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The solid solutions exhibit high ionic conduction due to the migration of O2− ions via oxygen ion vacancies. The emf of a galvanic cell,, is measured within the temperature range between 700° and 800°C as a function of . At such high oxygen pressures as in air, the emf changes according to indicating the ionic transference number in the solid solution is unity. With decreasing oxygen pressure, however, the observed emf becomes smaller than the theoretical value. This indicates the onset of electronic conduction generated by the reduction of the solid solution. The dependence of the emf on is described by
Kudo et al. (Mon,) studied this question.