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 KBaMSe₃ (M = As, Sb) selenides, have been synthesized by solid state reactions. They are isostructural and crystallize in the centrosymmetric space group P2₁/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 ns² lone pair electron. The MSe₃ (M = As, Sb) trigonal pyramids are totally isolated from each other with K⁺ and Ba²⁺ cations located between them. The optical band gaps of 2.26 (2) eV for KBaAsSe₃and 2.04 (2) eV for KBaSbSe₃, were deduced from the diffuse reflectance spectra. The first principles calculations were performed to study the electronic structures of KBaMSe₃ (M = As, Sb) compounds and the results indicated that these two compounds are indirect band gap semiconductors.

Journal of Alloys and Compounds,  2014

The metal atom coordination geometry in KBaAsSe₃

Unit cell of the KBaAsSe3 structure