Enhancement of thermoelectric properties in liquid-phase sintered Te-excess bismuth antimony tellurides prepared by hot-press sintering

Abstract Various approaches have been applied to improve the thermoelectric performance of bismuth antimony telluride based materials. Here, we prepare the bulk pellets of nominal Te-excess p-type Bi0.4Sb1.6Te3+x (x = 0, 0.2, 0.4, 0.6, 0.8, 1) samples by a high-temperature solid state reaction followed by a hot-press sintering, and performe structural investigations including X-ray diffraction measurements and a high-resolution transmission electron microscopy analysis as well as a thermoelectric property characterization including electrical resistivity, Seebeck coefficient, thermal conductivity, and Hall effect. We demonstrate that a liquid-phase sintering of Te-excess samples can provide a preferential orientation of a bulk pellet along a measured direction, an improvement in hole carrier concentration, and sub-micron sized Sb precipitates acting as a phonon scattering center, resulting in an enhancement in power factor and a reduction in lattice thermal conductivity compared to the pristine x = 0 sample. Consequently, the hot-pressed bulk pellet of the nominal Bi0.4Sb1.6Te3.4 composition exhibits an impressively high ZT of 1.41 at 417 K along the vertical direction, which is about 31 % enhancement in ZT compared to the pristine Bi0.4Sb1.6Te3 sample. The significantly improved values of practical thermoelectric properties such as engineering (ZT)eng, maximum efficiency ηmax, and output power density Pd indicates a practical applicability in thermoelectric energy harvesting technologies.