Point Defects and Sintering of Lead Zirconate‐Titanate

Abstract

The crystal chemistry of point defects in lead zirconate‐titanate is discussed. The results are used to interpret sintering and grain‐growth behavior. Lattice vacancies are created thermally, by substitutional impurities with incorrect valences, and by changes in stoichiometry. Charged O vacancies are introduced when Al 3+ replaces Ti 4+ , and charged Pb vacancies occur when Nb 5+ replaces Ti 4+ . These vacancies are believed to be associated with the impurity ions and cause them to be adsorbed at grain boundaries. This behavior retards grain growth and thereby expedites densification. Aluminum ions (deficient valence) compensate for niobium ions (excess valence). These “paired” defects are not associated with vacancies and are not adsorbed; thus, they do not impede grain growth. Sintering follows Coble's model of bulk diffusion of vacancies from pores to grain boundaries. Oxygen vacancies are believed to be the slowest‐moving species. Aluminum: niobium compensation is confirmed by ferroelectric measurements. Doping with Al decreases the mobility of ferroelectric domain boundaries, whereas Nb increases it. Doping with both ions produces ferroelectric properties similar to those of the undoped material.