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

Abstract

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 Cu 1−x Ag x InTe 2 (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 Cu 1−x Ag x InTe 2 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 Cu 0.75 Ag 0.25 InTe 2 at 823 K, which is a 92% improvement compared with the value of pristine CuInTe 2 . Our study provides a primary view of the relationship between the structure and thermoelectric performance, which is beneficial to the optimization of thermoelectric properties.

Significant Improvement in Thermoelectric Performance of AgInSe2-Based Composites through In Situ Formation of Ag2Se

“…These results suggest the good thermal stability of the material. A small change in TE performance after a cycling test might be related to the defects existing in the samples because the defects have a significant impact on the TE properties of diamond-like semiconductors …”

“…A small change in TE performance after a cycling test might be related to the defects existing in the samples because the defects have a significant impact on the TE properties of diamond-like semiconductors. 49 The improvement in TE performance is, on one hand, due to the contribution of the Ag 2 Se species that enhances the n H value, which leads the highest PF to increase from 1.68 μW cm −1 K −2 (x = 0) to 2.48 μ W cm −1 K −2 (x = 0.3) (see Figure S5). On the other hand, it is attributed to the increased phonon scattering on the distorted lattice structure at high temperatures.…”

Recent advances in designing thermoelectric materials

“…This has been particularly useful for diamond-like chalcopyrite structures with tetragonal symmetry, where manipulating the tetragonal distortion parameter (c/2a) towards unity minimizes the energy splitting between the degenerate valence bands. [322][323][324] A unity tetragonal distortion parameter essentially indicates a pseudocubic symmetry in the tetragonal structures. Additionally, the enhanced symmetry with various substitutions leads to multiple degenerate carrier pockets in the conduction band, thereby providing an opportunity to tune the transport properties of both the charge carriers.…”

Unraveling the role of chemical composition in the lattice thermal conductivity of oxychalcogenides as thermoelectric materials

“…60 Moreover, the substitution of Ag by Cu favors the presence of carriers, which is benecial to obtaining higher power factors. 61,62 Although the calculation of ZT is out of the scope of this work, it is possible to anticipate that BiOAg 0.5 Cu 0.5 Se is a potential candidate as thermoelectric material.…”