Two new ternary chalcogenides Ba₂ZnQ₃ (Q = Se, Te) with chains of ZnQ₄ tetrahedra: Syntheses, crystal structure, and optical and electronic properties

Single crystals of Ba₂ZnQ₃ (Q = Se, Te) were obtained by solid-state reactions at 1173 K. These isostructural compounds crystallize in the K₂AgI₃ structure type. The Zn atoms in this structure are coordinated to four Q atoms (2 Q1, 1 Q2, 1 Q3) and these form a distorted tetrahedron around each Zn atom. Each ZnQ₄ tetrahedron shares two corners with neighboring ZnQ₄ tetrahedra resulting in the formation of infinite chains of [ZnQ₄^4-] units. The absorption spectrum of a single crystal of Ba₂ZnTe₃ shows an absorption edge at 2.10(2) eV, consistent with the darkred color of the crystals. From DFT calculations Ba₂ZnSe₃ and Ba₂ZnTe₃ are found to be semiconductors with electronic band gaps of 2.6 and 1.9 eV, respectively.