Atomic structures of [001] symmetric tilt grain boundaries and their influences on the trapping of oxygen vacancies at grain boundaries in barium titanate were analyzed using static atomistic simulation techniques. It was found that the structures were determined to minimize the deficiency in the coordination numbers of Ti4+ ions and to suppress the structural distortion in the vicinity of the grain boundaries. The excess energy of the grain boundary was dependent upon the number density of the coordination-deficient Ti4+ ions, indicating that the ionic bonds between Ti4+ and O2− ions were responsible for structural stabilization of grain boundary. It was also found that the grain boundary played an important role in trapping oxygen vacancies, which acted as a resistance against the oxygen vacancy’s diffusion. The trapping originates from the presence of irregular O2− sites, where oxygen vacancies energetically prefer to reside, influenced by coordination environment. Based on the detailed analyses on origins of grain boundary energy and the trapping in the vicinity of grain boundaries, new physical ground that correlates grain boundary energy and capability of oxygen-vacancy trapping were provided, permitting the prediction of how many vacancies could be trapped at grain boundaries at the atomic level by micrometer-order measurements of grain boundary energy. Electrical degradation of the BaTiO3 dielectrics used for multilayer ceramic capacitors could be prevented by controlling the characteristics of the grain boundaries to promote oxygen-vacancy trapping at grain boundaries in polycrystalline materials via modifying materials synthesis procedures.

Trapping of Oxygen Vacancy at Grain Boundary and Its Correlation with Local Atomic Configuration and Resultant Excess Energy in Barium Titanate: a Systematic Computational Analysis. T.Oyama, N.Wada, H.Takagi, M.Yoshiya: Physical Review B, 2010, 82[13], 134107