Vankayala RK, Lan T, Parajuli P, Liu F, Rao R, Yu SH, Hung T, Lee C, Yano S, Hsing C, Nguyen D, Chen C, Bhattacharya S, Chen K, Ou M, Rancu O, Rao AM, Chen Y. High
zT and Its Origin in Sb-doped GeTe Single Crystals.
Adv Sci (Weinh) 2020;
7:2002494. [PMID:
33344133 PMCID:
PMC7740100 DOI:
10.1002/advs.202002494]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 09/10/2020] [Indexed: 05/14/2023]
Abstract
A record high zT of 2.2 at 740 K is reported in Ge0.92Sb0.08Te single crystals, with an optimal hole carrier concentration ≈4 × 1020 cm-3 that simultaneously maximizes the power factor (PF) ≈56 µW cm-1 K-2 and minimizes the thermal conductivity ≈1.9 Wm-1 K-1. In addition to the presence of herringbone domains and stacking faults, the Ge0.92Sb0.08Te exhibits significant modification to phonon dispersion with an extra phonon excitation around ≈5-6 meV at Γ point of the Brillouin zone as confirmed through inelastic neutron scattering (INS) measurements. Density functional theory (DFT) confirmed this phonon excitation, and predicted another higher energy phonon excitation ≈12-13 meV at W point. These phonon excitations collectively increase the number of phonon decay channels leading to softening of phonon frequencies such that a three-phonon process is dominant in Ge0.92Sb0.08Te, in contrast to a dominant four-phonon process in pristine GeTe, highlighting the importance of phonon engineering approaches to improving thermoelectric (TE) performance.
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