High thermoelectric performance enabled by convergence of nested conduction bands in Pb7Bi4Se13 with low thermal conductivity
Lei Hu, Yue‐Wen Fang, Feiyu Qin, Xun Cao, Xiaoxu Zhao, Yubo Luo, D. V. Maheswar Repaka, Wenbo Luo, Ady Suwardi, Thomas Soldi, Umut Aydemir, Yizhong Huang, Zheng Liu, Kedar Hippalgaonkar, G. Jeffrey Snyder, Jianwei Xu, Qingyu Yan
Abstract
Abstract Thermoelectrics enable waste heat recovery, holding promises in relieving energy and environmental crisis. Lillianite materials have been long-term ignored due to low thermoelectric efficiency. Herein we report the discovery of superior thermoelectric performance in Pb 7 Bi 4 Se 13 based lillianites, with a peak figure of merit, zT of 1.35 at 800 K and a high average zT of 0.92 (450–800 K). A unique quality factor is established to predict and evaluate thermoelectric performances. It considers both band nonparabolicity and band gaps, commonly negligible in conventional quality factors. Such appealing performance is attributed to the convergence of effectively nested conduction bands, providing a high number of valley degeneracy, and a low thermal conductivity, stemming from large lattice anharmonicity, low-frequency localized Einstein modes and the coexistence of high-density moiré fringes and nanoscale defects. This work rekindles the vision that Pb 7 Bi 4 Se 13 based lillianites are promising candidates for highly efficient thermoelectric energy conversion.