Syntheses, structures, optical properties, and electronic structures of Ba ₆ Cu ₂ GSn ₄ S ₁₆ (G = Fe, Ni) and Sr ₆ D ₂ FeSn ₄ S ₁₆ (D = Cu, Ag)

Ba ₆ Cu ₂ GSn ₄ S ₁₆ (G = Fe, Ni), and Sr ₆ D ₂ FeSn ₄ S ₁₆ (D = Cu, Ag) were synthesized in an A-B-P-Q (A = Sr, Ba; B = Cu, Ag, Li; P = Sn, Ge; Q = S, Se, Te) system, through the introduction of the Fe and Ni atoms. The four compounds were found to be isostructural. They crystallize in space group I4̅3d (no. 220) of the three-dimensional cubic structure. The structure is composed of SnS ₄ and (Cu|G)S ₄ by sharing corners with Ba ²⁺ cations distributed in the channels of the Ba ₆ Cu ₂ GSn ₄ S ₁₆ (G = Fe, Ni). The structure is composed of SnS ₄ and (D|Fe)S ₄ by sharing corners with Sr ²⁺ cations distributed in the channels of the Sr ₆ D ₂ FeSn ₄ S ₁₆ (D = Cu _, Ag). The UV–vis diffuse reflectance spectra showed the Ba ₆ Cu ₂ FeSn ₄ S ₁₆ , Ba ₆ Cu ₂ NiSn ₄ S ₁₆ , Sr ₆ Cu ₂ FeSn ₄ S ₁₆ , and Sr ₆ Ag ₂ FeSn ₄ S ₁₆ energy band gaps to be 1.20 eV, 0.82 eV, 1.53 eV and 1.87 eV, respectively.