Thermoelectric metal tellurides with nanotubular structures synthesized by the Kirkendall effect and their reduced thermal conductivities
Polycrystalline nanotubular Bi2Te3 and PbTe were synthesized through a high-temperature solution process using extracted metal-TOPO (trioctylphosphine oxide) precursors and Te nanowires as sacrificial templates. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and high-resolution transmission electron microscopy were employed to characterize the products. The formation of such a tubular nanostructure is proposed to be the result of the Kirkendall effect. Compared with single crystalline nanotubes, such a polycrystalline nanotubular structure is considered to have great influences on the thermal conductivity owing to the numerous grain boundaries. Transport properties of hot-pressed bulk samples formed by the as-prepared nanotubular products were investigated. Thermal conductivities of the hot-pressed nanotubular samples were greatly reduced by around 80%, compared to the melt ones.