Synthesis, Crystal Structures, Optical Properties and Theoretical Calculations of Two Metal Chalcogenides Ba2AlSbS5 and Ba2GaBiSe5

Two quaternary metal chalcogenides, Ba2AlSbS5and Ba2GaBiSe5, were successfully synthesized by solid-state reaction in sealed silica tubes. Both of them crystallize in the same orthorhombic space groupPnma, but they appear with obviously different construction features. For example, Ba2AlSbS5exhibits [SbS3]3−units and zero-dimensional (0D) [AlSbS5]4−clusters, which is different from those ([BiSe6]3−units and 1D∞[GaBiSe5]4−chains) of Ba2GaBiSe5. We also systematically investigated the entire series of Ba2MIIIMIII’Q5(MIII= Al, Ga, In; MIII’ = As, Sb, Bi; Q = S, Se, Te) compounds, and the results showed that the interconnection of MIIIQ4and MIII’Qn(n= 3, 5, 6) units can form three different structural types, including 0D [MIIIMIII’Q5] clusters, single [MIII’Q3] chains and isolated [MIIIQ4] units, or [MIIIQ3]nand [MIII’Q3]ndouble chains, which may be induced by the flexible coordination and on-link modes of MIII’ atoms. Spectral investigation shows that their bandgaps are about 2.57 eV for Ba2AlSbS5and 2.14 eV for Ba2GaBiSe5. Theoretical calculation was also used to analyze their structure-property relationships, and the results indicate that the title compounds exhibit larger birefringences (Δn> 0.10), thus having potential as the IR birefringent materials.