Computer modeling of the local structure, mixing properties, and stability of binary oxide solid solutions with corundum structure

An original technique of computer modeling of substitutional solid solutions has been applied to Al₂O₃-Cr₂O₃, Al₂O₃-Fe₂O₃, and Fe₂O₃-Cr₂O₃ binary systems. The parameters of semiempirical interatomic potentials were optimized using the experimentally studied structural, elastic, and thermodynamic properties of pure components. Among point defects, the most energetically favorable ones for all three oxides are Schottky vacancy quintets. To model (M _x ¹ M _{1 ? x} ² )₂O₃ solid solutions, 4 × 4 × 1 disordered supercells with M ¹: M ² cation ratios of 1: 5, 1: 2, 1: 1, 2: 1, and 5: 1 have been constructed in the cation sublattice containing 192 atoms. The mixing enthalpy and volume, interaction parameters, bulk moduli, and vibrational entropy were found by minimizing the interatomic interaction energy in supercells with the symmetry P1. Calculations of the Gibbs energy made it possible to estimate the fields of stability of the Al₂O₃-Cr₂O₃ and Al₂O₃-Fe₂O₃ solid solutions; these estimates were compared with the experimental data. Histograms of M-M, M-O, and O-O interatomic distances were constructed and the local structure was analyzed for the Al_1.0Cr_1.0O₃, Al_1.0Fe_1.0O₃, and Fe_1.0Cr_1.0O₃ compositions.