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Article: Enhanced thermoelectric performance of GeTe through in situ microdomain and Ge-vacancy control

TitleEnhanced thermoelectric performance of GeTe through in situ microdomain and Ge-vacancy control
Authors
KeywordsCrystal structure
Fermi level
High resolution transmission electron microscopy
Hole concentration
Seebeck coefficient
Issue Date2019
PublisherRSC Publications. The Journal's web site is located at http://pubs.rsc.org/en/journals/journalissues/ta#!recentarticles&all
Citation
Journal of Materials Chemistry A, 2019, v. 7 n. 25, p. 15181-15189 How to Cite?
AbstractA highly reproducible sample preparation method for pure GeTe in a rhombohedral structure without converting to the cubic structure up to ∼500 °C is reported to show control of the Ge-vacancy level and the corresponding herringbone-structured microdomains. The thermoelectric figure-of-merit (ZT) for GeTe powder could be raised from ∼0.8 to 1.37 at high temperature (HT) near ∼500 °C by tuning the Ge-vacancy level through the applied reversible in situ route, which made it highly controllable and reproducible. The enhanced ZT of GeTe was found to be strongly correlated with both its significantly increased Seebeck coefficient (∼161 μV K-1 at 500 °C) and reduced thermal conductivity (∼2.62 W m-1 K-1 at 500 °C) for a sample with nearly vacancy-free thicker herringbone-structured microdomains in the suppressed rhombohedral-to-cubic structure phase transformation. The microdomain and crystal structures were identified with HR-TEM (high-resolution transmission electron microscopy) and powder X-ray diffraction (XRD), while electron probe micro-analysis (EPMA) was used to confirm the stoichiometry changes of Ge:Te. Theoretical calculations for GeTe with various Ge-vacancy levels suggested that the Fermi level shifts toward the valence band as a function of increasing the Ge-vacancy level, which is consistent with the increased hole-type carrier concentration (n) and effective mass (m∗) deduced from the Hall measurements. The uniquely prepared sample of a near-vacancy-free GeTe in a rhombohedral structure at high temperature favoured an enhanced Seebeck coefficient in view of the converging L- and Σ-bands of the heavy effective mass at the Fermi level, while the high density domain boundaries for the domain of low carrier density were shown to reduce the total thermal conductivity effectively. © 2019 The Royal Society of Chemistry.
Persistent Identifierhttp://hdl.handle.net/10722/272244
ISSN
2020 Impact Factor: 12.732
2020 SCImago Journal Rankings: 3.637
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorBayikadi, KS-
dc.contributor.authorSankar, R-
dc.contributor.authorWu, CT-
dc.contributor.authorXIA, C-
dc.contributor.authorChen, Y-
dc.contributor.authorChen, L-C-
dc.contributor.authorChen, K-H-
dc.contributor.authorChou, F-C-
dc.date.accessioned2019-07-20T10:38:30Z-
dc.date.available2019-07-20T10:38:30Z-
dc.date.issued2019-
dc.identifier.citationJournal of Materials Chemistry A, 2019, v. 7 n. 25, p. 15181-15189-
dc.identifier.issn2050-7488-
dc.identifier.urihttp://hdl.handle.net/10722/272244-
dc.description.abstractA highly reproducible sample preparation method for pure GeTe in a rhombohedral structure without converting to the cubic structure up to ∼500 °C is reported to show control of the Ge-vacancy level and the corresponding herringbone-structured microdomains. The thermoelectric figure-of-merit (ZT) for GeTe powder could be raised from ∼0.8 to 1.37 at high temperature (HT) near ∼500 °C by tuning the Ge-vacancy level through the applied reversible in situ route, which made it highly controllable and reproducible. The enhanced ZT of GeTe was found to be strongly correlated with both its significantly increased Seebeck coefficient (∼161 μV K-1 at 500 °C) and reduced thermal conductivity (∼2.62 W m-1 K-1 at 500 °C) for a sample with nearly vacancy-free thicker herringbone-structured microdomains in the suppressed rhombohedral-to-cubic structure phase transformation. The microdomain and crystal structures were identified with HR-TEM (high-resolution transmission electron microscopy) and powder X-ray diffraction (XRD), while electron probe micro-analysis (EPMA) was used to confirm the stoichiometry changes of Ge:Te. Theoretical calculations for GeTe with various Ge-vacancy levels suggested that the Fermi level shifts toward the valence band as a function of increasing the Ge-vacancy level, which is consistent with the increased hole-type carrier concentration (n) and effective mass (m∗) deduced from the Hall measurements. The uniquely prepared sample of a near-vacancy-free GeTe in a rhombohedral structure at high temperature favoured an enhanced Seebeck coefficient in view of the converging L- and Σ-bands of the heavy effective mass at the Fermi level, while the high density domain boundaries for the domain of low carrier density were shown to reduce the total thermal conductivity effectively. © 2019 The Royal Society of Chemistry.-
dc.languageeng-
dc.publisherRSC Publications. The Journal's web site is located at http://pubs.rsc.org/en/journals/journalissues/ta#!recentarticles&all-
dc.relation.ispartofJournal of Materials Chemistry A-
dc.subjectCrystal structure-
dc.subjectFermi level-
dc.subjectHigh resolution transmission electron microscopy-
dc.subjectHole concentration-
dc.subjectSeebeck coefficient-
dc.titleEnhanced thermoelectric performance of GeTe through in situ microdomain and Ge-vacancy control-
dc.typeArticle-
dc.identifier.emailChen, Y: yuechen@hku.hk-
dc.identifier.authorityChen, Y=rp01925-
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1039/C9TA03503F-
dc.identifier.scopuseid_2-s2.0-85068189187-
dc.identifier.hkuros298974-
dc.identifier.volume7-
dc.identifier.issue25-
dc.identifier.spage15181-
dc.identifier.epage15189-
dc.identifier.isiWOS:000473054500020-
dc.publisher.placeUnited Kingdom-
dc.identifier.issnl2050-7496-

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