Relaxor ferroelectrics

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Abstract
This article attempts to review a number of macroscopic measurements which have been used to explore the electrical, mechanical, thermal, and optical characteristics of relaxor ferroelectrics and to authenticate the compositional heterogeneity model which was first proposed by G.A. Smolenskii to describe these materials. In this connection the work of N. Setter on order disorder in lead scandium tantate is discussed to clearly establish the role of compositional heterogeneity. To demonstrate the very wide temperature range above the dielectric permittivity maximum Tm over which large values of RMS polarization persists, electrostrictive spontaneous strain and quadratic electro-optic measurements on lead magnesium niobate and on the tungsten bronze structure ferroelectric barium strontium niobate are introduced. In order to validate the hypothesis that the polar micro regions which exist above Tm are in dynamical disorder, measurements of the field induced electrostriction are reviewed. From the aging behavior of suitably doped relaxor compositions it is suggested that because of internal heterogeneity local and global symmetries differ in the relaxor and the consequences of these differences are discussed with respect to the poling: depoling behavior and to the low temperature dispersion in lead barium niobate bronze structures.