phase transition of Lu2Ti2O7 and Lu1.5Ce0.5Ti2O7+x pyrochlores

“…However, the transition near 9 GPa was observed with both pressure medium, which is controversy to the conclusion made by Zhang. The compressibility changes at the pressures below 10 GPa were also reported by Niu et al [20], the pressure media used in this work are silicon oil and gas argon, so they assigned the abrupt changes in compressibility to the isostructural changes in pyrochlores. As discussed above, the 'kinks' are commonly reported, but the reason of this abnormal changes is still confusing.…”

“…Similar peak shifting and intensity decreasing can also be seen in the in-situ SXRD patterns. These changes can be interpreted by the shortening of bond lengths and the decrease of the ordering within the pyrochlore as pressure increases [18,20]. It is worth noting that the intensity of all Raman modes for LTO increases when the pressure increases from 0 GPa to 4.8 GPa.…”

“…Prior to the break point, both the lattice parameter a and the cell volume V decrease sharply with increasing pressure. However, the rates of decrease slow down after around 5 GPa, we summarized the pressure media used in high pressure studies on pyrochlore, different media such as silicone oil, water, methanol and ethanol mixtures, argon, helium and neon were used as pressure transfer media [11,13,18,20]. Ar, methanol/ethanol with or without water were used as pressure media in Zhang's study [18].…”

High‐Valence Oxides for High Performance Oxygen Evolution Electrocatalysis

“…Reproduced under the terms of the Creative Commons Attribution License. [ 118 ] Copyright 2019, The Authors, published by the Royal Society. b) CVs and corresponding TOFs (inset) of porous Y 2 [Ru 1.6 Y 0.4 ]O 7− δ , Y 2 Ru 2 O 7− δ and RuO 2 electrocatalysts.…”