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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.

Thermally stimulated current (TSC) and electron paramagnetic resonance (EPR) spectroscopies have been used to examine the role of defects in BaTiO3 capacitors that have been subjected to an electric field at elevated temperatures (an accelerated aging process). The aging process caused a reduction in the insulation resistance of the ferroelectric capacitor and induced a voltage offset in its polarization-voltage hysteresis loop. The TSC measurements following resistance degradation show the displacement of positively charged oxygen vacancies and the motion of bulk trapped charge. It is found that the aging process is accompanied by a significant amount of charge trapping that appears to be locally charge compensated. EPR measurements show that some of the trapped charge is associated with changes in the oxidation state of acceptor impurities. Last, it is shown that some of the trapped charge in the ferroelectric is directly associated with the net polarization.