Improved thermoelectric performance of nanostructured Bi2Te3 fabricated by solvent-free mechanical alloying

Abstract

Thermoelectric materials convert waste heat energy efficiently to electricity in an eco-friendly manner. Bi2Te3 is a known thermoelectric material, which can convert waste heat and solar energy into electricity in the 200–400 K temperature range. Bi2Te3 nanocrystals are prepared in powder form by solvent-free mechanical alloying of elemental Bi and Te powder mixtures under an inert Ar atmosphere. The crystallite size and composition of the Bi2Te3 nanocrystals are analyzed using X-ray diffraction, field-emission scanning electron microscope and energy-dispersive X-ray spectroscopy. Thermal and electrical behaviours and the effect of thermal annealing are studied on the 10 h ball-milled sample in a physical properties measurement system in the 30–375 K temperature range. It is observed that the high-temperature thermal annealing induces significant grain growth, reduces lattice strain, along with a reduction of bandgap energy of the mechanically alloyed Bi2Te3 nanostructures. Thermoelectric properties and the figure of merit of the nanostructures have improved significantly upon thermal annealing. Enhanced thermoelectric performance of the annealed nanostructures has been explained considering the change in their thermal conductivity, electrical resistivity, and crystallite size induced by thermal treatment.