Post heat treatment effect on crystal structure and ferroelectricity of (1 − x)(Bi,K)TiO₃–xCaTiO₃ solid solution epitaxial films grown by hydrothermal method

Abstract

The effect of post heat treatment on the crystal structure, Curie temperature, and ferroelectric properties of hydrothermally grown epitaxial films of (1 − x)(Bi,K)TiO₃–xCaTiO₃ (x = 0–0.26) was investigated. The out-of-plane c-axis lattice parameter of the post-heat-treated films decreased compared to that of the as-deposited films for all x values. It decreased with the increase in x value in the single-phase region (x = 0–0.12). However, it became almost constant for the film above x = 0.18, coexisting region with the second phase. The solubility limit of CaTiO₃ in (Bi,K)TiO₃ remained almost unchanged after the heat treatment. In the single-phase region, the phase transition temperature from ferroelectric to paraelectric phase (T_c) decreased from 780 °C for the film with x = 0 to 490 °C for the film with x = 0.12. The heat treatment caused a significant decrease in remnant polarization (P_r) and coercive field (E_c) values, and almost eliminated the imprint of P-E hysteresis loops became almost zero by this heat treatment. These results demonstrate that the crystal structure and ferroelectric properties of these films were altered by the post heat treatment.