Ferroic nanoclusters in relaxors: the effect of oxygen vacancies

High pressure Raman spectroscopic study on the relaxor ferroelectric PbSc(0.5)Nb(0.5)O(3)

The pressure evolution of the local structure and dynamics of polar nanoregions in PbSc(0.5)Nb(0.5)O(3) relaxor ferroelectric is analysed by Raman spectroscopy. The pressure dependence of phonon modes up to 10 GPa reveals three characteristic pressures related to changes in the local structure: near 2 GPa, at which ferroic ordering in the Pb system occurs; near 4 GPa, at which significant structural transformations, involving decoupling of Pb and B-cations in polar nanoclusters and suppression of the B-cation off-centring take place; and near 6 GPa, at which the system reaches a saturation state. The structural transformations observed in PbSc(0.5)Nb(0.5)O(3) are compared to those in PbSc(0.5)Ta(0.5)O(3) and other Pb-based perovskite-type relaxor ferroelectrics.

Pressure-induced phase transition in PbSc0.5Ta0.5O3 as a model Pb-based perovksite-type relaxor ferroelectric

We report pressure-induced structural changes in PbSc(0.5)Ta(0.5)O3 studied by single-crystal x-ray diffraction and Raman scattering. The appearance of a soft mode, a change in the volume compressibility, broadening of the diffraction peaks, and suppression of the x-ray diffuse scattering show that a phase transition occurs near pc approximately 1.9 GPa. The critical pressure is associated with a decoupling of the displacements of the B site and Pb cations in the existing polar nanoregions, leading to the suppression of B-cation off-center shifts and enhancement of the ferroic distortion in the Pb-O system.