Electrical Properties of Nb-Doped PZT 65/35 Ceramics: Influence of Nb and Excess PbO

The effect of Nb and excess PbO on the structural and electrical properties of conventionally prepared Nb-doped PZT 65/35 ceramics has been studied in this work. It is found that, from excess PbO contents as high as 4 mol%, the solubility limit of Nb in PZT occurs below 4 mol%, while a secondary prevoskite-like phase develops in the dielectric system for a further increase of Nb content. The ferroelectric and piezoelectric properties (permittivity, ferro-paraelectric phase transition, polarization, electromechanical coefficients) of such materials are thus found to be strongly dependent on the degree of densification and structural phase development during sintering at high temperatures. In particular, the nature of the ferro- to para-electric phase transition is in these materials noted to better fit a generalized rather than Smolenskii-Isupov equation, the former being appropriate for the characterization of non-purely diffuse transitions. In nice agreement with the Bokov model, substitution of Nb^{5 +} for (Zr,Ti)^{4 +} is found to induce only poorly diffuse phase transition in these materials. The electrical properties reported in this work are in magnitude comparable to those exhibited by PZT-based materials.