Tetrahedral Distortion and Thermoelectric Performance of the Ag-Substituted CuInTe₂ Chalcopyrite Compound

It is known that the electronic transport and heat conduction of thermoelectric materials are very sensitive to structural changes. In this article, the effect of Ag substitution on the crystal structure and hence thermoelectric properties of Cu1–xAgxInTe2 (x = 0, 0.05, 0.15, 0.25, 0.50, 0.75, and 1.00) solid solutions are investigated. The structural analysis shows that with the increasing Ag content, the lattice strain changes from tensile stress to compressive stress, and the tetrahedral distortion first relieves and then aggravates, which influences not only electronic but also thermal transport properties. The replacement of Cu by Ag results in the reduction of carrier concentration and lattice thermal conductivity. Although the enhancement in zT values of Cu1–xAgxInTe2 samples mainly originates from the significantly reduced lattice thermal conductivity, the improved electronic transport properties due to Ag substitution also play an important role. As a result, a maximum zT value of ∼1.36 is achieved for Cu0.75Ag0.25InTe2 at 823 K, which is a 92% improvement compared with the value of pristine CuInTe2. Our study provides a primary view of the relationship between the structure and thermoelectric performance, which is beneficial to the optimization of thermoelectric properties.