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

抄録

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)O₃ and Ba(Ti,Mn)O₃ 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.