Electronic structure of normal, inverse, and partially inverse spinels in the MgAl2O4 system.

Abstract

The electronic structure of normal, inverse, and partially inverse spinels in the ${\mathrm{MgAl}}_{2}$${\mathrm{O}}_{4}$ system are studied by means of first-principles calculations. For the normal spinel, the calculated ground-state properties are in good agreement with experimental data. A local-density-approximation band gap of 5.80 eV is obtained. For the inverse and partially inverse spinels, in which up to eight Mg atoms in a tetrahedral coordination are interchanged with eight of the 16 Al atoms in octahedral coordination, the atomic positions are relaxed by realistic interatomic pair potentials. Based on the relaxed models, the electronic structure and their dependence on the inversion parameter \ensuremath{\lambda} are studied. The total lattice energy increases as \ensuremath{\lambda} increases with a change of slope at \ensuremath{\lambda}=4/16. It is found that the general features in the density of states (DOS) in these spinels are quite similar with subtle differences in the peak structures between normal and inverse spinels. The smallest band gap of 4.84 eV is found at \ensuremath{\lambda}=4/16. The orbital decomposition of the partial DOS of Al and Mg in different coordination environments is fully analyzed. These results are discussed in the context of an order-disorder phenomenon associated with a cation site interchange, and their implications on spectroscopic detections. \textcopyright{} 1996 The American Physical Society.