Defect chemistry in perovskite ferroelectrics-History, present status, and future prospects-

Perovskite ferroelectrics such as BaTiO3 and PbTiO3 provide various functions arising from spontaneous polarization. Here, the history, present status, and future prospects of the defect chemistry for BaTiO3 are described. Even for non-doped samples, unintentional impurities including Fe govern the defect chemistry and its related properties. By solving multiple nonlinear equations employing the thermodynamic data set reported, majority/minority defect-concentration diagrams are available not only in a high-temperature equilibrium state but also in a low-temperature quenched one. As an example, the defect diagrams of Ba(Ti,Ca)O-3 and Ba(Ti,Mn)O-3 are shown, and the roles of fixed valence (Ca) and variable-valence (Mn) acceptors are explained. I also introduce an example of the defect control in BaTiO3 single crystals; an activation of visible-light photovoltaic effect, where two redox potentials derived from Fe2+ and Fe3+ act as scaffolds for generating electron-hole pairs. (C)2021 The Ceramic Society of Japan. All rights reserved.