Syntheses, structures, optical properties, and electronic structures of KBaMSe3 (M = As, Sb)

The first two members in the quaternary A/A′/M/Q (A   =   alkali metal; A′   =   alkaline-earth metal; M   =   As, Sb, Bi; Q   =   S, Se, Te) system, namely the KBaMSe 3 (M   =   As, Sb) selenides, have been synthesized by solid state reactions. They are isostructural and crystallize in the centrosymmetric space group P 2 1 / c of the monoclinic system. In the structure, the trivalent M atom (M   =   As, Sb) is coordinated to three Se atoms forming a trigonal pyramid with the Se atoms serving as the triangle base, showing the stereochemical activity of the ns 2 lone pair electron. The MSe 3 (M   =   As, Sb) trigonal pyramids are totally isolated from each other with K + and Ba 2+ cations located between them. The optical band gaps of 2.26 (2)   eV for KBaAsSe 3 and 2.04 (2)   eV for KBaSbSe 3 , were deduced from the diffuse reflectance spectra. The first principles calculations were performed to study the electronic structures of KBaMSe 3 (M   =   As, Sb) compounds and the results indicated that these two compounds are indirect band gap semiconductors.