PROCESSING AND PROPERTIES OF PB(MG1 3NB2/3)O3-PBZRO3-PBTIO3 CERAMIC RELAXORS/

The shrinkage phenomenon during the reaction-sintering of PMN-PZT from low-temperature pre-reacted 3PbO + MgNb2O6 + PZT powder mixtures has been studied. It was assumed that the pre-reaction treatment leads to the formation of a pyrochlore phase containing very active MgO small p articles, and that the strong shrinkage occurring up to 800-degrees-C took place by the diffusion of Mg2+ cations into the pyrochlore phase particles, thus controlling the reaction-sintering shrinkage phenomeno n. Above that temperature the densification was enhanced by a liquid-p hase sintering process. The ceramics sintered at 1050-degrees-C for 2 h showed approximately 96% of the theoretical density, and the dielect ric constant of such a sintered ceramic showed a maximum value of 1700 0 at 1 kHz. It was also found that the dielectric constant decreased w ith increasing grain size. Although the role of PZT in enhancing the d ielectric constant of otherwise low-purity PMN ceramics is not clear, the increase in K is assumed to be a solid-solution effect. The presen ce of impurities and the PbO stoichiometry could be influencing the no t too high dielectric constant value of PMN-PZT ceramics.