EFFECTS OF QUENCHED DISORDER ON LA-MODIFIED LEAD-ZIRCONATE-TITANATE -LONG-RANGE AND SHORT-RANGE ORDERED STRUCTURALLY INCOMMENSURATE PHASES, AND GLASSY POLAR CLUSTERS

Structure-property relationship studies have been performed in the La- modified lead zirconate titanate (PLZT) solution as a function of quen ched La impurity content and Zr/Ti ratio by transmission electron micr oscopy, lattice imaging, and dielectric spectroscopy. Investigations w ere performed for 65/35 less than or equal to Zr/Ti less than or equal to 90/10. These investigations have demonstrated a general trend in d omain structure and polar order with increasing quenched impurity conc entration. For Zr/Ti ratios of 90/10 and 85/15, a structurally incomme nsurate antiferroelectric (AFE(in)) state was found to be stabilized w ith increasing La. Temperature dependent investigations demonstrated t hat the incommensurate structure becomes pinned into long-time metasta ble states, rather than transforming to a commensurate phase. Also, th e modulation wavelength (lambda) was found to increase significantly w ith increasing Ti. When lambda increased to similar to 40 Angstrom, po lar clusters began to condense from the AFE(in) order. For Zr/Ti ratio s of 80/20 and 65/35, increasing quenched disorder was found to result in the evolution of polar order through a common sequence of domainli ke states including polar clusters, tweedlike structures, and normal m icron-sized polydomain structures. These results, in conjunction with dielectric spectroscopy, demonstrate a crossover between a long-period incommensurately modulated state and a relaxer ferroelectric state wi th increasing quenched disorder. Clearly, both quenched disorder (i.e. , random fields) and competing polar orderings (i.e., frustration) und erlay the unique behaviors of PLZT. (C) 1998 American Institute of Phy sics.