DETERMINATION OF OXYGEN NONSTOICHIOMETRY AND DIFFUSIVITY IN MIXED CONDUCTING OXIDES BY OXYGEN COULOMETRIC TITRATION .2. OXYGEN NONSTOICHIOMETRY AND DEFECT MODEL FOR LA0.8SR0.2COO3-DELTA

The oxygen nonstoichiometry of La0.2Sr0.2CaO3-delta has been determine d as a function of oxygen partial pressure and temperature using a hig h-temperature coulometric titration cell. For each measured value of t he oxygen chemical potential, the oxygen nonstoichiometry is found to be nearly independent of temperature. The equilibrium partial energy a nd entropy associated with oxygen incorporation have been determined a s a function of oxygen nonstoichiometry and temperature. The results a re interpreted in terms of a model in which it is assumed that conduct ion Electrons, created during vacancy formation, gradually fill electr on states in a wide electron band. A new relation between vacancy conc entration, temperature. and oxygen partial pressure has been formulate d which does not have the familiar appearance of a mass action type of equation.