Synthesis of highly crystalline Bi2Te3 nanotubes and their enhanced thermoelectric properties

Highly crystalline Bi2Te3 nanotubes are fabricated on a large scale by a facile one-pot hydrothermal method. In our synthesis, single crystal Te nanorods form first as not only the intermediate but also the sacrificed template, which enables the epitaxial growth of the Bi2Te3 crystal on the Te template along the c-axis. Surfactant poly(vinyl pyrrolidone) is employed as the diffusion barrier to adjust the diffusion rate of different elements and to control the growth rate, leading to the highly crystalline hollow structures of Bi2Te3 nanotubes with improved morphology. Bulk materials for thermoelectric property investigation have been obtained by spark plasma sintering which largely preserves the nanoscale size and hollow nature of Bi2Te3 nanotubes. The unique holey nanostructures with a porosity of about 20% and a nanoscale crystal size result in greatly enhanced phonon scattering, and therefore the thermal conductivity is dramatically decreased. However, the holey nanostructures of the bulk sample have small effects on the electrical properties, which might be ascribed to the highly crystalline nature of Bi2Te3 nanotubes. Finally, a reduced thermal conductivity around 0.62 W m(-1) K-1, a comparable power factor of 10.3 mu W cm(-1) K-2, and a significantly increased ZT value of 0.77 are achieved at 464 K, which demonstrates the promising potential to further promote the thermoelectric properties of bulk materials through holey nanostructures.