Ba2In2Q5 (Q = S, Se): Synthesis, Crystal Structures, Electronic Structures, and Optical Properties

Two ternary metal chalcogenides, Ba(2)In(2)Q(5) (Q = S, Se) were successfully synthesized by solid-state reactions. They are isostructural and crystallize in the orthorhombic space group Pbca (no. 61). Both of them have a similar three-dimensional (3D) framework structure, which is composed of [InQ(4)] (Q = S, Se) tetrahedra that are alternatingly connected on layer in the ab plane, with Ba2+ cations arranged between In-S or In-Se layers for electric charge balance. The measured Raman and IR spectra show that title compounds have broad transparency range up to 20 m. From the UV/Vis/NIR diffuse reflectance spectra, it can be seen that the bandgaps of Ba2In2S5 and Ba2In2S5 are 2.47 eV and 2.12 eV, which are larger than these of the calculation values (Ba2In2S5, 2.362 eV and Ba2In2Se5, 1.908 eV), respectively. The calculated partial densities of states indicate that the bandgaps are determined by the interaction of S-3p and In-5s (Ba2In2S5) or Se-4p and In-5s (Ba2In2Se5), respectively. The calculated birefringences (n) are about 0.03 (Ba2In2S5) and 0.05 (Ba2In2Se5) as the wavelength above 1 m, respectively.