Paper EM-WeA5
Thermoelectric Properties of Concentration Graded Bulk Co-Doped TiO₂

Wednesday, October 17, 2007, 3:00 pm, Room 612

There has been a recent increased interest in using segmented thermoelectric elements to improve the performance of the thermoelectric devices. Concentration graded of dopants in the oxides can be regarded as a segmented component composed of a single parent based material. In terms of material processing and operating temperature, concentration graded oxides is more advantageous, and may result in higher efficiency at elevated operating temperature, especially for bulk thermoelectric devices. In this work, concentration graded n-typed Co-doped TiO₂ synthesized by solid state reaction method by mixing the powder of Ti and Co oxides, followed by hot-pressed under vacuum of 3x10^-5 torr and temperature of 1473 K. The distribution of the Co doping concentration in the graded samples was mapped out by using Energy Dispersive X-ray Fluorescence Spectrometer scanning technique. The 2D X-ray diffraction measurements indicate polycrystalline Co-doped TiO₂ rutile were fabricated. The Current-Voltage characteristics under the presence of the temperature gradient were generated for selected samples by applying a current source in such a way that the thermopower current was suppressed by applied current in the opposite direction. Power factors (S²Σ) were then evaluated over a temperature range from 300 K – 800 K. Surprisingly, uniformed Co doping shows parallel declined in both conductivity and thermopower magnitude, whereas graded Co doping enhanced the power factor. This implies the enhancement of the power factor could be related to electron spin entropy effect induced by Co doping to TiO₂