New quaternary chalcogenide Ba4HgAs2S10 originating from the combination of linear [HgS2]2− and tetrahedral [AsS4]3− modules

Abstract

A new quaternary chalcogenide Ba₄HgAs₂S₁₀ has been successfully synthesized with the aid of a KI flux. The compound crystallizes in the space group C2/c (no. 9) of the monoclinic system [a = 22.7787(6) Å, b = 6.4712(2) Å, c = 25.0606(7) Å, β = 90.101(2)° and Z = 8]. It is the first example of tetrahedral [AsS₄]³⁻ and linear [HgS₂]²⁻ units coexisting in a single compound. The [AsS₄]³⁻ tetrahedra and [HgS₂]²⁻ units are totally separated by Ba²⁺. The UV-visible diffuse reflectance spectrum reveals a large bandgap of 2.98 eV for Ba₄HgAs₂S₁₀ and DSC measurement demonstrates the incongruent melting nature of the compound. Moreover, based on first-principles calculations, Ba₄HgAs₂S₁₀ is a direct bandgap semiconductor with the optical property related to the electron transition from the S-3p orbital to As-4p and Ba-5d orbitals.