THE EQUILIBRIUM BETWEEN WATER-VAPOR, PROTONS, AND OXYGEN VACANCIES INRARE-EARTH-OXIDES

The electrical conductivity of Nd2O3 and Sm2O3 doped with 1 and 2 mol % CaO respectively, and LaGdO3 doped with 5 mol % BaO has been measure d as a function of p(O-2), p(H2O) and temperature. Computer fitting of the data to a simple model allows determination of entropy and enthal py terms for the defect equilibrium between water vapour, oxygen vacan cies and protons, together with the pre-exponential term and the activ ation enthalpy of the charge carrier mobilities. The entropies and ent halpies for these and other rare earth sesquioxides are compared to th ose of perovskites.