Coinage-Metal-Stuffed Eu9Cd4Sb9: Metallic Compounds with Anomalous Low Thermal Conductivities

Nasrin Kazem, Julia V. Zaikina, Saneyuki Ohno, G. Jeffrey Snyder, Susan M. Kauzlarich

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

The synthesis and transport properties of the family of coinage metal-stuffed Zintl compounds, Eu9Cd4-xCM2yySb9 (CM = coinage metal, □ = vacancies), is presented as a function of coinage metal substitution. Eu9Cd4-xCM2yySb9 compounds are shown to be rare examples of metallic Zintl phases with low thermal conductivities. While the lattice thermal conductivity is low, which is attributed to the complex structure and presence of interstitials, the electronic contribution to thermal conductivity is also low. In these p-type compounds, the carriers transmit less heat than expected, based on the Wiedemann-Franz law and metallic conduction, κe = L0T/φ. Density functional theory (DFT) calculations indicate that the Fermi level resides in a pseudo-gap, which is consistent with the metallic description of the properties. While the contribution from the interstitial CM states to the Fermi level is small, the interstitial CMs are required to tune the position of the Fermi level. Analysis of the topology of electron localization function (ELF) basins reveals the multicenter Eu-Cd(CM)-Sb interactions, as the Eu and Sb states have the largest contribution at the top of the valence band. Regardless of the success of the Zintl concept in the rationalization of the properties, the representation of the CM-stuffed Eu9Cd4Sb9 structure as Eu cations encapsulated into a polyanionic (Cd/Cu)Sb network is oversimplified and underestimates the importance of the Eu-Sb bonding interactions. These results provide motivation to search for more efficient thermoelectric materials among complex metallic structures that can offer less electronic thermal conductivity without deteriorating the electrical conductivity.

Original languageEnglish (US)
Pages (from-to)7508-7519
Number of pages12
JournalChemistry of Materials
Volume27
Issue number21
DOIs
StatePublished - Nov 10 2015

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Coinage
Metallic compounds
Thermal conductivity
Fermi level
Metals
Valence bands
Transport properties
Vacancies
Density functional theory
Cations
Substitution reactions
Positive ions
Topology
Electrons

ASJC Scopus subject areas

  • Materials Chemistry
  • Chemical Engineering(all)
  • Chemistry(all)

Cite this

Coinage-Metal-Stuffed Eu9Cd4Sb9 : Metallic Compounds with Anomalous Low Thermal Conductivities. / Kazem, Nasrin; Zaikina, Julia V.; Ohno, Saneyuki; Snyder, G. Jeffrey; Kauzlarich, Susan M.

In: Chemistry of Materials, Vol. 27, No. 21, 10.11.2015, p. 7508-7519.

Research output: Contribution to journalArticle

Kazem, Nasrin ; Zaikina, Julia V. ; Ohno, Saneyuki ; Snyder, G. Jeffrey ; Kauzlarich, Susan M. / Coinage-Metal-Stuffed Eu9Cd4Sb9 : Metallic Compounds with Anomalous Low Thermal Conductivities. In: Chemistry of Materials. 2015 ; Vol. 27, No. 21. pp. 7508-7519.
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abstract = "The synthesis and transport properties of the family of coinage metal-stuffed Zintl compounds, Eu9Cd4-xCM2y□ySb9 (CM = coinage metal, □ = vacancies), is presented as a function of coinage metal substitution. Eu9Cd4-xCM2y□ySb9 compounds are shown to be rare examples of metallic Zintl phases with low thermal conductivities. While the lattice thermal conductivity is low, which is attributed to the complex structure and presence of interstitials, the electronic contribution to thermal conductivity is also low. In these p-type compounds, the carriers transmit less heat than expected, based on the Wiedemann-Franz law and metallic conduction, κe = L0T/φ. Density functional theory (DFT) calculations indicate that the Fermi level resides in a pseudo-gap, which is consistent with the metallic description of the properties. While the contribution from the interstitial CM states to the Fermi level is small, the interstitial CMs are required to tune the position of the Fermi level. Analysis of the topology of electron localization function (ELF) basins reveals the multicenter Eu-Cd(CM)-Sb interactions, as the Eu and Sb states have the largest contribution at the top of the valence band. Regardless of the success of the Zintl concept in the rationalization of the properties, the representation of the CM-stuffed Eu9Cd4Sb9 structure as Eu cations encapsulated into a polyanionic (Cd/Cu)Sb network is oversimplified and underestimates the importance of the Eu-Sb bonding interactions. These results provide motivation to search for more efficient thermoelectric materials among complex metallic structures that can offer less electronic thermal conductivity without deteriorating the electrical conductivity.",
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