Resolving Atomic Structure of γ-Alumina: A Non-Spinel Phase with Distorted Anion Lattice and Three Adjacent Long Channels

Abstract

γ-alumina, as a widely utilized material in human civilization for centuries, has been highly debated on its precise atomic structure. Herein we explore more than 10 million structures on (Al2O3)xH2O global potential energy surface from machine learning global optimization, and thus identify the most representative model for γ-alumina, namely the γ-AD model, which is a non-spinel phase featuring a highly distorted anion sublattice with connected voids forming three adjacent long channels. The γ-AD model is 57 meV/f.u. less stable than the θ-phase and at least 40 meV/f.u. more stable than all previously proposed models. Importantly, our γ-AD model reproduces correctly all minor structure patterns observed in the experiment, including the broadened small peaks below 33° in X-ray diffraction and the broadened double peak around 0.35 to 0.45 Å-1 in electron diffraction. The simulated surface pHPZC based on γ-AD model now agrees with the experimental data, suggesting the great promise for building the linkage between the γ-alumina atomic structure with its physiochemical properties from first principles.