Energetics and diffusion kinetics of point defects in MnCr2O4 spinel from first principles

Abstract

MnCr2O4 spinel is a component of the multilayered oxide film which forms atop austenitic steel alloys under high-temperature corrosion conditions. In this work, the thermodynamics and kinetics of cationic and anionic point defects in this spinel are examined through density functional theory calculations. To model the physical conditions of the corrosion process more closely, temperature is accounted for by adjusting the chemical potential of each species to fit experimentally determined values. We find that manganese is the most mobile species - migrating through the lattice via a vacancy mediated mechanism. Oxygen migration can occur via vacancy mediated or three-body interstitial mechanisms with similarly low barrier heights, highlighting the possibility of oxide growth at the film/alloy interface due to the high oxygen permeability. Furthermore, a number of more complex migration mechanisms involving substitution and antisite defects are evaluated for their potential contribution to cation mobility.