Enhanced thermoelectric properties of the n-type Magnéli phase WO2.90: reduced thermal conductivity through microstructure engineering

Abstract

The thermoelectric properties of the Magnéli phase WO_2.90 were investigated, with special attention to how the thermoelectric performance can be altered by changing its microstructure. Spark plasma sintering (SPS) allowed the direct preparation of large amounts of consolidated material. Adding Ta₂O₅ to the reaction mixture lead to the formation of solid solutions W_1−xTa_xO_2.90via a concurrent reaction between WO₃ and Ta₂O₅ during the SPS treatment. In addition, micron-sized inclusions containing tungsten surrounded by WO_x embedded in a WO_2.90 matrix were formed, which act as additional scattering centers. As a result, the thermal conductivity of the Ta-containing samples was reduced by ≈30% over the temperature range from 300 to 1100 K while the electronic properties remained unaffected, which in turn enhanced the thermoelectric performance and led to a relatively high zT value of 0.15 at 1100 K for n-type metal oxides.