Titania embedded with nanostructured sodium titanate: Reduced thermal conductivity for thermoelectric application

Titania embedded with layer-cracking nanostructures (sodium titanate) was synthesized by a hydrothermal method and a subsequent sintering process. The structure and morphology were determined by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N ₂ adsorption-desorption experiments. In thermoelectric investigations, this nanocomposite has reduced thermal conductivity, where the minimum reaches about 2.4 W/m K at 700 C. This value is relatively low among the transition-metal oxides. Strong boundary scattering at the interfaces of the layered nanostructures and point defect scattering resulting from volatilization of Na⁺ ions seem to be main reasons for the suppression of phonon heat transfer. On the other hand, the power factor shows no apparent deterioration. Our results suggest that introduction of proper layer-cracking nanostructures into thermoelectric hosts might be effective to enhance their performance.