Pressure-induced phase transition of Lu₂Ti₂O₇ and Lu_1.5Ce_0.5Ti₂O_7+x pyrochlores

This study utilizes both experimental and computational approaches to investigate the performance of Lu2Ti2O7 (LTO) and Lu1.5Ce0.5Ti2O7+x (LCTO) pyrochlores under high pressure. The structural changes of LTO and LCTO pyrochlores were characterized using in-situ synchrotron x-ray diffraction (SXRD) and in-situ Raman spectroscopy at pressures up to 44.6 GPa. The kinks in P-a and P-V curves at around 5 GPa are mainly attributed to the interaction between the pressure medium and the isostructural changes. The onset pressures for transitioning from the cubic pyrochlore phase (Fd-3 m) to the monoclinic phase (P2(1)) are observed at 32.5 GPa and 38.1 GPa, respectively. It is important to note that at the highest measured pressures, the phase transition remains incomplete. This partial transition is likely the result of oriented disorder among cations and anions under high pressure. In addition, introducing Ce as a dopant significantly enhances structural stability. This can be explained by the larger ionic radius of Ce, which hinders the disordering process.