Improvement of Thermoelectric Performance in Sb2Te3/Te Composites

Te-impurity-incorporated Sb2Te3, i.e., Sb2Te3 x mol % Te (x = 0, 4, 6, and 9) composites were synthesized by solid-state reaction technique. Analysis of x-ray diffraction indicates not only Te impurity as a second phase but also doping of Te via suppression of inherent Te vacancies in the Sb2Te3 matrix. As a result of this doping and of the change in formation energy of different types of native defects in Sb2Te3 due to synthesis in a Te-rich condition, carrier concentration (n(H)) lower than the pristine sample was observed. Low n(H) along with gradual convergence of valence bands due to progressive suppression of Te vacancies increases the Seebeck coefficient (S) in Te-incorporated samples. Even though Te impurities increase electrical resistivity (rho), enhanced texturing of lattice planes ensures that charge carrier mobility does not degrade due to Te addition. As a result, a maximum power factor = 17 mu W cm(-1) K-2 at T = 480 K for x = 6 has been achieved. In addition, Te addition strengthens phonon scattering via an increase of phonon-phonon Umklapp scattering and point-defect-induced scattering of phonons. Due to such a strong phonon scattering, thermal conductivity (kappa) decreases, and a reduced lattice thermal conductivity (kappa(L)), as low as 0.28 W m(-1) K-1 at 500 K for x = 6, has been achieved. As a result of simultaneous increase of S and decrease of kappa, a high ZT similar to 0.87 at 480 K, almost 33% higher than that of the host material, has been achieved.