Structure evaluation of bismuth telluride (Bi2Te3) nanoparticles with enhanced Seebeck coefficient and low thermal conductivity

Bismuth telluride (Bi2Te3) nanoparticles with different morphologies were synthesized using solvothermal process. The composition, the size and the micro-structure of the synthesized nanoparticles were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). Band gap energy was determined using UV-vis spectrometer. The absorption peaks were shifted from 278 to 284 nm which confirm that the effect of the size and the nanostructure morphology. Moreover, the direct band gap (E g ) of ST–Bi2Te3, STEd–Bi2Te3, STNaEd–Bi2Te3, STPv–Bi2Te3 and STNaPv–Bi2Te3 were equal to 3.95,4.7,4.8,4.7 and 4.5 eV. Thermal and electrical conductivity of the prepared nanoparticles were also investigated at room temperature. Plainly, thermal conductivity measurement concludes that thermal conductivity of ST–Bi2Te3 sample prepared without any additives was high. The study revealed that, the addition of NaOH to the reaction medium as an alkali modifier has a great effect on the morphology and the size of the produced nanoparticles. The additions of PVP in absence and in presence of NaOH strongly affect the size and the morphology of the product. The effect of changing the morphology and the particle size were determined on the band gap energy and the Seebeck coefficient of the prepared samples and the negative sign of all Seebeck coefficients indicate n-type semiconductor.