Improvement in Thermoelectric Properties of Non-Stoichiometric Titanium Dioxide by Reduction Treatment

Compacts of non-stoichiometric TiO2-x were fabricated by SPS and the following reduction treatment in carbon powder. XRD, SEM and EPMA were used to characterize the compacts. The results showed that they were composed of non-stoichiometric TiO2-x inside and TiO as the surface layer. The thickness of the surface layer was increased with the increase of the holding time and exceeded 100 urn when it came to 20h. Carbon did not penetrate into the compacts during the reduction treatment. To examine the carrier density and the non-stoichiometric number, 2 - x, thermogravimetry was carried out. The study showed that the value of 2 - x was decreased and the carrier density was increased as the holding time increased. The thermoelectric properties including electrical resistivity, Seebeck coefficient and power factor was measured. The electric resistivity was considerably reduced by the reduction treatment. The values of the Seebeck coefficient was also decreased by the reduction treatment but maintained at a large absolute value of 250 mu V.k(-1) at 573 K. Power factor reached 2 x 10(-4)W.m(-1)-K-2 at 573 K. The value was much higher than that of the samples by SPS only. Therefore, the thermoelectric performance was improved by the reduction treatment. The influence of the TiO layer on the thermoelectric performance was also examined. It was believed that the influence should result from its comprehensive effect on Seebeck coefficient and electrical resistivity.