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Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide

Heinrich, Christophe P. and Schrade, Matthias and Cerretti, Giacomo and Lieberwirth, Ingo and Leidich, Patrick and Schmitz, Andreas and Fjeld, Harald and Müller, Eckhard and Finstad, Terje G. and Norby, Truls and Tremel, Wolfgang (2015) Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide. Materials Horizons, 2 (5), pp. 519-527. Royal Society of Chemistry. DOI: 10.1039/C5MH00033E ISSN 2051-6347

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Abstract

Engineering of nanoscaled structures may help controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require the combination of low thermal conductivity and low electrical resistivity. The tetragonal tungsten bronzes Nb8−xW9+xO47 (TTB) allow a continuous variation of the charge carrier concentration while fulfilling at the same time the concept of a “phonon-glass electron-crystal” through a layered nanostructure defined by intrinsic crystallographic shear planes. The thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47−δ (0 < x < 2) were studied in the temperature range from 373 to 973 K. Structural defects and the thermal stability under various oxygen partial pressure pO2 were investigated by means of thermogravimetry, HR-TEM, and XRD. Nb8W9O47−δ was found stable at 973 K and a pO2 of ≈10−15 atm. The oxygen nonstoichiometry δ can reach up to 0.3, depending on the applied atmosphere. By increasing the substitution level x, the electrical resistivity ρ and the Seebeck coefficient S decreased. For x = 2, ρ reached 20 mΩ cm at 973 K, combined with a Seebeck coefficient of approximately −120 μV K−1. The thermal conductivity was low for all samples, ranging from 1.6 to 2.0 W K−1 m−1, attributed to the complex crystal structure. The best thermoelectric figure of merit zT of the investigated samples was 0.043, obtained for x = 2 at 973 K, but it is expected to increase significantly upon a further increase of x. The control of the oxygen non-stoichiometry δ opens a second independent optimization strategy for tetragonal tungsten bronzes.

Item URL in elib:https://elib.dlr.de/100084/
Document Type:Article
Title:Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Heinrich, Christophe P.Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, Germany and Graduate School Materials Science in Mainz, Johannes Gutenberg-Universität, Staudinger Weg 9, 55128 Mainz, GermanyUNSPECIFIED
Schrade, MatthiasCentre for Materials Science and Nanotechnology, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, NorwayUNSPECIFIED
Cerretti, GiacomoInstitut für Anorganische Chemie und Analytische Chemie der Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, GermanyUNSPECIFIED
Lieberwirth, IngoMax Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz, GermanyUNSPECIFIED
Leidich, PatrickInstitut für Anorganische Chemie und Analytische Chemie der Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, GermanyUNSPECIFIED
Schmitz, AndreasGerman Aerospace Center, Institute of Materials Research, Köln, GermanyUNSPECIFIED
Fjeld, HaraldCentre for Materials Science and Nanotechnology, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, NorwayUNSPECIFIED
Müller, EckhardGerman Aerospace Center, Institute of Materials Research, Köln, Germany and Justus Liebig University Giessen, Institute of Inorganic and Analytical Chemistry, 35392 Giessen, GermanyUNSPECIFIED
Finstad, Terje G.Centre for Materials Science and Nanotechnology, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, NorwayUNSPECIFIED
Norby, TrulsCentre for Materials Science and Nanotechnology, University of Oslo, FERMiO, Gaustadalléen 21, NO-0349 Oslo, NorwayUNSPECIFIED
Tremel, WolfgangInstitut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, GermanyUNSPECIFIED
Date:3 July 2015
Journal or Publication Title:Materials Horizons
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:2
DOI :10.1039/C5MH00033E
Page Range:pp. 519-527
Publisher:Royal Society of Chemistry
ISSN:2051-6347
Status:Published
Keywords:n-type thermoelectric oxide, transport properties
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:propulsion systems
DLR - Research area:Aeronautics
DLR - Program:L ER - Engine Research
DLR - Research theme (Project):L - Turbine Technologies
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > Thermoelectric Materials and Systems
Deposited By: Zabrocki, Dr. Knud
Deposited On:30 Nov 2015 08:31
Last Modified:08 Mar 2018 18:38

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