Formation and thermoelectric property of TiO2 nanotubes covered by Te–Bi–Pb nanoparticles

A variety of strategies have been attempted to improve the performance of thermoelectric materials. The primary approach is to employ low-dimensional materials to reduce the lattice thermal conductivity as described by the Wiedemann–Franz law. That is, to decrease the thermal conductivity, rattling structures, point defects, vacancies and nanocomposites have been used to efficiently scatter phonons within or between the unit cell crystals. Complex crystalline structures have been used to decouple the electrical conductivity and thermal conductivity to achieve this goal. Based on such considerations, we have prepared TiO₂ nanotubes from titanium foils. These nanotubes are low-dimensional, thus, preferable to achieve low lattice thermal conductivity to generate favorable thermoelectric properties. Moreover, scattered Te–Bi–Pb nanoparticles have been deposited on the surface of the TiO₂ nanotubes via electrochemical method. The purpose of the nanoparticles is to further enhance the performance of the thermoelectricity, specifically in our case, to increase the Seebeck coefficient. From the results obtained, the best Seebeck coefficient for pure TiO₂ nanotubes is about 90 μV/K; while the best Seebeck coefficient for TiO₂ nanotubes covered with scattered Te–Bi–Pb nanoparticles is about 155 μV/K. This significant improvement could be explained by the quantum confinement in such a peculiar nanostructure.