Preparation, Crystal Structure, Electronic Structure, Impedance Spectroscopy, and Raman Spectroscopy of Li₃SbS₃ and Li₃AsS₃

Li 3 SbS 3 was synthesized by solid‐state reaction of stoichiometric amounts of Li 2 S and Sb 2 S 3 in the ratio 3:1. The product is air and moisture sensitive. The crystal structure was determined from single crystals at room temperature. Pale grey Li 3 SbS 3 crystallizes in the orthorhombic space group Pna 2 1 (no. 33) with a = 7.9671(5) Å, b = 6.7883(5) Å, c = 10.0912(8) Å, V = 545.76(7) Å 3 , and Z = 4 (data at 20 °C). Antimony and sulfur atoms build isolated, trigonal pyramidal [SbS 3 ] 3– units, which are stacked along [100]. These [SbS 3 ] 3– units are connected by [LiS x ]‐polyhedra. The lithium ions have either a distorted tetrahedral coordination by sulfur in the case of Li2 and Li3 or a distorted square pyramidal environment in the case of Li1. The crystal structure is isotypic with Li 3 AsS 3 , which was obtained by reaction of stoichiometric amounts of lithium, arsenic, and sulfur in the ratio 3:1:3 in an excess of LiI. LiI serves only as a flux and is not incorporated in the crystal structure. Li 3 AsS 3 crystallizes as colorless rods, space group Pna 2 1 (no. 33) with a = 8.090(1) Å, b = 6.658(1) Å, c = 9.868(1) Å, V = 531.5(1) Å 3 , and Z = 4 (data at 20 °C). Both compounds are confirmed as semiconductors with bandgaps close to 3 eV from DFT‐calculations with GGA and hybrid functionals. Impedance spectroscopic measurements of Li 3 SbS 3 show a specific conductivity of σ = 1.6 × 10 –9 Ω –1 cm –1 at 323 K and of σ = 5.4 × 10 –5 Ω –1 cm –1 at 573 K. The activation energy is E A = 0.72 eV. Raman spectra of Li 3 SbS 3 are dominated by the stretching modes of the [SbS 3 ] 3– units at 333, 317, and 301 cm –1 at room temperature.