Scalable synthesis of Cu–Sb–S phases from reactive melts of metal xanthates and effect of cationic manipulation on structural and optical properties

We report a simple, economical and low temperature route for phase-pure synthesis of two distinct phases of Cu–Sb–S, chalcostibite (CuSbS(2)) and tetrahedrite (Cu(12)Sb(4)S(13)) nanostructures. Both compounds were prepared by the decomposition of a mixture of bis(O-ethylxanthato)copper(II) and tris(O-ethylxanthato)antimony(III), without the use of solvent or capping ligands. By tuning the molar ratio of copper and antimony xanthates, single-phases of either chalcostibite or tetrahedrite were obtained. The tetrahedrite phase exists in a cubic structure, where the Cu and Sb atoms are present in different coordination environments, and tuning of band gap energy was investigated by the incorporation of multivalent cationic dopants, i.e. by the formation of Zn-doped tetrahedrites Cu(12−x)Zn(x)Sb(4)S(13) (x = 0.25, 0.5, 0.75, 1, 1.2 and 1.5) and the Bi-doped tetrahedrites Cu(12)Sb(4−x)Bi(x)S(13) (x = 0.08, 0.15, 0.25, 0.32, 0.4 and 0.5). Powder X-ray diffraction (p-XRD) confirms single-phase of cubic tetrahedrite structures for both of the doped series. The only exception was for Cu(12)Sb(4−x)Bi(x)S(13) with x = 0.5, which showed a secondary phase, implying that this value is above the solubility limit of Bi in Cu(12)Sb(4)S(13) (12%). A linear increase in the lattice parameter a in both Zn- and Bi-doped tetrahedrite samples was observed with increasing dopant concentration. The estimated elemental compositions from EDX data are in line with the stoichiometric ratio expected for the compounds formed. The morphologies of samples were investigated using SEM and TEM, revealing the formation of smaller particle sizes upon incorporation of Zn. Incorporation of Zn or Bi into Cu(12)Sb(4)S(13) led to an increase in band gap energy. The estimated band gap energies of Cu(12−x)Zn(x)Sb(4)S(13) films ranges from 1.49 to 1.6 eV, while the band gaps of Cu(12)Sb(4−x)Bi(x)S(13) films increases from 1.49 to 1.72 eV with increasing x.