Successive pressure-induced structural transitions in relaxor Pb(In$_{1/2}$Nb$_{1/2})$O$_{3}$

We employed Raman scattering and x-ray diffraction to investigate the behavior of disordered Pb(In$_{1/2}$Nb$_{1/2})$O$_{3}$ (PIN) under pressure up to 50 GPa at 300 K. The sharp peak centered at 370 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. In most Pb-based relaxors, in contrast to PIN, the 50 cm$^{-1}$ peak shows a slight hardening with pressure and no splitting is observed. The pressure evolution of the diffraction patterns for PIN shows obvious splittings above 16 GPa, particularly for the pseudo-cubic [110], [111] and [220] diffraction peaks, indicative of a symmetry-lowering transition. Our results demonstrate that PIN undergoes successive structural phase transitions. The transition at 6 GPa is similar to that observed in other Pb-based relaxors and related to the octahedra tilting; the transition at 16 GPa could be a rhombohedral to orthorhombic transition, and the transition at 38 GPa is assigned to an orthorhombic to a monoclinic transition.