KBiMS 4 ( M=Si, Ge): Synthesis, structure, and electronic structure

Abstract

Two new bismuth sulfides KBiSiS 4 and KBiGeS 4 have been synthesized by means of the reactive flux method. They adopt the RbBiSiS 4 structure type and crystallize in space group P2 1/ c of the monoclinic system. The structure consists of [ Bi M S 4 − ] 2 ∞ ( M=Si, Ge) layers separated by bicapped trigonal-prismatically coordinated K atoms. The M atom is tetrahedrally coordinated to four S atoms and the Bi atom is coordinated to a distorted monocapped trigonal prism of seven S atoms. The optical band gap of 2.25(2) eV for KBiSiS 4 was deduced from the diffuse reflectance spectrum. From a band structure calculation, the optical absorption for KBiSiS 4 originates from the [ BiSiS 4 − ] 2 ∞ layer. The Si 3 p orbitals, Bi 6 p orbitals, and S 3 p orbitals are highly hybridized near the Fermi level. The orbitals of K have no contributions on both the upper of valence band and the bottom of conduction band.