Syntheses of five new layered quaternary chalcogenides SrScCuSe3, SrScCuTe3, BaScCuSe3, BaScCuTe3, and BaScAgTe3: crystal structures, thermoelectric properties, and electronic structures

Abstract

Copper/silver-containing chalcogenides have recently attracted significant interest for their promising thermoelectric applications. In this article, we report the syntheses of five new layered quaternary Cu/Ag-containing chalcogenides: SrScCuSe₃, SrScCuTe₃, BaScCuSe₃, BaScCuTe₃, and BaScAgTe₃. The single-crystal X-ray diffraction studies show that all the Cu-containing compounds are isostructural and crystallize in the orthorhombic crystal system in the Cmcm space group. Interestingly, the crystal structure of isoelectronic BaScAgTe₃ does not adopt the same structure type as observed for AkScCuQ₃ (Ak = Sr/Ba; Q = Se/Te). Instead, it crystallizes in the primitive orthorhombic Pnma space group. The crystal structures of all these compounds are two-dimensional consisting of ²_∞[ScMQ₃]²⁻ layers (M = Cu/Ag) separated by Ak²⁺ cations. The building blocks of these structures are distorted tetrahedral MQ₄ and octahedral ScQ₆ units. The arrangement and sharing of the MQ₄ and ScQ₆ units are slightly different for the two structure types, AkScCuQ₃ (Ak = Sr and Ba; Q = Se and Te) and BaScAgTe₃. Resistivity study confirms the metallic behavior for BaScCuTe₃. The positive sign of thermopower values suggests holes as the charge carriers. The value of the thermoelectric figure of merit (zT) for polycrystalline BaScCuTe₃ was found to be enhanced on increasing the temperature with a maximum zT value of 0.34 at 779 K. In addition, we have also studied the structural and electronic properties of BaScCuTe₃ and BaScAgTe₃ within the framework of density functional theory (DFT).