Predicting lattice parameter as a function of cation disorder in MgAl2O4 spinel

In the perfect magnesium aluminate spinel structure all the tetrahedral sites are occupied by Mg2+ ions, while Al3+ ions occupy all the octahedral sites. Real MgAl2O4, however, exhibits cation disorder (inversion), so that some Mg2+, ions reside in octahedral sites with an equal number of Al3+ ions in tetrahedral sites. Atomistic simulation was used to correlate the degree of inversion with changes in lattice parameter. Results from several approaches, including a combined energy minimization-Monte Carlo technique (CEMMC), are compared with available experimental data. These show that the mean field method is not useful, while the defect volume approach can yield predictions that are useful in interpreting the CEMMC results, which agree most closely with experiment.