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) & Aring;, b = 3.7938(13) & Aring;, c = 11.604(4) & Aring;, beta = 106.095(10)degrees, 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)S-6, FeS6, and SbS5 units are the primary building blocks of the ScFeSb3S7 structure. Both resistivity and optical absorption [E-g = 1.5(1) eV] studies confirm that the ScFeSb3S7 is a semiconductor. A thermal conductivity (k(tot)) study shows that the polycrystalline sample is a poor thermal conductor with an ultralow k(tot) value of similar to 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.