Approximations to defect chemistry in Bi₄Ti₃O₁₂

Bismuth titanate (Bi₄Ti₃O₁₂ or BiTO) is known for its high resistance to dielectric fatigue and relatively large remnant polarization. Owing to these characteristics, it has been applied in FeRAM memory. BiTO is also known to be a potential ionic conductor. In both applications, crystalline defects play an important role. In this work, a standard thermochemical equilibrium procedure is used to analyze defect chemistry in BiTO. The results indicate a strong oxidized state. To obtain a reduced condition, extremely low oxygen partial pressures and high temperatures have to be achieved. Even at normal conditions, results show a relatively high concentration of holes, which is in agreement with the p-type leaking experimentally observed, relatively high concentration of oxygen vacancies, which suggest the potential application of BiTO as ion conductor, and relative high concentration of bismuth vacancies, in accordance with the known problem of bismuth volatilization observed during the processing of this material.