Ferroic clustering and phonon anomalies in Pb-based perovskite-type relaxors

Abstract

The phonon anomalies and their relationship to the structural inhomogeneitiesin Pb-based relaxors are studied on the basis of stoichiometricPbSc0.5Ta0.5O3 andPbSc0.5Nb0.5O3 and Nb-, Sn- andBa-containing PbSc0.5Ta0.5O3. The ferroic clustering and the development of the ferroelectric state canbe followed by analysing quantitatively the intensity ratios of the Ramanscattering arising from the corresponding local structural distortions.PbSc0.5Ta0.5O3 and PbSc0.5Nb0.5O3 differ from each other in the length of coherence of Pb shifts from the O layers,which leads to dissimilarities in the ferroelectric state. The incorporation ofadditional elements in the cation positions heavily influences the incipientferroic species and restrains the formation of proper ferroelectric state, thusfavouring the non-ergodic state. The partial substitution of Ba for Pb andSn4+ for the B-type cations induces additional local structural deformations consisting mainly ofBO6 distortion along the three-fold and four-fold octahedral axes of symmetry, respectively.