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

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) angstrom, b = 6.4712(2) angstrom, c = 25.0606(7) angstrom, beta = 90.101(2)degrees 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.