Anomalous Structure and Dielectric Properties of BaTiO₃-CaTiO₃ System Ceramics Composites

Abstract

BaTiO₃-CaTiO₃ (BCT) system ceramics composites with various chemical compositions were prepared by the conventional solid state reaction, and their crystal structures and electric properties were investigated on a function of a chemical composition. Below Ca contents of 23 at%, BCT ceramics was a single solid solution with tetragonal phase while above Ca contents of 23 at%, two phases of BCT ceramics coexisted, i.e., tetragonal BCT ceramics with Ca content of 23 at% and orthorhombic BCT ceramics with Ca content of over 95 at%. In the coexistence region of the two phase, some structural and electrical anomaly were observed. In this region, lattice parameter of Ba-rich BCT ceramics must be constant, but with increasing Ca content, a-axis increased while c-axis decreased. As a result, c/a ratio decreased with increasing Ca contents, and approached to 1.0 over the Ca content of 50%. The measurement of the chemical composition in this region revealed that the chemical composition of Ba-rich BCT ceramics was always constant. Thus, the structural anomaly was independent of the chemical composition. Moreover, the measurement of the dielectric properties showed some anomaly in this region. Especially, polarization (P) vs. electric field (E-field) curves exhibited that remanent polarization (Pr) decreased with increasing Ca content, and at the Ca content of 50%, a clear double hysteresis loop was observed. To explain the above some anomaly, a model that the anisotropic residual stress can produce a new antiferroelectric phase was proposed.