Crystal grain size dependence of thermoelectric properties for sintered PbTe by spark plasma sintering technique

Thermal and electrical conduction parameters of the sintered PbTe with different crystal grain sizes Ds were measured over the temperature range from 77 to 350 K, to examine the possibility of improvement in thermoelectric performance for sintered PbTe by reducing D. The starting powders with particle sizes of 6, 39, 180 and 380 μm were obtained by pulverizing an undoped PbTe boule prepared by the Bridgman method. Sintering was carried out by the spark plasma sintering technique (SPS) under the conditions of sintering temperature of 732-803 K, sintering duration of 60-90 min and sintering pressure of 45 MPa. All the sintered compacts, whose conduction type was p-type, had an apparent relative density of more than 99%. Thermal conductivity κ decreased with reducing D below 200 K, but showed no dependence on D above 200 K. Long-wave phonons are scattered efficiently at grain boundaries only below 200 K. Hall mobility μ_H of the sintered compacts with different Ds were almost same above 200 K. It is concluded that thermoelectric performance for sintered PbTe is not directly affected by controlling D