Electrical Transport and Oxygen Exchange in the Superoxides of Potassium,Rubidium, and Cesium

Conductivity, ionic transference number, and chemical diffusion coefficients are determined for KO₂, RbO₂, and CsO₂. Based on such results, a defect‐chemical model is constructed. These superoxides are found to exhibit a total conductivity in the range of 3 × 10^–7 to 5 × 10^–5 S cm^–1 at 200 °C with contributions from ionic and electronic carriers. The ionic conductivity is caused by alkali interstitials and superoxide vacancies as mobile defects, and is found to exceed the n‐type electronic conductivity. ¹⁸O isotope exchange on powder samples (monitoring the gas phase composition) shows that essentially all oxygen can be exchanged. At high pO₂ this largely occurs without breaking of the O–O bond—indicating a sufficient mobility of molecular superoxide species in the solid—and with an effective rate constant that is much higher than for other large‐bandgap mixed conducting materials such as SrTiO₃.