Successive Pressure-Induced Structural Transitions in Relaxor Lead Indium Niobate

We employed Raman scattering and x-ray diffraction to investigate the behavior of disordered perovskite-type Pb(In1/2Nb1/2)O-3 (PIN) under high pressure up to 50 GPa at 300 K. The sharp peak centered at 380 cm(-1) increases its intensity with pressure. Two Raman peaks around 550 cm(-1) merge at 16 GPa and their linewidths increase with pressure. The structural phase transition is associated with a splitting of the 50 cm(-1) peak above 16 GPa. The pressure evolution of the diffraction patterns for PIN shows obvious splitting above 16 GPa and 33 GPa, particularly for the pseudo-cubic (110), (200), and (211) diffraction peaks, indicative of a symmetry-lowering transition. Our results demonstrate that PIN undergoes successive structural phase transitions: a pseudcubic to orthorhombic at 0.5 GPa; a transition from orthorhombic to orthorhombic at 16 GPa due to enhanced octahedra tilting and change in linear compressibility; the transition at 33 GPa is plausibly a transition to a monoclinic phase.