Structural transitions in Pb(In1/2Nb1/2)O-3 under pressure

Room-temperature Raman scattering and x-ray diffraction measurements together with first-principles calculations were employed to investigate the behavior of disordered Pb(In1/2Nb1/2)O-3 (PIN) under pressure up to 50 GPa. Raman spectra show broad bands but a peak near the 380 cm(-1) increases its intensity with pressure. The linewidth of the band at 550 cm(-1) also increases with pressure, while two of the Raman peaks merge above 6 GPa. Above 16 GPa, we observe additional splitting of the band at 50 cm(-1). The pressure evolution of the diffraction patterns for PIN shows obvious Bragg peaks splitting above 16 GPa; consistent with a symmetry lowering transition. The transition at 0.5 GPa is identified as a pseudo-cubic to orthorhombic (Pbam) structural change whereas the transition at 16 GPa is isostructure and associated with changes in linear compressibility and octahedral titling, and the transition at 30 GPa is associated to an orthorhombic to monoclinic change. First-principles calculations indicate that the Pbam structure is ground state with antiferrodisdortion consistent with experiment.