Structure and properties of (Ba,Ca)TiO₃ ceramics prepared using (Ba,Ca)CO₃ precursors: II. Diffuse phase transition behavior

Abstract

Ferroelectric phase transition in (Ba,Ca)TiO₃ ceramics has been investigated using dielectric measurements. It is shown that samples prepared using (Ba,Ca)CO₃, precursors exhibit diffuse phase transition (DPT) while those prepared by the conventional route show BaTiO₃-type sharp transition. The diffuseness of the phase transition is found to increase with increasing calcium content. The critical exponent for the dielectric stiffness (1/ε') departs significantly from the mean field value of unity and is shown to increase from 1.21 to 1.86 with increasing calcium content. Arguments are advanced to show that the DPT behavior in these ceramics is inexplicable in terms of either the internal stress model due to the absence of 90° domains in fine-grain ceramics or the compositional inhomogeneity model. It is proposed that DPT behavidr is intrinsic to the system and is intimately linked with the appearance of polar phase in the critical regime whose width is shown to increase with increasing Ca content.