Structure And Thermoelectric Properties Of Cu-Sb-Se Ternary Chalcogenides

Cu-Sb-Se ternary chalcogenides have received a great attention in thermoelectrics recently,in that they have potential to be good thermoelectric materials due to their relatively high power factors and moderate thermal conductivities.In this work we focus on the investigations of the structures and thermoelectric properties of Cu-Sb-Se based chalcogenides involving solid solutions through different doping and composites via in-situ formed second phase CuSe.The detailed results are summarized below:?1?Synthesis of the ternary compound Cu₃SbSe₄ and then forming a solid solution with Cu₃SnS₄ and ZnSe.This strategy regulates the crystal structure of the solid solution?Cu₃SbSe₄?_1-x?Cu₃SnS₄?_x,and separates the contribution of the crystal structure distortion that plays an important role in enhancing the phonon scattering.This leads to the 22%reduction in lattice thermal conductivity at 607 K.At the same time,we also regulate the carrier concentration?n_H?and attain the optimal n_H value(¹0²⁰ cm^-3)at room temperature,which allows the maximum power factor?PF?to be increased to12.63?W-cm^-1K^-2,about two folds enhancement compared to the pristine Cu₃SbSe₄.As a consequence,the highest thermoelectric figure of merit?ZT?of the solid solution with a composition of?Cu₃SbSe₄?_0.9?Cu₃SnS₄?_0.1?ZnSe?_0.02 reaches the 0.65 at 700 K,which is 2.6 times that of the intrinsic Cu₃SbSe₄.This finding confirms that the co-doping of Cu₃SnS₄ and ZnSe in Cu₃SbSe₄ can effectively regulate the crystal structure and optimize the Hall carrier concentration?n_H?simultaneously,thereby improving the thermoelectric properties significantly.?2?We have also studied the thermoelectric properties of composites(Cu₃Sb_1-xSn_xSe₄)?CuSe?_y?x=0-0.04,y=0.3-0.08?with in-situ formed second phase CuSe and Sn incorporation into the Sb site.The results show that the composite(Cu₃Sb_1-xSn_xSe₄)?CuSe?_y can not only reduce the lattice thermal conductivity,but also increase the power factor.The highest thermoelectric figure of merit is 0.37,about 42%enhancement compared to the pristine Cu₃SbSe₄ for the composite(Cu₃Sb_0.98Sn_0.02Se₄)?CuSe?_0.11.This work reveals that the increased grain boundary and distorted crystal structure in the Cu₃SbSe₄ based composite are essential in improving the electrical conductivity,and at the same time reducing the lattice thermal conductivity.