Optimization of thermoelectric transport performance of nickel-doped CuGaTe<sub>2</sub>

Abstract

Thermoelectric material is a new type of functional material that can realize the direct conversion between heat energy and electric energy. It has received a lot of attention because it has wide practical applications. However, the applications of thermoelectric devices are limited by their low conversion efficiencies. The conversion efficiency is determined mainly by the thermoelectric properties of the material. In this work, a compound of CuGaTe<sub>2</sub> chalcopyrite is selected as a research object, and a series of Ni-doped samples Cu<sub>1–<i>x</i></sub>Ni<i><sub>x</sub></i>GaTe<sub>2</sub> (<i>x </i>= 0–0.75%) is synthesized by the vacuum melting method. The temperature dependent thermal and electrical properties for Cu<sub>1–<i>x</i></sub>Ni<i><sub>x</sub></i>GaTe<sub>2</sub> (<i>x</i> = 0–0.75%) compounds are investigated. The results show that the Ni atom can effectively replace the Cu atom of the material, and thus leading the carrier concentration to decrease slightly and inducing the mobility to increase. At the same time, the Seebeck coefficient increases significantly after Ni doping: on the one hand, the increase is due to the decrease of the carrier concentration of the sample; on the other hand, the effective increase of the density of states near the Fermi level plays an important role in increasing Seebeck coefficient. Then, the thermal conductivity decreases effectively due to the enhancement of point defect scattering caused by Ni doping, and the minimum lattice thermal conductivity is reduced by ~30% in comparison with the matrix lattice thermal conductivity. Finally, the maximum <i>ZT</i> value for Cu<sub>0.095</sub>Ni<sub>0.005</sub>GaTe<sub>2</sub> sample (<i>ZT</i> = 1.26 at 873 K) is obtained to be ~56% larger than that for CuGaTe<sub>2</sub>. This work indicates that the doping magnetic element Ni at Cu site is also one of the effective ways to improve the thermoelectric properties of CuGaTe<sub>2</sub> materials.