La12Sb9S38: a new semiconducting lanthanum antimony polysulfide with a mixed La/Sb site

With the discovery of La12+xSb9-yS38-z, for simplicity called La12Sb9S38, we characterized the first lanthanum antimony polysulfide. Despite La/Sb mixed occupancies and S atom deficiencies, this material exhibits only a small phase width, as evident from our two single crystal structure studies. The refined formulae of La12.17(1)Sb8.59(2)S37.86(3) and La12.10(1)Sb8.60(2)S37.79(6) are almost equivalent, despite significantly different starting compositions. La12.17(1)Sb8.59(2)S37.86(3) crystallizes in a new structure type, space group Pm3, with Z = 1 and a = 11.1455(2) angstrom (La12.10(1)Sb8.60(2)S37.79(6): a = 11.151(1) angstrom). This new structure type is composed of a complex three-dimensional network of different Sb-S polyhedra and disordered S-2(2-) dumbbells. The material is a red semiconductor with an optical band gap of 1.75 eV. Despite its large sulfur content of 65 atomic-% and a therefore relatively low average molar mass of 67.4 g mol(-1), the material exhibits low thermal conductivity values between 0.80 W m(-1) K-1 and 1.05 W m(-1) K-1 as a consequence of its complex crystal structure and various disorders.

Automated summary

La12Sb9S38 is the first lanthanum antimony polysulfide characterized, demonstrating red semiconductor properties and low thermal conductivity values, attributed to its complex crystal structure containing different Sb-S polyhedra and disordered S-2(2-) dumbbells.