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

Abstract

Compacts of non-stoichiometric TiO 2¹x 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 TiO 2¹x 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 µm when it came to 20 h. Carbon did not penetrate into the compacts during the reduction treatment. To examine the carrier density and the non-stoichiometric number, 2 ¹ x, thermogravimetry was carried out. The study showed that the value of 2 ¹ 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 µV·K ¹1 at 573 K. Power factor reached 2 © 10 ¹4 W·m ¹1 ·K ¹2 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.

Reduction of Contact Resistance on Titanium Sheet Surfaces by Formation of Titanium Carbide and Nitride, and its Stability in Sulfuric Acid Aqueous Solution

“…It is known that TiO 2 − x made by introducing oxygen deficiency into TiO 2 (nonconductor) becomes an n-type semiconductor, showing conductivity. [33][34][35] If nitric acid immersion works to reduce the oxygen deficiency in oxide films, it can be assumed that it does not enhance the conductivity.…”

High-Pressure and High-Temperature Synthesis and Pressure-Induced Simultaneous Optimization of the Electrical and Thermal Transport Properties of Nonstoichiometric TiO1.80

“…It is needed to point out that all resultant samples are black-blue, indicating the formation of oxygen vacancies. 7,20 Collectively, all of these manifest the reduction to TiO 2 . The high-pressure extrusion and the ability of titanium to pillage oxygen under high temperature created the strong reducing environment.…”

FEM Analysis on Thermoelectric Properties of Metal/TiO_2–x Composites with Random Distribution of Metal Powder

“…Therefore, metal powder addition into thermoelectric oxides (e.g. Ni/TiO 2−x , Ag/Ca 3 Co 4 O 9 and others [1][2][3][4][5][6][7][8]) is generally used to decrease electrical resistivity as one method for performance improvement. Although electrical resistivity of thermoelectric materials can be decreased largely by the metal addition, it is always accompanied with some negative effects such as thermal conductivity increase.…”