Relationships among ferroelectric fatigue, electronic charge trapping, defect-dipoles, and oxygen vacancies in perovskite oxides

Using electron paramagnetic resonance, it is shown that the reduction of the switchable polarization in BaTiO₃ crystals by repeated polarization reversals (fatigue) is accompanied by the trapping of electronic charge at isolated acceptor impurities and atomic scale distortions in the perovskite oxygen octahedron. The distortions are proposed to entail nearby oxygen vacancies. Our results suggest that the suppressed polarization state arises by trapping electronic charge carriers at domain walls; the trapped electronic charge can become thermally stabilized by fatigue-induced distortions in the oxygen octahedron. The octahedron distortions are shown to be unique to fatigue-induced degradation; they are not observed in BaTiO₃ capacitors that have an optically-induced suppressed polarization state.