ICT2014 Abstracts

Oxides materials are expected to play an important role in extensive thermoelectric applications, thank to their various advantages, including low toxicity, thermal stability, low-cost... With a wide band gap of ~3.6 eV and very a large carrier mobility, SnO₂ could be a good semi-conductor candidate for this purpose. Non-intentionally doped SnO₂ displays n-type conductivity due to the co-existence of oxygen vacancies and interstitial tin. In order to enhance the thermoelectric properties, several doping elements could be used, such as Nb, Ta, Sb... Contrary to to numerous articles related to SnO₂-based thin-films, there are only few dealing with bulk samples. One of main raisons would be the difficulty to obtain nanostructured bulk samples.

The aim of this study was to evaluate the thermoelectric properties of Ta_xSn_1-xO₂ nanomaterials (0 < x ≤ 0.04). Powders composed of 3 nm grains (with a specific surface of ~ 140 m²/g) were prepared by a coprecipitation method. ICP elemental analysis confirmed the Ta contents of our samples, which are closed to the nominal contents. By using Spark Plasma Sintering technique (SPS), we obtained dense samples with grain-size varied from 6 to 60 nm. X-ray photoelectron Spectroscopy (XPS) was used to study the chemical environments of the elements and the structure of the valence band. Dense samples were then characterized by temperature-dependent thermoelectric measurements, including electrical resistivity, Seebeck coefficient, thermal diffusivity, heat capacity. The obtained results confirmed the incorporation of Ta inside SnO₂ lattice. Hall effect measurements evidenced an increase in the charge carriers concentration when the Ta doped content increased. The nanostructuration effect was studied for samples with grains size varied from 6 to 60 nm and will be discussed in detail during the presentation. The stability of these oxide materials as a function of the surrounding atmosphere will also be discussed.