Fabrication of Non-Stoichiometric Titanium Dioxide by Spark Plasma Sintering and Its Thermoelectric Properties

Abstract

To obtain non-stoichiometric titanium dioxide, TiO 2 powder was sintered in a graphite die by spark plasma sintering (SPS). The microstructure and the crystal type of the compacts were examined. Thermoelectric properties of the compacts were measured and discussed. The results revealed that TiO 2 could be easy to be reduced in the graphite die by SPS to obtain non-stoichiometric titanium dioxide, TiO 2¹x with uniform composition distribution. Electrical resistivity of the compacts decreased with increase of SPS temperature. Seebeck coefficient also decreased with increase of SPS temperature, but kept large absolute values over 300 µV·K ¹1. Therefore, the compacts fabricated by SPS showed relatively high thermoelectric performance. The power factor reached 5 © 10 ¹5 W m ¹1 K

Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr0.1Ce0.9O2−δ Case Study

“…Many physical and chemical properties are often strong functions of δ including, for example, electrical conductivity, magnetic permeability, optical absorptivity and luminescence, oxygen and cation diffusivities, and thermal conductivity . As an illustrative example, the room temperature electrical conductivity of TiO 2‐δ can differ by many orders of magnitude as δ varies from near zero to ∼ 0.01 …”

Investigating the high-temperature thermoelectric properties of n -type rutile TiO2

“…As high-temperature generation is the main application prospect for TiO 2 as a thermolectric material, it is crucial to accurately predict the transport properties between 300 K and 2000 K. In Ref. 20, the electrical conductivity and Seebeck coefficients of reduced rutile samples, subjected to spark plasma sintering (SPS) at different temperatures, have been measured up to 523 K. The conductivity displays a very weak temperature dependance, even though the scattering rate, equation ( 5), increases substantially with elevated temperature. This suggests an activation mechanism for the electron density in the conduction band, as confirmed by the Hall measurements in Ref.…”

“…Of these, rutile is particularly stable at high temperatures with a melting point around 2100 K, while anatase and brookite undergo a phase transition to rutile near 1000 K. Additionally, the carrier concentration of rutile can be tuned by doping with several elements such as boron, niobium or cobalt, or by using reduction processes to introduce oxygen vacancies acting as electron donors. [17][18][19][20] Therefore, this compound would represent a very promising prospect for waste heat recovery applications if its thermoelectric properties could be optimized. 21 In this paper, we investigate the electron transport properties of n-type rutile TiO 2 by combining first-principle calculations with a modelling of electronphonon interactions and donor defects.…”

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

“…10,11) It suggests the combination of SPS and the following reduction treatment is effective and feasible to improve the thermoelectric performance of TiO 2 . For the unpolished sample ( Fig.…”

“…The measurement method of thermoelectric properties has been described and can be found in our early work 11) and it will not be involved here. The Seebeck coefficient and electrical resistivity were measured by the static method and 4-probe method respectively in air from room temperature up to 573 K. In that temperature range, the re-oxidation effect on the thermoelectric properties was rather weak and can be neglected.…”