Effect of Mechanical Alloying on Thermal Conductivity of Bi₂Te₃-Sb₂Te₃

Abstract

A Bi₂Te₃–Sb₂Te₃ solid solution was prepared by mechanical alloying (MA) followed by hot pressing (HP). X-ray diffraction indicated that all samples which were removed at a depth below the surface of approximately 1 mm were single-phase and isotropic Bi₂Te₃–Sb₂Te₃ solid solution. Reduction of the phonon thermal conductivity as a result of the fine-grains caused by MA predominated over the solid-solution effect caused by melt growth. The Seebeck coefficient and electrical and thermal conductivities fluctuated between those for (Bi₂Te₃)_0.15(Sb₂Te₃)_0.85 and (Bi₂Te₃)_0.2(Sb₂Te₃)_0.8 at room temperature. A (Bi₂Te₃)_0.15(Sb₂Te₃)_0.85 solid solution with a dimensionless figure of merit ZT = 1.16 at 367 K was obtained by MA–HP. These results indicate that the maximum ZT of the Bi₂Te₃–Sb₂Te₃ solid solution obtained by MA–HP was not restricted to a composition of (Bi₂Te₃)_0.25(Sb₂Te₃)_0.75, which has the minimum phonon thermal conductivity in the case of melt growth.