TY - JOUR
T1 - Thermal conductivity in Bi0.5Sb1.5Te3+x and the role of dense dislocation arrays at grain boundaries
AU - Deng, Rigui
AU - Su, Xianli
AU - Zheng, Zheng
AU - Liu, Wei
AU - Yan, Yonggao
AU - Zhang, Qingjie
AU - Dravid, Vinayak P.
AU - Uher, Ctirad
AU - Kanatzidis, Mercouri G.
AU - Tang, Xinfeng
N1 - Funding Information:
We thank R. Jiang and T. Luo for help with the HRTEM analysis. We acknowledge support from the Natural Science Foundation of China (grant nos. 51521001 and 51632006), the Fundamental Research Funds for the Central Universities (Wuhan University of Technology, 162459002, 2015-061) and the 111 Project of China (grant no. B07040). This work was supported in part by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, under grant DE-SC0014520, DOE Office of Science (sample preparation, XRD, and TEM measurements).
Publisher Copyright:
Copyright © 2018 The Authors.
PY - 2018/6/1
Y1 - 2018/6/1
N2 - Several prominent mechanisms for reduction in thermal conductivity have been shown in recent years to improve the figure of merit for thermoelectric materials. Such a mechanism is a hierarchical all-length-scale architecturing that recognizes the role of all microstructure elements, from atomic to nano to microscales, in reducing (lattice) thermal conductivity. In this context, there have been recent claims of remarkably low (lattice) thermal conductivity in Bi0.5Sb1.5Te3 that are attributed to seemingly ordinary grain boundary dislocation networks. These high densities of dislocation networks in Bi0.5Sb1.5Te3 were generated via unconventional materials processing with excess Te (which formed liquid phase, thereby facilitating sintering), followed by spark plasma sintering under pressure to squeeze out the liquid. We reproduced a practically identical microstructure, following practically identical processing strategies, but with noticeably different (higher) thermal conductivity than that claimed before. We show that the resultant microstructure is anisotropic, with notable difference of thermal and charge transport properties across and along two orthonormal directions, analogous to anisotropic crystals. Thus, we believe that grain boundary dislocation networks are not the primary cause of enhanced ZT through reduction in thermal conductivity. Instead, we can reproduce the purported high ZT through a favorable but impractical and incorrect combination of thermal conductivity measured along the pressing direction of anisotropy while charge transport measured in the direction perpendicular to the anisotropic direction. We believe that our work underscores the need for consistency in charge and thermal transport measurements for unified and verifiable measurements of thermoelectric (and related) properties and phenomena.
AB - Several prominent mechanisms for reduction in thermal conductivity have been shown in recent years to improve the figure of merit for thermoelectric materials. Such a mechanism is a hierarchical all-length-scale architecturing that recognizes the role of all microstructure elements, from atomic to nano to microscales, in reducing (lattice) thermal conductivity. In this context, there have been recent claims of remarkably low (lattice) thermal conductivity in Bi0.5Sb1.5Te3 that are attributed to seemingly ordinary grain boundary dislocation networks. These high densities of dislocation networks in Bi0.5Sb1.5Te3 were generated via unconventional materials processing with excess Te (which formed liquid phase, thereby facilitating sintering), followed by spark plasma sintering under pressure to squeeze out the liquid. We reproduced a practically identical microstructure, following practically identical processing strategies, but with noticeably different (higher) thermal conductivity than that claimed before. We show that the resultant microstructure is anisotropic, with notable difference of thermal and charge transport properties across and along two orthonormal directions, analogous to anisotropic crystals. Thus, we believe that grain boundary dislocation networks are not the primary cause of enhanced ZT through reduction in thermal conductivity. Instead, we can reproduce the purported high ZT through a favorable but impractical and incorrect combination of thermal conductivity measured along the pressing direction of anisotropy while charge transport measured in the direction perpendicular to the anisotropic direction. We believe that our work underscores the need for consistency in charge and thermal transport measurements for unified and verifiable measurements of thermoelectric (and related) properties and phenomena.
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U2 - 10.1126/sciadv.aar5606
DO - 10.1126/sciadv.aar5606
M3 - Article
C2 - 29868641
AN - SCOPUS:85048282132
VL - 4
JO - Science advances
JF - Science advances
SN - 2375-2548
IS - 6
M1 - eaar5606
ER -