Mixed Electrical Conduction in the Fluorite‐Type Ce1 − x Gd x O 2 − x / 2

The solid solutions exhibit high ionic conduction due to the migration of O 2− 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 where is a constant corresponding to the oxygen partial pressure at which the ionic transference number of the solid solution becomes 0.5. From the temperature dependence of , partial molar enthalpy changes for the reduction of are calculated.