Preparation of sintered degenerate n-type PbTe with a small grain size and its thermoelectric properties

Sintered degenerate n-type PbTe samples with small grain sizes ranging from 0.7 to 4 μm were prepared and the effects of grain size on their thermoelectric properties were then investigated. The Seebeck coefficient of the sintered samples increased almost double when the grain size decreased from 4 to 0.7 μm. On the other hand, their electrical and thermal conductivity decreased with decreasing grain size. Accordingly, decreasing their grain size increased their thermoelectric figure-of-merit. A maximum value of the figure-of-merit of the obtained small grain-size samples was significantly higher than that of large grain-size samples with the same carrier concentration reported. This favorable result was caused mainly by the increase in the Seebeck coefficient. The influences of grain boundaries on the increase in the Seebeck coefficient were discussed. It is concluded that the Seebeck coefficient was increased by potential barrier scattering, which occurred at the grain boundaries in the sintered samples.