CsY2M3Se5: The first quaternary chalcogenides of the A–Y–M–Q (A = Rb/Cs; M = Cu/Ag; Q = S/Se) system

Abstract

In this study, single crystals of two new quaternary chalcogenides, CsY2M3Se5 (M = Cu and Ag), have been prepared by the molten-flux method at 1273 K. Single-crystal X-ray diffraction studies established that both the compounds crystallize in the space group Cmcm of the orthorhombic crystal system and are isostructural. The title compounds, CsY2M3Se5 adopt the RbSm2Ag3Se5 structure type. The CsY2M3Se5 structure has seven crystallographically independent atomic sites (one Cs, one Y, two Cu/Ag, and three Se sites) that are fully occupied to form a three-dimensional (3D) tunnel-type structure. These valence-precise compounds are built up of the anionic framework of 3∞[Y2M3Se5]1−, where the Cs+ cations are present in the tunnels as space fillers. The Y atoms in both structures are octahedrally coordinated with six Se atoms, while Cu/Ag (M) atoms form a tetrahedral geometry. These distorted YSe6 octahedra share corners and edges with neighboring MSe4 tetrahedra to form 3D anionic networks. An optical absorption study shows the semiconducting nature of the CsY2Ag3Se5 in agreement with DFT studies of the title structures. The electronic structure and the theoretical thermoelectric properties of the CsY2Cu3Se5 and CsY2Ag3Se5 have also been calculated using the DFT method.