Role of the solvent medium in the wet-chemical synthesis of CuSbS2, Cu3SbS3, and bismuth substituted Cu3SbS3

Co-thermal decompositions of equimolar concentrations of thiourea complexes ([Cu(tu) 3 ]Cl and [Sb(tu) 2 ]Cl 3 ) in ethylene glycol and ethanolamine were attempted. Based on the results from powder X-ray diffraction, Raman spectroscopy, and energy dispersive spectral analysis of the products, Cu 3 SbS 3 in cubic symmetry emerged from ethylene glycol. In contrast, orthorhombic CuSbS 2 resulted from the ethanolamine medium. The generation of copper-rich and copper-poor sulfides was found to be the major reason behind the formation of these stoichiometries of the Cu-Sb-S system as verified by reacting the preformed Cu-S and Sb-S species in ethanolamine and ethylene glycol. Attempts to include bismuth (up to 50 mol%) for antimony were successful only in ethylene glycol medium. The inclusion of bismuth stabilized the orthorhombic form of Cu 3 SbS 3 , possibly due to the non-bonded lone pairs present on Bi 3+ and Sb 3+ -ions. The inclusion of bismuth confirmed from the successful refinement of powder X-ray diffraction pattern by the Rietveld method, Raman spectroscopy, and energy dispersive spectroscopy analysis. CuSbS 2 , Cu 3 SbS 3 (cubic) and Cu 3 Sb 0.50 Bi 0.50 S 3 showed broad absorption extending up to visible region in their UV-visible spectra. The bandgap values of 1.31, 1.40 and 0.94 eV were estimated by Tauc plots for Cu 3 SbS 3 , CuSbS 2 , and Cu 3 Sb 0.50 Bi 0.50 S 3 , respectively. Graphic abstract CuSbS 2 , Cu 3 SbS 3 (cubic) and Cu 3 Sb 0.50 Bi 0.50 S 3 showed broad absorption extending up to visible region in their UV-visible spectra. The bandgap values of 1.31, 1.40 and 0.94 eV were estimated by Tauc plots for Cu 3 SbS 3 , CuSbS 2 , and Cu 3 Sb 0.50 Bi 0.50 S 3 , respectively.