Somnath Acharya1,Junphil Hwang2,Kwangrae Kim1,Woohyun Hwang1,Aloysius Soon1,Woochul Kim1
Yonsei University1,Ewha Womans University2
Somnath Acharya1,Junphil Hwang2,Kwangrae Kim1,Woohyun Hwang1,Aloysius Soon1,Woochul Kim1
Yonsei University1,Ewha Womans University2
Currently, high-entropy alloys are of great interest in material science and engineering research. Unlike conventional alloys, which consist of two or three elements, high-entropy alloys contain multiple principal elements to form a single-phase solid solution with stable crystal structures. Because of its high configuration entropy, high-entropy materials can be more stable at elevated temperatures due to the minimization of Gibbs free energy (<i>G = H - TS,</i> where <i>H</i> is enthalpy, <i>S</i> is entropy, and <i>T</i> is temperature). In the context of thermoelectric material, the performance can be greatly improved by optimizing the entropy through lattice thermal conductivity suppression and via improving the crystal structure symmetry resulting in large Seebeck coefficients. Chalcopyrite compounds [(Cu/Ag)(In/Ga)Te<sub>2</sub>] have been considered a promising thermoelectric material with high Seebeck coefficients and decent electrical conductivity. Here, we have studied CuGaTe<sub>2</sub>-based multicomponent chalcopyrite to investigate their thermal and electrical transport properties. The major drawback of the CuGaTe<sub>2</sub>-based compound is high lattice thermal conductivity due to its diamondoid structure. In this study, we observe that Ag and In alloying in Cu<sub>1-x</sub>Ag<sub>y</sub>Ga<sub>0.8</sub>In<sub>0.2</sub>Te<sub>2 </sub>leads to the enhancement of power factor and significantly reduces the lattice thermal conductivity. The transport studies and DFT calculation suggest that the power factor enhancement can be justified by the increase of charge carriers while the low lattice thermal conductivity has been explained through a strong phonon coupling between low-frequency optical phonons and heat-carrying acoustic phonons. Additionally, manipulating the configuration entropy via introducing Zn in Cu<sub>1-x</sub>Ag<sub>y</sub>Ga<sub>0.8</sub>In<sub>0.2</sub>Te<sub>2</sub>, lowers further lattice thermal conductivity to ~ 0.38 W/m-K at 850 K due to the strengthening of phonon scattering. Therefore, entropy engineering leads to significance improved thermoelectric performance of CuGaTe<sub>2</sub>-based material.