[Ba4X][In19S32] (X = Cl, Br): two quaternary metal chalcohalides exhibiting remarkable photocurrent responses

Abstract

Inorganic metal chalcohalides, as significant semiconductor materials, have emerged as promising candidates for photoelectric applications. Herein, a new type of quaternary chalcohalide, [Ba₄X][In₁₉S₃₂] (X = Cl, Br), has been discovered using the high-temperature halide salt flux method. Single-crystal X-ray diffraction analysis reveals that they are isostructural and crystallize in the tetragonal space group I4₁/amd (no. 141) featuring the octahedral hole formed by six [InS₄]⁵⁻ tetrahedra filled with a [ClBa₄]⁷⁺ polycation, surrounded by a three-dimensional covalent framework formed by interconnecting [InS₆]⁹⁻ octahedra through corner-sharing and edge-sharing. Moreover, [Ba₄Cl][In₁₉S₃₂] and [Ba₄Br][In₁₉S₃₂] exhibit wide optical bandgaps of 2.70 eV and 2.46 eV, respectively, and moderate birefringences (0.044 @ 2100 nm and 0.042 @ 2100 nm, respectively). Specifically, [Ba₄X][In₁₉S₃₂] (X = Cl, Br) display remarkable photocurrent responses under simulated solar-light illumination, implying their potential for photocatalytic applications. Theoretical calculations were employed to understand the interrelationship between the optical properties and electronic structure. The study on the synthesis and structure–property relationship analysis of inorganic metal chalcohalides provides new insight into the exploration of promising photoelectric materials.