Origin and effect of In–Sn ordering in InSnCo3S2: a neutron diffraction and DFT study

Abstract

The solid solution In_2−xSn_xCo₃S₂ is attractive due to a variety of interesting properties depending on the In/Sn content, i.e. half metal ferromagnetic Sn₂Co₃S₂, low dimensional metal In₂Co₃S₂, and semiconducting thermoelectric InSnCo₃S₂. For the latter, crystal structure effects and a metal to insulator transition are not only related to electron counting but also to ordering of In and Sn within and between Co Kagomé nets. These observations have not been adequately understood to date. The degree of ordering is now evaluated from neutron diffraction data to distinguish In and Sn. The origin and effects on crystal and electronic structures are studied by DFT calculations on a superstructure model. Relations of local bonding (electron localization function ELF and Bader's AIM theory), In/Sn site preference, crystal structure distortions, and the opening of the gap are explored. Results are generalised from predictions on isoelectronic compounds.