Spark plasma sintering of tungsten oxides WOx (2.50 ⤠x ⤠3): Phase analysis and thermoelectric properties

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 âWO2.82â 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 âWO2.82â. 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. Therefor e, 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. © 2017 by the authors. Licensee MDPI, Basel, Switzerland.