ELECTRICAL CONDUCTIVITY AND CHEMICAL DIFFUSION COEFFICIENT OF STRONTIUM-DOPED LANTHANUM MANGANITES

摘要

Electrical conductivity and chemical diffusion coefficient of Sr-doped lanthanum manganites, La1-xSrxMnO3+/-delta (x = 0.05-0.20), were measured by the de four-probe technique and relaxation type experiments where a sudden change of oxygen chemical potential was imposed on the pre-equilibrated sample and the change of electrical conductivity was followed as a function of elapsed time, A defect model is proposed to elucidate the oxygen partial pressure dependence of the measured conductivity and the reported oxygen nonstoichiometry. The transient conductivity behavior after an abrupt change of oxygen partial pressure was successfully described by a diffusion model with consideration of partial control by surface reaction. The determined chemical diffusion coefficients, of the order of 10(-5) to 10(-4) cm(2) s(-1) at 1000 degrees C, increased with decreased oxygen partial pressure due to the thermodynamic enhancement effect. Using the enhancement factor estimated by combination of the proposed defect model and the ambipolar diffusion theory, the oxygen vacancy diffusion coefficients were derived. High vacancy diffusivity comparable to that of Fe- or Co-based perovskites predicts fast oxide ion diffusion under conditions where the manganites show oxygen deficient type nonstoichiometry. (C) 1996 Academic Press, Inc. [References: 36]