Preparation, crystal structure, electronic structure, impedance spectroscopy, and Raman spectroscopy of Li3SbS3 and Li3AsS3

Abstract

Li3SbS3 was synthesized by solid-state reaction of stoichiometric amounts of Li2S and Sb2S3 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 3SbS3 crystallizes in the orthorhombic space group Pna21 (no. 33) with a = 7.9671(5) Å, b = 6.7883(5) Å, c = 10.0912(8) Å, V = 545.76(7) Å3, 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 [LiSx]-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 Li3AsS3, 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. Li3AsS3 crystallizes as colorless rods, space group Pna21 (no. 33) with a = 8.090(1) Å, b = 6.658(1) Å, c = 9.868(1) Å, V = 531.5(1) Å3, 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 3SbS3 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 EA = 0.72 eV. Raman spectra of Li3SbS3 are dominated by the stretching modes of the [SbS3]3- units at 333, 317, and 301 cm-1 at room temperature. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.