Partial conductivities in SrTiO3: Bulk polarization experiments, oxygen concentration cell measurements, and defect-chemical modeling

Knowledge of the exchange kinetics of O-2 in SrTiO3 allows us to design appropriate strategies to separate the ionic and the electronic conductivity, In the low-temperature range, where the overall surface reaction is very slow compared to bulk diffusion and measuring time, electrochemical cells of the type Pt/SrTiO3/Pt are self-blocking and self-sealing and a Wagner-Hebb-type polarization succeeds without the necessity of using selectively blocking electrodes, In the present study the ionic conductivity data obtained for Fe-and Ni-doped SrTiO3 in this way are compared to data obtained from the analysis of the oxygen partial pressure dependence of the total conductivity as well as to defect-chemical calculations. In complete contrast to the low-temperature situation, at high temperatures, where the surface reaction is fast, the emf technique is conveniently applicable, Results are presented for Pt, O-2/SrTiO3/O-2, Pt cells, The conductivity behavior of SrTi(Fe)O-3 as a function of temperature (20 degrees-1000 degrees C) is complex, due to partially frozen-in equilibria, but even details can be quantitatively understood in terms of a simple defect chemistry, The turnover of the diffusion-controlled regime to the surface-reaction-controlled regime can be shifted to significantly lower temperatures by using YBa2Cu3O7-delta electrodes.