Exploring the potential of laser processing for designing TiO2-based thermoelectric materials

abstract

The prospects for processing Ta-substituted titanium dioxide (TiO2) for thermoelectric applications were explored in this work using the Laser Floating Zone (LFZ) method under different growth atmospheres, specifically air and H2/N2. An intermediate approach, where the samples were initially LFZ-grown in air and subsequently post-annealed in H2/N2, was also evaluated to gain deeper insights into the effects of the processing conditions. XRD results revealed rutile as the majority phase regardless of the applied conditions. The phase composition was found to be strongly affected by the growth atmosphere, from the formation of TiTa2O7 to Magneli phase-based impurities when shifting from oxidising to reducing conditions. The formation of Magneli phases was favoured by lower tantalum content. LFZ processing under a hydrogen-containing atmosphere was found to promote the reduction of titanium cations and inducing oxygen deficiency, as confirmed by thermogravimetric analysis. This reduction significantly enhanced the electrical properties of the samples. The thermoelectric properties were evaluated by measuring the Seebeck coefficient and electrical conductivity at high temperatures. The electrical performance was found to be sensitive to both Ta content and specific microstructural features, including the presence of Magneli phases. A maximum power factor of 735 mu W/(m center dot K2) was achieved at 1120 K, which is one of the best values reported in the literature for similar materials.

keywords

RAMAN-SPECTRA; PHASE-TRANSFORMATION; DOPED TIO2; PERFORMANCE; SPECTROSCOPY; CERAMICS; RUTILE

subject category

Materials Science

authors

Lopes, D; Kovalevsky, A; Yaremchenko, AA; Mikhalev, SM; Costa, FM; Ferreira, NM

Groups

G3 - Electrochemical Materials, Interfaces and Coatings

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

Collaboratory for Emerging Technologies, CoLab (EMERGING TECHNOLOGIES)

acknowledgements

This work was developed within the scope of the project i3N, LA/P/0037/2020, UIDB/50025/2020 & UIDP/50025/2020, financed by national funds through the FCT/MEC. The authors also acknowledge the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI 10.54499/UIDB/50011/2020) , UIDP/50011/2020 (DOI 10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI 10.54499/LA/P/0006/2020) , financed by "National Funds through the FCT/MCTES" (PIDDAC) . Diogo Lopes acknowledges the Ph.D. scholarship by FCT (grant https://doi.org/10.54499/2020.06454.BD) . This work was also funded by national funds (OE) , through FCT - Fundacao para a Ciencia e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. The authors are thankful to Iolanda Fortes for her valuable contributions to the experimental work.