Thermoelectric properties of fine-grained Bi₂Te₃ alloys

Fine-grained Bi₂Te₃ alloys have been prepared by a hot-pressing method using Bi₂Te₃ particles with an average particle size of 150 nm. The fine Bi₂Te₃ powders were synthesized by a hydrogen-reduction method using coprecipitation. In order to investigate the effects of phonon-grain boundary scattering, the grain size of hot-pressed alloys was controlled between 1.2 and 3.9 μ m by hot-pressing time. The Hall coefficient and the thermoelectric properties were measured in the temperature range 200-300 K. The thermoelectric properties of the hot-pressed samples were investigated from the view points of their grain size dependence and carrier concentration. It was found that the lattice thermal conductivity for an average grain size of 1.2 μ m was reduced by about 60% compared with a single crystal Bi₂Te₃ due to phonon-grain boundary scattering. Also, the grain size dependence of the thermoelectric properties was discussed.