Measurement of chemical and tracer diffusion coefficients of oxygen in La 2Cu 0.5Ni 0.5O 4+ δ

Abstract

In mixed electronic and ionic conductors O 2−/e − (MIEC), where the electronic conductivity is dominant, the determination of the oxygen diffusion coefficient is an essential feature. In the present paper, the oxygen chemical diffusion coefficient D̃ O of a MIEC oxide has been evaluated using the conductivity relaxation method, in the temperature range 773–1173 K. Samples of La 2Cu 0.5Ni 0.5O 4+ δ were selected because of the high value of their surface exchange coefficient. In addition, the oxygen diffusion coefficient D* was determined from the 18O tracer diffusion profile. Finally, the oxygen partial pressure dependence of this compound was determined by thermogravimetric analysis (TGA). On the basis of these three independent experiments, the model of ambipolar diffusion, which describes the diffusion in mixed oxide, has been experimentally verified. For such a determination of the intrinsic diffusion characteristics, dense samples are required.