Influence of Oxygen Vacancies on the Polarization Properties in Bi₄Ti₃O₁₂ Ferroelectric Single Crystals

Measurements of the leakage-current and polarization properties in bismuth titanate (Bi4Ti3O12) along the a axis show that the crystals grown in air followed by air annealing at 700oC had a superior remanent polarization of 48 μC/cm2 as well as a low leakage current density of the order of 10-9 A/cm2. The annealing at a high oxygen partial pressure of 35MPa (700oC) resulted in a higher leakage current, indicating that electron holes arising from the incorporation of oxygen at oxygen vacancies act as detrimental carriers for electrical conduction at room temperature. A crystal growth under high-pressure oxygen atmosphere and subsequent annealing at a moderate oxygen partial 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.