Thermoelectric properties of Co₄Sb₁₂ with Bi₂Te₃ nanoinclusions

The figure of merit (zT) of a thermoelectric material can be enhanced by incorporation of nanoinclusions into bulk material. The presence of bismuth telluride (Bi₂Te₃) nanoinclusions in Co₄Sb₁₂ leads to lower phonon thermal conductivity by introducing interfaces and defects; it enhances the average zT between 300-700 K. In the current study, Bi₂Te₃ nanoparticles were dispersed into bulk Co₄Sb₁₂ by ball-milling. The bulk was fabricated by spark plasma sintering. The presence of Bi₂Te₃ dispersion in Co₄Sb₁₂ was confirmed by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron back scattered diffraction technique. Energy dispersive spectroscopy showed antimony (Sb) as an impurity phase for higher contents of Bi₂Te₃ in the sample. The Seebeck coefficient (S) and electrical conductivity (σ) were measured in the temperature range of 350-673 K. The negative value of S indicates that most of the charge carriers were electrons. A decrease in S and increase in σ with Bi₂Te₃ content are due to the increased carrier concentration, as confirmed by Hall measurement. The thermal conductivity, measured between 423-673 K, decreased due to the increased phonon scattering at interfaces. A maximum zT of 0.17 was achieved at 523 K and it did not vary much throughout the temperature range. The experimental results of composites were compared by using effective medium theories.