High-pressure Raman and optical absorption studies on lead pyroniobate (Pb₂Nb₂O₇) and pressure-induced phase transitions

Abstract

High-pressure Raman scattering and optical absorption studies have been carried out on lead pyroniobate up to 33 GPa, using a gasketed diamond anvil cell. The Raman study reveals the occurrence of two, possibly three, pressure-induced phase changes; a rather subtle change is indicated near 4.5 GPa. The transition near 13 GPa is attributed to a structural transition from the rhombohedral to the cubic pyrochlore structure. The third phase change occurs near 20 GPa. From the broad Raman feature that is observed at about 800 cm^-1, it is concluded that the system turns amorphous at pressures above 20 GPa. The amorphous phase recrystallizes to the original rhombohedral phase, on release of pressure.