Phase stability of iron oxides epitaxial thin films under O2, CO2 and H2O environmental conditions

Abstract

The phase stability of iron oxide epitaxial thin films (FeO, Fe₃O₄, and γ-Fe₂O₃) under various environmental conditions, specifically O₂, H₂O and for the first time on CO₂, was systematically investigated using synchrotron based in situ grazing incidence X-ray diffraction (GIXRD) and reciprocal space mapping (RSM). We measured the phase transitions of these epitaxial thin films on SrTiO₃ (001) substrates at temperatures ranging from room temperature to 1100 °C, with gas pressures from 10⁻⁹ mbar to 1 bar. Our findings show that the phase stability of the films deviates from previously predicted phase diagrams, only available for O₂ and H₂O, particularly under low partial pressures, suggesting that the thin-film nature and substrate effects significantly influence the phase transitions. These findings highlight the complex interplay between temperature, gas pressure, and substrate role in determining and controlling the phase stability, providing a broader approach for phase engineering in complex oxide thin films.