Preparation, structures, and band gaps of RbInS2 and RbInSe2

The two compounds RbInS2 and RbInSe2 have been synthesized at 773K by means of the reactive flux method. These isostructural compounds crystallize in space group C2/c of the monoclinic system with 16 formula units in a cell at 153K of dimensions a=11.0653(7)A, b=11.0643(7)A, c=15.5796(9)A, and β=100.244(1)o for RbInS2, and a=11.477(3)A, b=11.471(3)A, c=16.186(6)A, and β=100.16(2)o for RbInSe2. The In atoms are four-coordinated. The structure consists of two-dimensional ∞2[InQ2-] (Q=S, Se) layers perpendicular to [001] separated from the Rb+ cations. Adamantane-like In4Q10 units are connected by common corners to form the layers. Band structure calculations indicate that these compounds are direct band-gap semiconductors with the smallest band gap at the Γ point. The calculated band gaps are 2.8eV for RbInS2 and 2.0eV for RbInSe2, values that are consistent with the colors of the compounds