Electronic properties of polycrystalline LaFeO3. Part II: Defect modelling including Schottky defects

The electrical conductivity of polycrystalline LaFeO3 is reported as a function of temperature. The conductivity of LaFeO3 was shown to be affected by annealing for extended periods (about one week) at temperatures above 1000 deg C prior to the conductivity measurements. Higher annealing temperatures resulted in higher conductivity. This effect was explained by the formation of Schottky cation defects, which act as electron acceptors, leading to an increasing conductivity with increasing annealing temperature. Below 1000 deg C, the conductivity was unaffected by the annealing temperature, probably due to the low mobility of cation vacancies. A model for the defect chemistry and conductivity of LaFeO3, including the formation of Schottky defects is proposed. The model reproduces quantitatively the dependence of the conductivity with respect to the partial pressure of oxygen at 1000 deg C. The electronic mobilities of the charge carriers in the material were determined by the conductivity of La0.99Sr0.01FeO3, where the charge carrier concentration is given by the dopant level. The model also predicts that the concentration of p-type charge carriers in air is increasing with temperature due to the formation of Schottky defects, for a limited temperature interval above 1000 deg C.