Oxygen nonstoichiometry and transport properties of strontium substituted lanthanum ferrite

This study presents an investigation of the properties of (La0.6Sr0.4)0.99FeO3-δ (LSF40) covering thermomechanical properties, oxygen nonstoichiometry and electronic and ionic conductivity. Finally, oxygen permeation experiments have been carried out and the oxygen flux has been determined as a function of temperature and driving force.

The electrical conductivity was measured using a 4 probe method. It is shown that the electrical conductivity is a function of the charge carrier concentration only. The electron hole mobility is found to decrease with increasing charge carrier concentration in agreement with recent literature. Values of the chemical diffusion coefficient, DChem, and the surface exchange coefficient, kEx, have been determined using electrical conductivity relaxation.

At 800?CDChem is determined to be 6.2x10-6cm2s-1 with an activation energy of 137kJmol-1. The surface exchange coefficient is found to decrease with decreasing oxygen partial pressure. Oxygen permeation experiments were carried out. The flux through a membrane placed between air and wet hydrogen/nitrogen was JO2~1.8x10-6molcm-2s-1 (corresponding to an equivalent electrical current density of 670mAcm-2).

The oxygen permeation measurements are successfully interpreted based on the oxygen nonstoichiometry data and the determined transport parameters.