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Crystals 2017, 7(9), 271; doi:10.3390/cryst7090271

Spark Plasma Sintering of Tungsten Oxides WOx (2.50 ≤ x ≤ 3): Phase Analysis and Thermoelectric Properties

1
Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany
2
Fraunhofer Institut für Fertigungstechnik und Angewandte Materialforschung, 01277 Dresden, Germany
*
Authors to whom correspondence should be addressed.
Academic Editor: George S. Nolas
Received: 26 July 2017 / Revised: 21 August 2017 / Accepted: 23 August 2017 / Published: 5 September 2017
(This article belongs to the Special Issue Materials Processing and Crystal Growth for Thermoelectrics)
View Full-Text   |   Download PDF [7889 KB, uploaded 5 September 2017]   |  

Abstract

The solid-state reaction of WO3 with W was studied in order to clarify the phase formation in the binary system W-O around the composition WOx (2.50 ≤ x ≤ 3) during spark plasma sintering (SPS). A new phase “WO2.82” is observed in the range 2.72 ≤ x ≤ 2.90 which might have the composition W12O34. The influence of the composition on the thermoelectric properties was investigated for 2.72 ≤ x ≤ 3. The Seebeck coefficient, electrical conductivity and electronic thermal conductivity are continuously tunable with the oxygen-to-tungsten ratio. The phase formation mainly affects the lattice thermal conductivity κlat which is significantly reduced until 700 K for the sample with the composition x = 2.84, which contains the phases W18O49 and “WO2.82”. In single-phase WO2.90 and multi-phase WOx materials (2.90 ≤ x ≤ 3), which contain crystallographic shear plane phases, a similar reduced κlat is observed only below 560 K and 550 K, respectively. Therefore, the composition range x < 2.90 in which the pentagonal column structural motif is formed might be more suitable for decreasing the lattice thermal conductivity at high temperatures. View Full-Text
Keywords: thermoelectric materials; spark plasma sintering; tungsten oxides; crystallographic shear plane phases thermoelectric materials; spark plasma sintering; tungsten oxides; crystallographic shear plane phases
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Kaiser, F.; Simon, P.; Burkhardt, U.; Kieback, B.; Grin, Y.; Veremchuk, I. Spark Plasma Sintering of Tungsten Oxides WOx (2.50 ≤ x ≤ 3): Phase Analysis and Thermoelectric Properties. Crystals 2017, 7, 271.

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