Synthesis, structure, and electronic structure of CsAgGa2Se4

The new metal chalcogenide CsAgGa2Se4 has been synthesized by means of the reactive flux method. It crystallizes in the space group P21/c of the monoclinic system with cell dimensions of a=11.225(2) Å, b=7.9443(16) Å, c=21.303(4) Å, β=103.10(3), V=1850.3(6), and Z=8. The structure contains two-dimensional ∞2[AgGa2Se4]− layers separated by Cs+ cations. The ∞2[AgGa2Se4]− superlayer possesses a novel chain–sublayer–chain structure: a ∞2[Ag2GaSe6]7− sublayer, composed of ∞1[AgGaSe4]4− chains that are further connected by Ag+ ions, is sandwiched by parallel ∞1[Ga3Se8]7− chains to generate the ∞2[AgGa2Se4]− superlayer. From a band structure calculation, the orbitals of all atoms have contributions to the bottoms of conduction bands, but the band gap is mainly determined by the 4s, 4p orbitals of Ga and Se.