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

Chem. Met. Alloys 13 (2020) 14-22

https://doi.org/10.30970/cma13.0400

I. Barchiy, O. Zubaka, E. Peresh, V. Sidey, O. Kokhan, I. Stercho, A. Fedorchuk, M. Piasecki

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.

Transition from the tetragonal structure of Rb₂TeI₆ to the monoclinic structure of K₂TeBr₆.

Keywords

Halide perovskite / Phase diagram / Crystal structure / Ab initio calculations / Electronic structure