ELECTROTRANSPORT IN COBALT MONOXIDE

Cations are generally recognized as the most mobile species in transition metal oxides. The cation migration is responsible for the oxide-gas interface displacement and it can thus be used for the determination of cation transport numbers. The cobalt transference number in cobalt monoxide has been measured at a temperature close to 1000°C and at oxygen partial pressures between 0.004 and 1 atm. The vacancy mobility increases with po2. The effective valency of the diffusing defect remains approximately constant and equal to an average value of two. This implies that cobalt vacancies do not obey one of the fundamental assumptions in Wagner's oxidation theory regarding the equivalence between chemical and electrical work. Zd should thus be introduced as a correction factor for the electrical work just like the correlation factor already is for the chemical work. The same phenomenon is likely to occur in other transition metal oxides. © 1979, The Electrochemical Society, Inc. All rights reserved.