Towards band gap engineering in skutterudites: The role of X4 rings geometry in CoSb3-RhSb3 system

Strong relationship between direct X-X bonds and electronic properties in many thermoelectric materials is observed. In present work investigation on the relation between properties of such bonds in skutterudite-structured compounds and band gap size was performed. Various compositions of Co1-xRhxSb3 (x = 0 to 1) solid solutions were studied theoretically, using experimental structure data found in a literature as well as structures optimized through ab initio methods. Electronic structure of a set of pure CoSb3/RhSb3 structures subjected to various external pressure conditions as well as solid solutions was obtained within DFT calculations using WIEN2k package. Topological properties of total electron density were determined under Bader's QTAiM formalism. Importance of charge transfer changes between Co/Rh and Sb atoms and their relation to the band structure were highlighted. According to presented results, strong influence of longer Sb-Sb bonds of Sb4 ring on the band structure was explained, suggesting possible ways of CoSb3-RhSb3 band gap engineering.