We have investigated the defect structure in bismuth titanate (Bi4Ti3O12) through high-temperature neutron powder diffraction analysis and ab-initio electronic structure calculations. It is shown that the vacancies of Bi and oxide ions are created preferentially in the perovskite layers rather than in the Bi2O2 layers. Measurements of the leakage-current properties of the single crystals demonstrate that electron holes arising from the incorporation of oxygen at the vacancies of oxide ions act as detrimental carriers for electrical conduction at room temperature. A crystal growth under high oxygen pressure is proposed to be advantageous for suppressing the vacancy formation and for attaining a large remanent polarization as well as a high insulating property of the Bi4Ti3O12 system.
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Noguchi et al. (2005) studied this question.