Ba3GeTeS4: A new quaternary heteroanionic chalcogenide semiconductor

We report the synthesis and characterization of a new quaternary heteroanionic chalcogenide phase, Ba3GeTeS4. A single-crystal X-ray diffraction study of a yellow-colored crystal of Ba3GeTeS4 shows that the compound is stoichiometric and crystallizes in the orthorhombic Cmcm space group having cell parameters of a = 6.8583(12) angstrom, b = 16.207(3) angstrom, c = 9.6239(19) angstrom, with four formula units (Z = 4) per unit cell. The unit cell of the structure consists of two Ba, one Ge, one Te, and two S sites. All the crystallographically independent atoms occupy special positions. The Ba3GeTeS4 structure is made up of zero-dimensional [GeS4](4)(-) anionic units along with Ba2+ cations, each of that is surrounded by the Te and S atoms. An optical UV-Vis absorption study on a polycrystalline sample of Ba3GeTeS4 establishes its semiconducting nature with a direct bandgap of 2.5(2) eV consistent with the yellow color of the sample. The polycrystalline Ba3GeTeS4 shows an extremely low value of thermal conductivity (similar to 0.46 W/mK) at 723 K. The ab-initio DFT calculations predict a high value of the thermoelectric figure of merit (zT > 1) for the hole doped-Ba3GeTeS4 sample. The crystal orbital Hamilton population (COHP) analysis shows that the Ge-S bonds are strongest in the structure, while the strengths of the Ba-S and Ba-Te interactions are similar.

Automated summary

We report the synthesis and characterization of a new quaternary heteroanionic chalcogenide phase, Ba3GeTeS4. The crystal structure consists of Ba, Ge, Te, and S atoms, and forms zero-dimensional [GeS4](4)(-) anionic units. The compound exhibits semiconducting nature with a direct bandgap of 2.5(2) eV and has a low thermal conductivity of around 0.46 W/mK at 723 K. Theoretical calculations suggest that the hole-doped Ba3GeTeS4 sample has a high thermoelectric figure of merit.