Unraveling the Role of Entropy in Thermoelectrics: Entropy-Stabilized Quintuple Rock Salt PbGeSnCd<sub><i>x</i></sub>Te<sub>3+<i>x</i></sub>
Yukun Liu, Hongyao Xie, Zhi Li, Yinying Zhang, Christos D. Malliakas, Muath Al Malki, Stephanie M. Ribet, Shiqiang Hao, Thang Duc Pham, Yuankang Wang, Xiaobing Hu, Roberto dos Reis, G. Jeffrey Snyder, Ctirad Uher, Christopher Wolverton, Mercouri G. Kanatzidis, Vinayak P. Dravid
Abstract
Entropy-engineered materials are garnering considerable attention owing to their excellent mechanical and transport properties, such as their high thermoelectric performance. However, understanding the effect of entropy on thermoelectrics remains a challenge. In this study, we used the PbGeSnCd x Te 3+ x family as a model system to systematically investigate the impact of entropy engineering on its crystal structure, microstructure evolution, and transport behavior. We observed that PbGeSnTe 3 crystallizes in a rhombohedral structure at room temperature with complex domain structures and transforms into a high-temperature cubic structure at ∼373 K. By alloying CdTe with PbGeSnTe 3, the increased configurational entropy lowers the phase-transition temperature and stabilizes PbGeSnCd x Te 3+ x in the cubic structure at room temperature, and the domain structures vanish accordingly. The high-entropy effect results in increased atomic disorder and consequently a low lattice thermal conductivity of 0.76 W m –1 K –1 in the material owing to enhanced phonon scattering. Notably, the increased crystal symmetry is conducive to band convergence, which results in a high-power factor of 22.4 μW cm –1 K –1 . As a collective consequence of these factors, a maximum ZT of 1.63 at 875 K and an average ZT of 1.02 in the temperature range of 300–875 K were obtained for PbGeSnCd 0.08 Te 3.08 . This study highlights that the high-entropy effect can induce a complex microstructure and band structure evolution in materials, which offers a new route for the search for high-performance thermoelectrics in entropy-engineered materials.