DEFECT INTERACTIONS, STATISTICAL THERMODYNAMIC AND ELECTRONIC TRANSPORT IN IONIC NONSTOICHIOMETRIC OXIDES

In this paper, we discuss the effects of the defect interactions on th e thermodynamic properties and electronic transport of nonstoichiometr ic oxides. We first show that two limited thermodynamic behaviours can be distinguished depending on whether the oxide has a metallic type e lectronic conduction or a hopping electronic conduction. In the first case, the interactions are expected to be short ranged because of the screening of the conduction electrons, while they are Coulombic in the second case. This paper is limited to this last case, exemplified mai nly by M(1-x)O (M = Co, Mn,..) cubic oxides. Next, we analyse the two approximated methods usually used in this held, the ideal mass action law method and the Debye Huckel theory, and we show that they are both insufficient to accurately describe these compounds. We finally show by means of Monte Carlo simulations that a simple model in which point defects interact through a unique dielectric constant allows us to re nder an account of the main features of the thermodynamic and electron ic transport properties of these oxides.