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.