Interstitialcy-Mediated Transport in Hematite

Abstract Defect transport mechanisms drive the performance of materials in both energy storage and generating systems, where iron oxide systems are of particular interest with use cases in both realms. Previous studies of α-Fe2O3 (hematite) determined that the primary point defects at elevated temperature are O vacancies and Fe interstitials, and these defects determine transport rates at temperatures >850 °C. However, in advanced nuclear reactor designs, operating temperatures will range between 400 and 800 °C. In this study, we utilize isotopic tracers and atom probe tomography to measure diffusivities at lower temperatures relevant to nuclear energy generating systems. Supported by a density functional theory informed rate theory model, we find a change from vacancy to interstitialcy-mediated transport at <800 °C in the anion lattice. Transport in the cation lattice remains interstitially driven.