Synthesis, characterization and theoretical investigation of a new chalcohalide, Ba4GaS4F3

A new fluorine-containing chalcohalide, Ba4GaS4F3, has been synthesized by conventional high-temperature solid-state reaction. The compound crystallizes in the centrosymmetric space group I41/a with a = b = 16.628 (5) Å, c = 17.139 (10) Å, Z = 16. Experimental and theoretical results confirm that Ba4GaS4F3 is a direct band gap compound with an experimental band gap of about 3.13 eV, and the band gap is mainly determined by the Ba-5p, F-2p and S-3p orbitals. What's more, different from the many newly discovered chalcohalides in the Ba3AM4Q (A = Ga, In; M = S, Se; Q = Cl, Br, I) family, Ba4GaS4F3 is the first reported compound in the Ba4AM4D3 (A = Ga, In; M = chalcogen; D = halogen) family. The results enrich the structural diversity of metal chalcohalides.

Experimental and theoretical studies of the ternary thiophosphate PbPS3 featuring ethane-like [P2S6]4- units

The ternary thiophosphate PbPS₃ was synthesized by a high-temperature solid-state reaction using PbS, P and S. Single-crystal X-ray diffraction analysis reveals that the compound crystallizes in the P2₁/c space group. It features a three-dimensional structure, which consists of [PbS₈] hendecahedra and isolated ethane-like [P₂S₆]^4- units. PbPS₃ can be easily obtained by different methods and shows high air stability, which is beneficial to its chemical synthesis and large-sized crystal growth. The crystal structure, optical properties and electronic structure of PbPS₃ have been researched by experimental methods and first-principles calculations. The results show that PbPS₃ has a moderate bandgap (E_{g. exp.} = 2.60 eV) and birefringence (Δn_cal. = 0.094@1064 nm), as well as a wide transparent range. Furthermore, to better understand the origin of the birefringence, structure comparisons and theoretical calculations were carried out. With a relatively high physicochemical stability and easy synthesis, PbPS₃ can be expected to be a prospective birefringent material.