Revealing the electronic structure and optical properties of K6[Mo4O8F10] novel molybdenum oxyfluoride materials

Abstract

The electronic structure and optical properties of the molybdenum oxyfluoride K6[Mo4O8F10] single crystal were investigated. Based on X-ray diffraction data, the crystal structure was optimised so as to minimise the forces acting on each atom. The calculation reveal that K6[Mo4O8F10] is an indirect band gap semiconductor of about 1.51 eV, using the local density approximation, 1.72 eV, using gradient approximation (PBE-GGA), 1.81 eV using Engel–Vosko generalized gradient approximation and 2.01 eV, from the recently modified Becke–Johnson potential (TB-GGA-mBJ). Partial density of states reveals the orbitals’ contribution and the degree of the hybridisations between the orbitals. The contours of the valence electronic charge density of each atom in K6[Mo4O8F10] reveal that there are some electrons from Mo, K, F and O orbitals that are transferred to the valence bands and participate in the interactions between the Mo, K, F and O atoms to form covalent bonding. The strength of the covalent bond depends on the degree of the hybridisation and the electro-negativity differences between Mo, K, F and O atoms. The calculated bond lengths exhibit good agreement with the experimental data. The optical properties help to get deep insight into the electronic structure and reveal the types of the orbitals that participate in the optical transitions. It has been found that the investigated crystal possesses negative uniaxial anisotropy (δε = −0.102) and positive birefringence ( = 0.2765).