Normal to relaxor ferroelectric transformations in lanthanum-modified tetragonal-structured lead zirconate titanate ceramics

Lanthanum modified lead zirconate titanate (PLZT) ceramics near a crossover between normal and relaxer ferroelectric states for Zr/Ti ratios of 40/60, 20/80, and 0/100 were investigated by dielectric spectroscopy, Sawyer-Tower polarization techniques and transmission electron microscopy. It was found possible to induce a relaxer state in each of these tetragonal PLZT compositional sequences with increasing La content. The transformation between normal and relaxer-like behaviors was found to be associated with a domain evolution from normal micron-sized domains, to tweed-like subdomain structures, and finally to polar nanodomains. A spontaneous relaxer to normal transformation was found near a critical La content in each compositional sequence. Temperature dependent polarization studies revealed a field-induced relaxer to normal ferroelectric transition at temperatures above that of the spontaneous transformation. (C) 1996 American Institute of Physics.