BaCu₂SiS₄: A New Member of the A^IIB^I₂M^IVQ₄ Chalcogenide Family with a Chiral Crystal Structure

Abstract

Noncentrosymmetric ternary and quaternary chalcogenides are studied as promising nonlinear optical (NLO) materials in the mid‐infrared region. Here, we report the synthesis of a new material BaCu2SiS4 in the AIIBI2MIVQ4 family (A = divalent metal; B = monovalent metal; M = tetrel, Q = chalcogen), and discuss its crystal structure, thermal stability, optical behavior, and electronic structure. BaCu2SiS4 crystallizes in the noncentrosymmetric chiral space group P3221 with lattice parameters a = 6.1440(3) Å, c = 15.3542(8) Å, V = 501.95(6) Å3, Z = 3. The structure features helical channels formed by corner‐sharing [CuS4] and [SiS4] tetrahedral units. Synthesis was carried out in a molten salt flux, as opposed to a traditional solid‐state route from elements, to minimize the formation of a competing ternary phase, Ba2SiS4. BaCu2SiS4 is a semiconductor with an experimentally‐determined direct bandgap of ~2.2 eV. The material exhibits second harmonic generation (SHG) activity, confirming the noncentrosymmetric nature of the structure. Analysis of reported AIIBI2MIVQ4 crystal structures pointed out a correlation among potential structure types and the radii of the constituent elements. Total energy calculations were carried out to explore the relative stability of several reported crystal structures in this family of compounds..

ABa6Cu31Te22 (A = K, Rb, Cs) Featuring Polyanionic Copper–Telluride Frameworks with Ultralow Thermal Conductivity

“…Complex multinary chalcogenides demonstrate structural diversity by accommodating unique coordination requirements for specific metals. − Alkali, alkaline-earth, and transition metals generate a variety of metal–chalcogen polyhedral units that contribute to a diverse structural chemistry. − The same metal may exhibit different coordination environments in the crystal structure. For copper, a common polyhedral unit is a [Cu Q 4 ] ( Q = chalcogen) tetrahedron found in Ba 2 Cu 4 Te 5 , Ba 3 Cu 17 (Se,Te) 11 , and BaCu 2 SiS 4 . ,− [Cu Q 4 ] in combination with the [ AQ n ] ( A = alkali/alkaline-earth metal) polyhedral units can be combined in different ratios and connectivity modes often giving rise to new structure types. , Trigonal [Cu Q 3 ] units are also common in chalcogenides. An interesting example is the family of tetrahedrites, which has both tetrahedrally and trigonal planar coordinated Cu atoms. , Besides rich structural chemistry, multinary chalcogenides have useful applications in the fields of thermoelectricity, superconductivity, magnetism, nonlinear optics, and topological materials. ,, Among multinary chalcogenides, tellurides are different from lighter sulfides and selenides due to the lower electronegativity and higher radius of tellurium …”