Effects of Bi₂Se₃ nanoparticle inclusions on the microstructure and thermoelectric properties of Bi₂Te ₃-based nanocomposites

A series of thermoelectric nanocomposite samples were prepared by integrating Bi₂Se₃ nanoparticles into a bulk Bi ₂Te₃ matrix. Primarily, spherical Bi₂Se ₃ nanoparticles with diameter of ∼30 nm were synthesized by combining bismuth acetate with elemental Te in oleic acid solution. Bi2Te3-based nanocomposite samples were prepared by consolidating the appropriate quantity of Bi₂Se₃ nanoparticles with the starting elements (Bi and Te) using typical solid-state synthetic reactions. The microstructure and composition of the Bi2Te3-based nanocomposites, as well as the effects of the Bi₂Se₃ nanoparticles on their thermoelectric properties, are investigated. Transmission electron microscopy observation of the Bi2Te3-based nanocomposites reveals two types of interface between the constituent materials, i.e., coherent and incoherent, depending on the Bi ₂Se₃ concentration. The Bi₂Se₃ nanoparticles in the Bi2Te3 matrix act as scattering centers for a wider range of phonon frequencies, thereby reducing the thermal conductivity. As a result, the maximum ZT value of 0.75 is obtained for the Bi₂Te₃ nanocomposite with 10 wt.% Bi₂Se₃ nanoparticles at room temperature. It is clear that the reduction in the thermal conductivity plays a central role in the enhancement of the ZT value.