Thermoelectric properties of Cu-doped dysprosium sesquisulfide

The electrical resistivity, thermoelectric power (Seebeck coefficient), Hall effect, and thermal conductivity have been measured in Cux(Dy2S3)1−x compounds with the η-orthorhombic structure in the composition range 0.006≤x≤0.15 in order to determine their potential as high temperature (300–1000 °C) thermoelectric materials. In this temperature and composition range Cu-doped Dy2S3 behaves as a degenerate semiconductor and shows itinerant conduction. The electrical resistivity and the Seebeck coefficient increased with increasing temperature and reach a maximum value of 4.35–7.13 mΩ cm and −163 to −177 μV/°C, respectively, depending upon the Cu concentration. A maximum power factor of 7.9 μW/cm °C2 for the Cu0.039(Dy2S3)0.961 alloy was observed at 690 °C. The 300–1000 °C integrated average power factor shows that the optimum Cu-doping level in the Dy2S3 matrix is 5–7 at. %. The thermal conductivity of Cu0.039(Dy2S3)0.961 decreased with increasing temperature from 300 to 1000 °C and was governed by both electronic and lattice contributions up to 600 °C, but above 600 °C the electronic contribution is predominant. The 300–1000 °C integrated average thermal conductivity of Cu0.039(Dy2S3)0.961 is 18.38 mW/cm °C, which gives this material a maximum figure of merit Z of 0.440×10−3/°C at 800 °C.