ScFeSb3S7: Synthesis and characterization of a new mixed-metal sulfide

Mixed transition metal chalcogenides are pursued for various semiconducting applications. Herein, we report a new mixed transition metal containing quaternary chalcogenide, ScFeSb3S7, which has been prepared by a high-temperature reaction of elements at 1173 K. A single-crystal X-ray diffraction study shows that the monoclinic ScFeSb3S7 structure (space group: C2/m) is disordered with a mixed Sc and Sb site. The lattice parameters of the structure are a = 12.439(5) Å, b = 3.7938(13) Å, c = 11.604(4) Å, β = 106.095(10)°, and Z = 2. The seven unique crystallographic sites of the structure are occupied, which include Fe1, Sb1, mixed Sc1/Sb2, and four S sites. Each of the Fe1 and Sc1/Sb2 atoms is coordinated with six neighboring sulfur atoms in an octahedral fashion, whereas the Sb1 atom occupies the center of a distorted square pyramidal geometry of the S atoms. The (Sc1/Sb2)S6, FeS6, and SbS5 units are the primary building blocks of the ScFeSb3S7 structure. Both resistivity and optical absorption [Eg = 1.5(1) eV] studies confirm that the ScFeSb3S7 is a semiconductor. A thermal conductivity (ktot) study shows that the polycrystalline sample is a poor thermal conductor with an ultralow ktot value of ∼0.30 W/mK at 773 K. DFT studies also indicate the semiconducting nature of the ScFeSb3S7. The COHP analyses suggest stronger bonding interactions between Sb and S than the Sc/Fe with the S atoms. [Display omitted] •Single crystals of a new quaternary ScFeSb3S7 have been synthesized.•The structure comprises of (Sc1/Sb2)S6, FeS6, and SbS5 units as the primary building blocks.•The semiconducting ScFeSb3S7 sample shows an optical bandgap of 1.5(1) eV.•An ultralow thermal conductivity (ktot) value of ∼0.30 W/mK at 773 K is also observed for the ScFeSb3S7 sample.•Theoretical bonding analyses show polar covalent interactions between metals and S atoms.