First‐principles investigation of intrinsic defect formation and diffusion mechanisms in Al ₂ O ₃ –Y ₂ O ₃ oxides

Abstract Current and future high‐temperature materials rely on oxide layers formed during service or applied as coatings to protect components from oxidation‐ and corrosion‐induced damage. Understanding of defect diffusion within these oxides is often lacking, despite the central role of these processes in dictating material performance. This study investigates the intrinsic defect diffusion mechanisms in five oxides within the technologically relevant Y–Al–O system (Al 2 O 3 , Y 3 Al 5 O 12 , YAlO 3 , Y 4 Al 2 O 9 , and Y 2 O 3 ). Using density functional theory calculations, defect formation energies are analyzed under varying oxygen conditions to identify the most dominant defects in these oxides. Based on the formation energies under oxygen‐rich conditions, our investigations into the diffusivity of energetically favorable defects reveal that Al 2 O 3 exhibits the lowest defect diffusivity. In contrast, Y 2 O 3 has the highest defect diffusivity due to its extensive channel structure. Additionally, we observe a trend of increasing diffusivity with higher Y 2 O 3 content in the Y–Al–O series. In particular, results suggest that alloying Al 2 O 3 with Y 2 O 3 should ideally maintain a ratio of more than 5:3 to prevent significant increases in diffusivity and commensurate susceptibility to diffusion‐controlled oxidation and corrosion damage. Ultimately, this research enhances our understanding of intrinsic defect diffusion mechanisms in complex oxides aimed at designing next‐generation materials resistant to degradation in extreme environments.