Abstract
Local symmetry breaking in PbxSr1−xTiO3 (PST) solid solutions was revealed by Raman spectroscopy below and above the ferroelectric phase-transition temperature. In the paraelectric phase, local symmetry breaking associated with the polar clusters localized mostly at grain boundaries in ceramic samples leads to the activation of the polar modes far above the dielectric maximum. This effect was found remarkably enhanced in the PST:MgO composites due to the compositional inhomogeneity of the grain boundaries and the intergrain stresses in the composite. In the ferroelectric phase, the degeneracy of the E(TO1) soft mode was lifted due to translational symmetry breaking in the solid solutions with x=0.2 and 0.3, where the substitution of Sr by Pb replaces partially the ionic bonding between the A cations and the oxygens by a stronger covalent bonding.
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