Chemical diffusion and surface exchange in selected Ln-Ba-Sr-Co-Fe perovskite-type oxides

In this paper, a discussion on determination of chemical diffusion coefficient (D) and surface exchange reaction coefficient (K) was given on a basis of electrical conductivity and mass relaxation experiments, performed for selected Ln-Ba-Sr-Co-Fe perovskite-type oxides. The synthesized materials were analyzed in terms of their basic physicochemical properties (crystal structure, oxygen nonstoichiometry, electrical conductivity). Gathered relaxation-type data were critically analyzed, and a strong effect of the enthalpy of the oxidation process, as well as an influence of the porosity were observed, showing limitations of applicability of these techniques, especially for simultaneous determination of D and K. An additional discussion and results were also given regarding possibility of using X-ray diffraction data, recorded during change of the oxygen partial pressure at elevated temperatures, for evaluation of the considered transport coefficients.