On the Synthesis, Microstructure, and Thermoelectric Properties of the Composite Material Bi₂Te_2.7Se_0.3/Te_δ Obtained from Asymmetric Nanoparticles

Composite materials Bi₂Te_2.7Se_0.3/Te_δ with varying concentration (δ = 0.15, 0.2, 0.25, and 0.3) are obtained by the solvothermal synthesis of initial powders and their subsequent spark plasma sintering. During the sintering process, the samples are textured, as a result of which lamellar grains are arranged in layers perpendicular to the direction of the application of pressure during sintering (the direction of the texture axis). Upon magnification, the concentration of superstoichiometric tellurium decreases the degree of texturing. The concentration of tellurium does not affect the average grain size. Superstoichiometric tellurium is distributed along the grain boundaries, as a result of which a structure characteristic of composite materials is formed. The release of tellurium at the grain boundaries leads to a change in the thermoelectric properties of the obtained materials. The electrical resistivity naturally increases, and the total thermal conductivity decreases with an increase in the concentration of superstoichiometric tellurium.