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Grain boundary dominated charge transport in Mg_3Sb_2-based compounds

Kuo, Jimmy Jiahong and Kang, Stephen Dongmin and Imasato, Kazuki and Tamaki, Hiromasa and Ohno, Saneyuki and Kanno, Tsutomu and Snyder, G. Jeffrey (2018) Grain boundary dominated charge transport in Mg_3Sb_2-based compounds. Energy and Environmental Science, 11 (2). pp. 429-434. ISSN 1754-5692. https://resolver.caltech.edu/CaltechAUTHORS:20180119-160624082

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Abstract

Thermally activated mobility near room temperature is a signature of detrimental scattering that limits the efficiency and figure-of-merit zT in thermoelectric semiconductors. This effect has been observed dramatically in Mg_3Sb_2-based compounds, but also to a lesser extent in other thermoelectric compounds. Processing samples differently or adding impurities such that this effect is less noticeable produces materials with a higher zT. Experiments suggest that the behavior is related to grain boundaries, but impurity scattering has also been proposed. However, conventional models using Matthissen's rule are not able to explain the dramatic change in the temperature dependency of conductivity or drift mobility which is observed in Mg3Sb2-based compounds. We find that it is essential to consider the grain boundary region as an effectively separate phase rather than a scattering center, taking into account the weaker screening in semiconductors compared with classical metals. By modeling a grain boundary phase with a band offset, we successfully reproduce the experimentally observed conductivity versus temperature and thermopower versus conductivity relations, which indicate an improved description of transport. The model shows good agreement with measured grain size dependencies of conductivity, opening up avenues for quantitatively engineering materials with similar behavior. Model estimates predict room for >60% improvement in the room temperature zT of Mg_(3.2)Sb_(1.5)Bi_(0.49)Te_(0.01) if the grain boundary resistance could be eliminated.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1039/c7ee03326eDOIArticle
http://pubs.rsc.org/en/Content/ArticleLanding/2018/EE/C7EE03326EPublisherArticle
http://www.rsc.org/suppdata/c7/ee/c7ee03326e/c7ee03326e1.pdfPublisherSupplementary Information
ORCID:
AuthorORCID
Kuo, Jimmy Jiahong0000-0002-3434-1984
Kang, Stephen Dongmin0000-0002-7491-7933
Imasato, Kazuki0000-0001-7294-1780
Tamaki, Hiromasa0000-0002-4717-0272
Ohno, Saneyuki0000-0001-8192-996X
Kanno, Tsutomu0000-0001-5412-4410
Snyder, G. Jeffrey0000-0003-1414-8682
Alternate Title:Grain boundary dominated charge transport in Mg3Sb2-based compounds
Additional Information:© 2017 The Royal Society of Chemistry. The article was received on 22 Nov 2017, accepted on 13 Dec 2017 and first published on 19 Jan 2018. The authors would like to acknowledge support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences through the Solid-State Solar-Thermal Energy Conversion Center (S3TEC), an Energy Frontier Research Center (DE-SC0001299), and also from the NASA Science Mission Directorate's Radioisotope Power Systems Thermoelectric Technology Development program. KI acknowledges support from Funai Foundation for Information Technology. There are no conflicts to declare.
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0001299
NASAUNSPECIFIED
Funai Foundation for Information TechnologyUNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20180119-160624082
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180119-160624082
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84435
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Jan 2018 00:19
Last Modified:03 Oct 2019 19:18

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