Oxygen non-stoichiometry and oxygen diffusivity of mixed conducting perovskites

An oxygen coulometric titration cell has been designed to measure non-stoichiometry and oxygen diffusivity of mixed oxygen ion and electronic conducting, La0.8Sr0.2CoO3-δ. Chemical diffusion data, combined with oxygen non-stoichiometry data, δ, show that the oxygen vacancy diffusion coefficient is 5.25*e -(132±7 KJ/mol)RTcm2/s, and independent of the oxygen partial pressure, P01. In addition, it is found that log(δ) is linearly related to log(P01) with slope of -0.23±0.02. The entropy associated with oxygen incorporation can be modelled with the configurational entropy of the oxygen vacancies. No electronic entropy contribution is observed. The energy of oxygen incorporation decreases almost linearly with increasing oxygen stoichiometry. Both energy and entropy data agree with a model in which electrons gradually fill electron states in a broad electron band. From the data an empirical relation between vacancy-concentration, temperature and oxygen partial pressure can be formulated, which deviates from mass action behavior.