Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 139, Issue 31, Pages 10887-10896Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.7b05881
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Funding
- National Research Foundation of Korea (NRF) - Korean Government (MSIP) [NRF-2015R1A5A1036133]
- Institute for Basic Science [IBS-R006-D1, IBS-R006-G1]
- National Research Foundation of Korea [2015R1A5A1036133] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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SnSe emerges as a new class of thermoelectric materials since the recent discovery of an ultrahigh thermoelectric figure of merit in its single crystals. Achieving such performance in the polycrystalline counterpart is still challenging and requires fundamental understandings of its electrical and thermal transport properties as well as structural chemistry. Here we demonstrate a new strategy of improving conversion efficiency of bulk polycrystalline SnSe thermoelethics. We show that PbSe alloying decreases the transition temperature between Pnma and Cmcm phases and thereby can serve as a means of controlling its onset temperature. Along with 1% Na doping, delicate control of the alloying fraction markedly enhances electrical conductivity by earlier initiation of bipolar conduction while reducing lattice thermal conductivity by alloy and point defect scattering simultaneously. As a result, a remarkably high peak ZT of similar to 1.2 at 773 K as well as average ZT of similar to 0.5 from RT to 773 K is achieved for Na-0.01(Sn1-xPbx)(0.99)Se. Surprisingly, spherical-aberration corrected scanning transmission electron microscopic studies reveal that NaySn1-xPbxSe (0 < x <= 0.2; y = 0, 0.01) alloys spontaneously form nanoscale particles with a typical size of similar to 5-10 nm embedded inside the bulk matrix, rather than solid solutions as previously believed. This unexpected feature results in further reduction in their lattice thermal conductivity.
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