BaCu₂Se₂ based compounds as promising thermoelectric materials

In the past few years, many studies have been devoted to the thermoelectric properties of copper selenides and sulfides, and several families of materials have been developed with promising performances. In this paper, we report on the synthesis and thermoelectric properties of Na-doped BaCu₂Se₂ from 20 K to 773 K. By Na doping at the Ba site, the electrical conductivity can be increased by 2 orders of magnitude, and the power factor can reach 8.2 μW cm^-1 K^-2 at 773 K. Combined with a low thermal conductivity of 0.65 W m^-1 K^-1, a ZT of 1.0 has been obtained for Ba_0.925Na_0.075Cu₂Se₂ at 773 K, which is the highest value reported in this family to date. However, BaCu₂Se₂ volatilizes at 473 K, so a protective coating is necessary for its application. Besides, we studied the thermal expansion coefficient of BaCu₂Se₂ in this paper.