Detailed x-ray diffraction analyses and correlation of microstructural and electromechanical properties of La-doped PZT ceramics

The influence of the La-concentration (0.1-8 mole-%) on the F-R/F-T-ratio and the c/a-ratio of mixed oxide derived stoichiometric and 3 mole-% PbO excess containing PZT with a Zr/Ti-ratio near the morphotropic phase boundary (53/47) was investigated by quantitative X-ray diffraction analysis. Temperature dependent X-ray diffraction measurements showed a decrease of the Curie-temperature for La-additions > 0.5 mole-% but an increase for very low La-amounts (0.1 and 0.2 mole-%) in comparison to undoped samples. Obviously this phenomenon indicates the influence of La-dopants on the vacancy concentration and thereby on the stability of the crystal structure. The change in vacancy concentration leads to a different densification behavior for undoped and doped samples which could be shown by dilatometric measurements. The observations were finally correlated to measurements of dielectric constants and coupling factors which additionally show a strong dependence on the PbO excess and the microstructure (porosities, grain sizes and chemical inhomogeneities) of PZT ceramics.