LAUSR

Four new quaternary chalcogenides A2Ba7Sn4Q16 (A = Li, Na; Q = S, Se) were successfully synthesized in vacuum-sealed silica tubes for the first time. All of them crystallize in the noncentrosymmetric (NCS) cubic I3d space group with the cell parameters ranging from 14.807 to 15.4163 A and Z = 4, respectively. Interestingly, their isostructures are different from the structural transformations (from tetragonal to trigonal) appearing in previously reported Na2BaSnQ4 compounds. As observed in their structures, (Na/Ba)Q4 and SnQ4 units alternately connect with each other by sharing corners to build a three-dimensional (3D) framework structure with charge-balanced Ba cations located within tunnels, which is different from the observation that the Na atoms located inside the tunnels formed by the interconnection of the BaS8 and SnS4 units in Na2BaSnS4. Optical properties (diffuse-reflection, IR, and Raman spectra) were also systematically studied and the results indicate that their optical bandgaps are in the range from 1.75 to 2.5 eV. Moreover, the second harmonic generation (SHG) responses of the title compounds were also measured to be about 0.1–0.5 times higher than that of benchmark AgGaS2 under 2.09 μm radiation.