Study on Enhancing the Thermoelectric Stability of the β-CuSe Phase by Mn Doping.

CuSe is a promising thermoelectric (TE) material due to its low cost, Earth abundance, and high thermoelectric properties. However, the biggest problem of CuSe is its unstable chemical properties. In particular, under the action of an electric field or gradient temperature field, the chemical potential of copper ions inside the material increases. When the external field is strong enough, the chemical potential of copper ions at the negative end of the material reaches the chemical potential of elemental copper. Under these conditions, copper ions must precipitate out, causing CuSe to be unstable, and making it unsuitable for use in applications. In this study, we prepared CuMnSe (x = 0, 0.02, 0.04 and 0.06) series bulk materials by vacuum melting-annealing and sintered by spark plasma sintering (SPS). We investigated the effects of Mn doping on the composition, microstructure, band structure, scattering mechanism, thermoelectric properties, and stability of CuSe. The results show that Mn doping can adjust the carrier concentration, promote the stabilization of the β-phase structure and improve the electrical properties of CuSe. When x = 0.06, the highest power factor () value of CuMnSe at 873 K was 1.62 mW m K. The results of carrier scattering mechanism analysis based on the conductivity ratio method show that the sample doped with Mn and pure CuSe had the characteristics of ionization impurity scattering, and the scattering factor was 3/2. However, the deterioration in thermal conductivity was large, and a superior value needs to be obtained. The cyclic test results of high-temperature thermoelectric properties show that Mn doping can hinder Cu migration and improve its thermoelectric stability, which preliminarily verifies the feasibility of using the stable zirconia mechanism to improve the thermoelectric stability of CuSe.