title: Higher thermoelectric performance of Zintl phases (Eu0.5Yb0.5)1-xCaxMg2Bi2 by band engineering and strain fluctuation.
abstract: Complex Zintl phases, especially antimony (Sb)-based YbZn0.4Cd1.6Sb2 with figure-of-merit (ZT) of ∼1.2 at 700 K, are good candidates as thermoelectric materials because of their intrinsic "electron-crystal, phonon-glass" nature. Here, we report the rarely studied p-type bismuth (Bi)-based Zintl phases (Ca,Yb,Eu)Mg2Bi2 with a record thermoelectric performance. Phase-pure EuMg2Bi2 is successfully prepared with suppressed bipolar effect to reach ZT ∼ 1. Further partial substitution of Eu by Ca and Yb enhanced ZT to ∼1.3 for Eu0.2Yb0.2Ca0.6Mg2Bi2 at 873 K. Density-functional theory (DFT) simulation indicates the alloying has no effect on the valence band, but does affect the conduction band. Such band engineering results in good p-type thermoelectric properties with high carrier mobility. Using transmission electron microscopy, various types of strains are observed and are believed to be due to atomic mass and size fluctuations. Point defects, strain, dislocations, and nanostructures jointly contribute to phonon scattering, confirmed by the semiclassical theoretical calculations based on a modified Debye-Callaway model of lattice thermal conductivity. This work indicates Bi-based (Ca,Yb,Eu)Mg2Bi2 is better than the Sb-based Zintl phases.
authors.affiliation: Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX 77204;
authors.forename: Jing
authors.initials: J
authors.lastname: Shuai
authors.affiliation: School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China;
authors.forename: Huiyuan
authors.initials: H
authors.lastname: Geng
authors.affiliation: Department of Physics and Engineering Physics, Morgan State University, Baltimore, MD 21251;
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Lan
authors.affiliation: Department of Mechanical Engineering, University of Houston, Houston, TX 77204;
authors.forename: Zhuan
authors.initials: Z
authors.lastname: Zhu
authors.affiliation: State Key Lab of Electronic Thin Film and Integrated Device, University of Electric Science and Technology of China, Chengdu 611731, China;
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX 77204; School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China;
authors.forename: Zihang
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Mechanical Engineering, University of Houston, Houston, TX 77204;
authors.forename: Jiming
authors.initials: J
authors.lastname: Bao
authors.affiliation: Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX 77204; Lawrence Berkeley National Laboratory, Berkeley, CA 94720 cwchu@uh.edu suijiehe@hit.edu.cn zren@uh.edu.
authors.forename: Ching-Wu
authors.initials: CW
authors.lastname: Chu
authors.affiliation: School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China; cwchu@uh.edu suijiehe@hit.edu.cn zren@uh.edu.
authors.forename: Jiehe
authors.initials: J
authors.lastname: Sui
authors.affiliation: Department of Physics and Texas Center for Superconductivity, University of Houston, Houston, TX 77204; cwchu@uh.edu suijiehe@hit.edu.cn zren@uh.edu.
authors.forename: Zhifeng
authors.initials: Z
authors.lastname: Ren
keywords: Bi-based Zintl phases; band engineering; strain-field fluctuation; thermoelectric properties