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Theoretical Analysis of Oxygen Vacancy Formation in Zr-Doped BaTiO3

One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO3 is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [Ef(VO)] in Zr-doped and undoped BaTiO3 was performed. The Ef(VO) of Zr-doped BaTiO3 was higher than that of undoped BaTiO3 because the valence of Ti in undoped BaTiO3 easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO3. We also prepared undoped (BaTiO3) and Zr-doped (BaZr0.05Ti0.95O3) ceramic samples sintered under reducing atmosphere (T = 1573 K pO2 = 10-13 MPa). BaZr0.05Ti0.95O3 remained an insulator, but BaTiO3 showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.