Electronic and optical properties of theMg2−xFexSiO4spinel: From band insulator to Mott insulator

Abstract

The crystal properties and electronic structure of Mg2−xFexSiO4 spinel have been studied using the densityfunctional theory including the local Hubbard interaction U within the generalized gradient approximation. The lattice constant depends linearly on increasing iron concentration x in agreement with the Vegard’s law. The contributions of the Fe t2g and Fe eg orbitals to the electronic density of states have been determined and their crucial role in the band-gap formation has been elucidated. We explain the decrease in the insulating gap with increasing iron concentration on the basis of the Mott-Hubbard picture of correlated insulators. Thus, it was revealed that the electronic structure of Mg2−xFexSiO4 evolves from the band insulator found in Mg2SiO4 to the Mott insulator with increasing iron concentration. We present also the absorption spectra derived from the complex dielectric tensor, which are in good qualitative agreement with the previously reported experimental data for a wide range of energies.