title: Compromise and Synergy in High-Efficiency Thermoelectric Materials.
abstract: The past two decades have witnessed the rapid growth of thermoelectric (TE) research. Novel concepts and paradigms are described here that have emerged, targeting superior TE materials and higher TE performance. These superior aspects include band convergence, "phonon-glass electron-crystal", multiscale phonon scattering, resonant states, anharmonicity, etc. Based on these concepts, some new TE materials with distinct features have been identified, including solids with high band degeneracy, with cages in which atoms rattle, with nanostructures at various length scales, etc. In addition, the performance of classical materials has been improved remarkably. However, the figure of merit zT of most TE materials is still lower than 2.0, generally around 1.0, due to interrelated TE properties. In order to realize an "overall zT > 2.0," it is imperative that the interrelated properties are decoupled more thoroughly, or new degrees of freedom are added to the overall optimization problem. The electrical and thermal transport must be synergistically optimized. Here, a detailed discussion about the commonly adopted strategies to optimize individual TE properties is presented. Then, four main compromises between the TE properties are elaborated from the point of view of the underlying mechanisms and decoupling strategies. Finally, some representative systems of synergistic optimization are also presented, which can serve as references for other TE materials. In conclusion, some of the newest ideas for the future are discussed.
authors.affiliation: State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Tiejun
authors.initials: T
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Yintu
authors.initials: Y
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Chenguang
authors.initials: C
authors.lastname: Fu
authors.affiliation: Department of Mechanical and Aerospace Engineering, Department of Materials Science and Engineering and Department of Physics, The Ohio State University, Columbus, OH, 43210, USA.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Heremans
authors.affiliation: Department of Materials Science and Engineering, Northwestern University, Evanston, IL, 60208, USA.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Snyder
authors.affiliation: State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Xinbing
authors.initials: X
authors.lastname: Zhao
keywords: band engineering; electrical properties; nanostructuring; thermal conductivity; thermoelectrics