Crystal and Electronic Structures of Alluaudite-Type Double Molybdates of Scandium and Indium

Abstract

Double molybdates of indium and scandium with alluaudite structure are prepared by the solid-phase synthesis method. The crystal structure of the indium containing compound is refined and optical characteristics of Na₅R(Mo0₄)₄(R = Sc, In) are determined. Electronic structures of Na₅R(Mo0₄)₄(R = Sc, In) molybdates are studied within the ab initio method taking account of Na/Sc(In) positional disordering. Calculations of the imaginary part of dielectric function predict the optical gap of ~3.8 eV, in accordance with absorption spectroscopy data. It is established that formation energy of sodium vacancies strongly depends on sodium position and Sc(In) concentration. As a result, various diffusion mechanisms may be activated in alluaudite-type compounds with high and low contents of metal R.