Influence of synthesis process on the AC response of PLZT (8/65/35) ferroelectric ceramics

AC conductivity measurements have been carried out to study the dielectric characteristics of a ferroelectric PLZT (8/65/35). The initial powders were synthesized by two different methods: conventional mixed oxides and a chemical coprecipitation method. In both cases, the final ceramic bodies were obtained by an uniaxial hot-pressing step. The grain and grain boundary responses have been separated and a mixture of ionic-electronic conductivity was evaluated from the Arrhenius dependence. The preparation techniques led to different absolute conductivity values for each contribution (grain, sigma(g), or grain boundary, sigma(gb)). The samples prepared by the mixed oxide method (MO) showed a higher bulk conductivity than those prepared by the coprecipitation method (CP). This result was explained taking into account the different concentration of charge carriers in MO than CP samples, influenced by the PbO content in the grain boundary. The dielectric analyses showed classical ordinary relaxor-dielectrics with a diffuse phase transition, which was markedly larger in the oxide-milled method (MO). The conductive mechanisms and their influence on the dielectric behavior were studied and led to the conclusion that they affect the dielectric permittivity measurements. The dielectric permittivity without the conductivity component showed a phase transition with lower dispersion for both preparation techniques. (C) 2002 Elsevier Science Ltd. All rights reserved.