Abstract
In the previous study, we have discovered 21 novel biocompatible lead-free piezoelectric materials in perovskite-type oxide through first-principles calculations. The purpose of this study is the prediction of phase diagram to support the fabrication of the discovered novel materials. The cubic stable structure was estimated and the phonon properties were analyzed. Then, the soft mode was identified with eigenvalue and the asymmetric stable structure caused by the soft mode was evaluated. Total energy and spontaneous polarization of some stable structures were approximated by Gibbs function based on a thermodynamic theory which can be utilized for the prediction of phase diagram. The proposed method was applied to an existing piezoelectric material, BaTiO_3 and energy distribution was presented.
