The electronic structure, formation energy, and transition energy levels of intrinsic defects were studied using the density-functional method within the generalized gradient approximation for neutral and charged oxygen vacancy in CaCu3Ti4O12 (CCTO). It was found that oxygen vacancies with different charge states can be formed in CCTO under both oxygen-rich and poor conditions for nonequilibrium and higher-energy sintering processes; especially, a lower formation energy was obtained for poor oxygen environment. The charge transition level (0/1+) of the oxygen vacancy in CCTO was located at 0.53eV below the conduction-band edge. The (1+/2+) transition occurs at 1.06eV below the conduction-band edge. Oxygen vacancies of Vo1+ and Vo2+ were positive stable charge states in most gap regions and can act as a moderately deep donor for Vo1+ and a borderline deep for Vo2+, respectively. The polarization and dielectric constant were considerably enhanced by oxygen vacancy dipoles, due to the off-center Ti and Cu ions in CCTO.

Influence of Oxygen Vacancy on the Electronic Structure of CaCu3Ti4O12 and its Deep-Level Vacancy Trap States by First-Principle Calculation. H.B.Xiao, C.P.Yang, C.Huang, L.F.Xu, D.W.Shi, V.V.Marchenkov, I.V.Medvedeva, K.Bärner: Journal of Applied Physics, 2012, 111[6], 063713