The influence of a powder processing technique on chemical homogeneity and the diffuse phase transition behaviour of Ba_0.9Ca_0.1TiO₃ ceramics

Abstract

Ba_0.9Ca_0.1TiO₃ ceramics have been fabricated using powders obtained by calcining mixtures of (i) BaCO₃, CaCO₃ and TiO₂ and (ii) Ba_0.9Ca_0.1CO₃ and TiO₂. The precursor Ba_0.9Ca_0.1CO₃ was prepared by a wet technique to ensure homogeneous mixing of Ba and Ca ions at the atomic level. DTA analysis of solid state thermochemical reactions in the two types of mixtures shows that the temperature of reaction completion is 140 degrees C lower for the mixture containing the precursor carbonate solid solution. XRD results indicate better chemical homogeneity for powders obtained by the new route. A powder diffraction pattern for Ba_0.9Ca_0.1TiO₃ has been theoretically computed assuming partial substitution of Ba²⁺ by Ca²⁺. The theoretically predicted intensities are in good agreement with those experimentally observed for powders prepared by the precursor route only. Better chemical homogeneity with respect to the distribution of Ca²⁺ ions leads to more pronounced diffuse phase transition in Ba_0.9Ca_0.1TiO₃ ceramics.