Examination of spinel and nonspinel structural models for gamma-Al2O3 by DFT and rietveld refinement simulations

Despite the widespread use of gamma-Al2O3, there is still considerable disagreement over the nature of its structure due to both its poor crystallinity and differing preparation techniques during experimentation. Using density-functional theory (DFT) calculations and Rietveld simulations and refinement, the structure of three spinel-related models and a recently proposed nonspinel model were studied in reference to synchrotron X-ray powder diffraction (SXPD) patterns. The spinel-based structural models represent the structural features of gamma-Al2O3 better than the nonspinel model. The major failure of the nonspinel model is that the model cannot reproduce the SXPD reflection originating from tetrahedral aluminum. The Rietveld-refined spinel model can accurately reproduce the lattice parameters and other structural features of gamma-Al2O3, and it can generate a consistent diffraction peak at 2theta which lies between the splitting peaks of the experimental pattern that are originated from the disordered tetrahedral aluminum cations.