Pressure-induced phase transition of La(2)Zr(2)O(7) and La(0.5)Gd(1.5)Zr(2)O(7) pyrochlore

In situ high-pressure experiments on La(2)Zr(2)O(7) and La(0.5)Gd(1.5)Zr(2)O(7) have been carried out at up to approximately 40 GPa using synchrotron X-ray diffraction and Raman spectroscopy combined with a diamond anvil cell technique. Both La(2)Zr(2)O(7) and La(0.5)Gd(1.5)Zr(2)O(7) undergo a phase transition from a pyrochlore phase (Fd3̄m) into a cotunnite-like phase (Pnma) at 22.7 and 23.3 GPa, respectively. This type of phase transition is mainly controlled through the order-disorder occupancy of cations, and Gd(3+) substitution of La(3+) reduces the stability of zirconate pyrochlore. However, abnormal changes to the unit-cell volumes and vibrational modes observed at 5.5 GPa in La(2)Zr(2)O(7) and 6.5 GPa in La(0.5)Gd(1.5)Zr(2)O(7) are attributed to an anion disorder in the pyrochlore.