Abstract
Sintered degenerate n-type PbTe samples with a grain size down to about 0.2 µm were prepared and their thermoelectric properties subsequently measured. Accordingly, the effects of grain size on thermoelectric properties were investigated. For samples with a grain size above ∼0.5 µm, the Seebeck coefficient and thermoelectric figure-of-merit increased with decreasing grain size. In particular, the room-temperature figure-of-merit reached a maximum value of ∼4×10-4 K-1, which is about twice as large as the value of a large-grain-size sample with the same carrier concentration reported in the literature. For samples with a grain size below ∼0.5 µm, with decreasing grain size, the Seebeck coefficient increased but the figure-of-merit did not increase because of a substantial decrease in electrical conductivity. The increase in the Seebeck coefficient with decreasing grain size was probably caused by the potential barrier scattering at grain boundaries. On the other hand, the decrease in electrical conductivity is explained mainly by the porosity effect. Thus, we consider that if a sintered PbTe sample with a smaller grain size and a lower porosity is prepared, a larger improvement in the figure-of-merit due to the potential barrier scattering can be obtained.