An investigation was made of the influence of photo-excited non-equilibrium electrons in Bi4Ti3O12-δ which contained a high density of O vacancies. With increasing O deficiency, the photocurrent underwent rapid enhancement; accompanied by a marked change in the kinetics. In heavily O-deficient Bi4Ti3O12-δ (δ = 0.45), a non-exponential relaxation of photogenerated carriers was observed, with an increasingly slow decay after cessation of visible illumination with an energy lower than the band-gap. This behavior was similar to that reported for persistent photoconductivity in the layered perovskites, YBa2Cu3O7 and Nd2Ti3O9; both of which resulted from a space charge field established by photo-excited electrons trapped at O vacancies. It was proposed that O vacancies, acting as trapping centers for electrons, were linked to dispersive diffusion in the perovskite blocks which control carrier recombination.

Oxygen Vacancy Migration and Dispersive Photoconductivity in Bi4Ti3O12-δ. M.Osada, M.Tada, M.Kakihana, Y.Noguchi, M.Miyayama: Japanese Journal of Applied Physics, 2004, 43[9B], 6649-52