Nonstoichiometry in strontium titanate as an example of alkaline earth titanates was discussed in terms of Sr/Ti ratio and dopant concentration and extended defect existence. For some dopant concentrations and titanium or strontium excess a self-compensation of cation and anion vacancies could be observed, leading to unusual pressure dependencies of electrical conductivity.
The defect structure and the chemical diffusion coefficients Dchem were determined in Ti excess undoped and Nb doped SrTiO3 thin films as well as in undoped SrTiO3 single crystal (1 0 0). The observed difference in Dchem was explained basing on the defect structure models. In both cases of SrTiO3 thin films, the low-mobility strontium vacancies are the predominant defects, while in case of SrTiO3 single crystal the high-mobility oxygen vacancies are responsible for the much faster oxygen gradient decay.
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