Oxygen stability and leakage current mechanism in ferroelectric La-substituted Bi4Ti3O12 single crystals

We have investigated the effects of La substitution on the oxygen stability, defects, leakage current and polarization properties in ferroelectric bismuth titanate (Bi4TiO12) by measuring the properties of single crystals and by ab initio electronic structure calculations. It is shown that electron holes arising from the incorporation of oxygen at oxygen vacancies act as detrimental carriers for leakage current at room temperature for the crystals of BiT and La-substituted BiT. La substitution is effective for reducing oxygen vacancies and thus electron holes, which is attributed to an excellent insulating property observed for La-substituted crystals. High-pressure oxygen annealing is demonstrated to improve the remanent polarization of La-substituted crystals.