TiO₂-SrTiO₃ Biphase Nanoceramics as Advanced Thermoelectric Materials

The review embraces a number of research papers concerning the fabrication of oxide thermoelectric systems, with TiO₂-SrTiO₃ biphase ceramics being emphasized. The ceramics is particularly known for a two-dimensional electron gas (2DEG) forming spontaneously on the TiO₂/SrTiO₃ heterointerface (modulation doping), unlike ordinary 2DEG occurrence on specially fabricated thin film. Such effect is provided by the SrTiO₃ conduction band edge being 0.40 and 0.20 eV higher than that for anatase and rutile TiO₂, respectively. That is why, in the case of a checkered arrangement of TiO₂ and SrTiO₃ grains, the united 2D net is probably formed along the grain boundaries with 2DEG occurring there. To reach such conditions, there should be applied novelties in the field of ceramics materials science, because it is important to obtain highly dense material preserving small (nanoscale) grain size and thin interface boundary. The review also discusses some aspects of reactive spark plasma sintering as a promising method of preparing perovskite-oxide TiO₂-SrTiO₃ thermoelectric materials for high-temperature applications.