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

The prospects for processing Ta-substituted titanium dioxide (TiO 2 ) for thermoelectric applications were explored in this work using the Laser Floating Zone (LFZ) method under different growth atmospheres, specifically air and H 2 /N 2 . An intermediate approach, where the samples were initially LFZ-grown in air and subsequently post-annealed in H 2 /N 2 , 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 TiTa 2 O 7 to Magnéli phase-based impurities when shifting from oxidising to reducing conditions. The formation of Magnéli 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 Magnéli phases. A maximum power factor of 735 μW/(m·K²) was achieved at 1120 K, which is one of the best values reported in the literature for similar materials.