With a specific focus on defects formed from H atoms and oxygen vacancies (VO) in perovskite-type oxide, stability and stable valence states of complex defects formation processes within BaTiO3 were studied by using first-principle density-functional theory calculations. It was found that H atoms diffused as protons (H+) into interstitial sites in BaTiO3, whereas these atoms when trapped at centers of VO sites converted to negatively ionized states (H−). It was also found that H atom trapping at VO sites occurred only in n-type carrier-rich environments without carrier compensation of VO2+ and H+. If carrier electrons were compensated, H+ ions were excluded from VO2+ sites due to the repulsive Coulomb potential existing between the H+ ion and the positively charged VO2+ site. Difficulties in the calculation of the diffusion-energy diagram for H atoms, involving essential changes in the stable valence states during the diffusion process, were considered and a practical solution was presented.

Negatively Charged Hydrogen at Oxygen-Vacancy Sites in BaTiO3: Density-Functional Calculation. Y.Iwazaki, T.Suzuki, S.Tsuneyuki: Journal of Applied Physics, 2010, 108[8], 083705