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 desig n appropriate strategies to separate the ionic and the electronic cond uctivity, In the low-temperature range, where the overall surface reac tion is very slow compared to bulk diffusion and measuring time, elect rochemical cells of the type Pt/SrTiO3/Pt are self-blocking and self-s ealing and a Wagner-Hebb-type polarization succeeds without the necess ity of using selectively blocking electrodes, In the present study the ionic conductivity data obtained for Fe-and Ni-doped SrTiO3 in this w ay are compared to data obtained from the analysis of the oxygen parti al pressure dependence of the total conductivity as well as to defect- chemical calculations. In complete contrast to the low-temperature sit uation, 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 a s a function of temperature (20 degrees-1000 degrees C) is complex, du e to partially frozen-in equilibria, but even details can be quantitat ively understood in terms of a simple defect chemistry, The turnover o f the diffusion-controlled regime to the surface-reaction-controlled r egime can be shifted to significantly lower temperatures by using YBa2 Cu3O7-delta electrodes.