Electronic and Thermoelectric Properties of Transition Metal Substituted Tetrahedrites

A detailed theoretical and experimental study is carried out to understand the effect of transition metal atom (TM) substitution at the Cu tetrahedral site in synthetic tetrahedrite material Cu12–xTMxSb4S13 (TM = Mn, Fe, Co, Ni, and Zn). The samples are prepared by solid state synthesis method with the desired compositions. The X-ray diffraction (XRD) pattern of all the samples reveal tetrahedrite as the main phase with traces of secondary phases, confirmed by Electron Probe Micro Analysis (EPMA). X-ray Photoelectron Spectroscopy (XPS) reveals that TM is in +2 oxidation state for all samples except for Fe which shows a + 3 oxidation state. Ultraviolet Photoelectron Spectroscopy (UPS) measurements show the highest work function for Cu11.5Co0.5Sb4S13, indicating high band degeneracy. Density Functional Theory (DFT) calculations reveal that TM substitution introduces spin polarized states within the band structure, thus, changing the band degeneracy and density of states (DOS) at the Fermi level (EF). It is ...