Reciprocal K2TeI6 + Rb2TeBr6 and K2TeBr6 + Rb2TeI6 system: phase relations, crystal and electronic structures

Abstract

The stability of the K2TeBr6(I6) and Rb2ТеBr6(I6) compounds with perovskite structures was assessed within the idealized model of hard spheres (Goldschmidt’s rule). The possibility of formation of solid solutions along sections of the reciprocal system K2TeI6 + Rb2TeBr6 « K2TeBr6 + Rb2TeI6 was considered according to the quantitative criteria of Vozdvyzhensky. The K2TeBr6–Rb2TeI6 system was investigated by DTA and X-ray diffraction and the phase diagram was constructed. The binary system is of the invariant eutectic type and characterized by the formation of limited solid solutions. On the basis of crystallographic data the bonds lengths in the crystal structures were compared with the covalent and ionic radii of the atoms. The results showed that the chemical bonds in the K2TeBr6(I6) and Rb2ТеBr6(I6) ternary compounds are of the mixed (combined) type – iono-covalent with a larger ionic component. The electronic structures of the K2(Rb2)TeBr6(I6) compounds were calculated by the ab initio quantum-mechanical DFT method.