High Temperature Diffusion of Oxygen in Chromite

Molecular dynamics was used to calculate the diffusion coefficient of oxygen over a temperature range of 900–1700K. The chromite (FeCr₂O₄) system used consisted of 448 ions in a spinel structure. The spinel consisted of Fe²⁺ in tetrahedral sites and Cr³⁺ ions in octahedral sites surrounded by O²⁻ ions. Schottky defects were made in the system by removing 10 oxygen ions, 4 iron ions and 4 chromium ions. The trajectory files from the simulations were examined for oxygen movement via a vacancy hopping mechanism and the mean-squared displacement of oxygen was plotted against time. A linear fit was performed to the plots and Einstein’s relationship was used to derive the diffusion coefficient from the gradient. The diffusion coefficients were then plotted against temperature and an Arrhenius expression was fitted to the trend and compared with the experimental trend calculated by Takada & Adachi.