Evaluating the accuracy of common γ-Al<inf>2</inf>O<inf>3</inf> structure models by selected area electron diffraction from high-quality crystalline γ-Al<inf>2</inf>O<inf>3</inf>

Single crystal and textured polycrystalline γ-Al2O3 thin films were synthesized by oxidation of NiAl(110) in air at 850 °C for 1 and 2 h, respectively, and used to evaluate the accuracy of two spinel-based and two nonspinel models by comparison of selected-area electron diffraction (SAED). The lattice interplanar distances derived from the polycrystalline SAED pattern most closely matched the cubic spinel γ-Al2O3 model. The single-crystal SAED spot pattern showed symmetry consistent with both the cubic spinel and tetragonal nonspinel models, however, the Al cation distribution better matched the cubic spinel model based on the relative intensities of diffraction spots. Our work indicates that the traditional cubic spinel model is a more accurate model of γ-Al2O3 than the other models considered. The spinel-based monoclinic model is also more accurate than the monoclinic nonspinel model. The understanding of the relative accuracy of the different models is key for simulating γ-Al2O3 containing systems and is of general interest for the metal oxide and ceramic communities.