X-RAY AND PHENOMENOLOGICAL STUDY OF LANTHANUM-MODIFIED LEAD ZIRCONATE-TITANATES IN THE VICINITY OF THE RELAXOR PHASE-TRANSITION REGION

X-ray diffraction analyses of chemically derived Pb1-xLa(x)(Zr0.65Ti0.35)1-x/4O3 powders were combined with a phenomenological theory to investigate the corresponding single-crystal thermodynamic properties of compositions approaching the relaxor ferroelectric phase transition region (x = 0-0.04). The temperature dependence of the electrostrictive strain component, x4, could be described by the Landau-Ginsburg-Devonshire phenomenological theory taking T(c) = 357-degrees-C independent of La content (x). The single-domain, single-crystal elastic Gibbs free-energy density was calculated as a function of temperature and composition. The calculated results were discussed in relation to a simple superparaelectric model of relaxor behavior involving the temperature stabilization of noninteracting polar microregions.