title: Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics.
abstract: In this paper, we systematically investigate three different routes of synthesizing 2% Na-doped PbTe after melting the elements: (i) quenching followed by hot-pressing (QH), (ii) annealing followed by hot-pressing, and (iii) quenching and annealing followed by hot-pressing. We found that the thermoelectric figure of merit, zT, strongly depends on the synthesis condition and that its value can be enhanced to ∼ 2.0 at 773 K by optimizing the size distribution of the nanostructures in the material. Based on our theoretical analysis on both electron and thermal transport, this zT enhancement is attributed to the reduction of both the lattice and electronic thermal conductivities; the smallest sizes (2 ∼ 6 nm) of nanostructures in the QH sample are responsible for effectively scattering the wide range of phonon wavelengths to minimize the lattice thermal conductivity to ∼ 0.5 W/m K. The reduced electronic thermal conductivity associated with the suppressed electrical conductivity by nanostructures also helped reduce the total thermal conductivity. In addition to the high zT of the QH sample, the mechanical hardness is higher than the other samples by a factor of around 2 due to the smaller grain sizes. Overall, this paper suggests a guideline on how to achieve high zT and mechanical strength of a thermoelectric material by controlling nano- and microstructures of the material.
authors.affiliation: School of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea;
authors.forename: Hongchao
authors.initials: H
authors.lastname: Wang
authors.affiliation: Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907; and.
authors.forename: Je-Hyeong
authors.initials: JH
authors.lastname: Bahk
authors.affiliation: School of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea;
authors.forename: Chanyoung
authors.initials: C
authors.lastname: Kang
authors.affiliation: School of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea;
authors.forename: Junphil
authors.initials: J
authors.lastname: Hwang
authors.affiliation: School of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea;
authors.forename: Kangmin
authors.initials: K
authors.lastname: Kim
authors.affiliation: School of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea;
authors.forename: Jungwon
authors.initials: J
authors.lastname: Kim
authors.affiliation: Materials Department, University of California, Santa Barbara, CA 93106.
authors.forename: Peter
authors.initials: P
authors.lastname: Burke
authors.affiliation: Materials Department, University of California, Santa Barbara, CA 93106.
authors.forename: John E
authors.initials: JE
authors.lastname: Bowers
authors.affiliation: Materials Department, University of California, Santa Barbara, CA 93106.
authors.forename: Arthur C
authors.initials: AC
authors.lastname: Gossard
authors.affiliation: Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907; and.
authors.forename: Ali
authors.initials: A
authors.lastname: Shakouri
authors.affiliation: School of Mechanical Engineering, Yonsei University, Seoul 120-749, Korea; woochul@yonsei.ac.kr.
authors.forename: Woochul
authors.initials: W
authors.lastname: Kim
keywords: energy harvesting; waste heat recovery