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The effect of nanoparticle size on thermoelectric properties of Bi 2 Te 3 nanoparticles is theoretically analysed using a phonon scattering mechanism. The size-dependent thermoelectric properties in Bi 2 Te 3 nanoparticles give an opportunity to tune the nanoparticles' size, which helps to optimize the figure of merit (ZT = S 2 σT/k). The thermoelectric effect in Bi 2 Te 3 nanoparticles is investigated using the phonon scattering effect. Reduction in nanoparticle size increases interface volume ratio, which increases the scattering of phonons with grain boundaries. An increase in phonon-grain boundary scatterings decreases the thermal conductivity (k) due to the shortening of the phonon mean free path. The Seebeck coefficient (S) and simultaneously ZT increase significantly because of a decrease in lattice thermal conductivity. The highest value of ZT = 0.45 is obtained at temperature T = 400 K for 150 nm Bi 2 Te 3 nanoparticles, which has been enhanced up to ZT = 0.92 by reducing the nanoparticles size up to 30 nm at the same temperatures. The results obtained from the present model are in good agreement with the experimental data and reflect that the thermoelectric properties are dominated by the phonon scattering mechanism and depend on the density of interfaces in the material. Numerical analysis of thermoelectric properties from the present investigation will help in designing efficient thermoelectric materials.

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