Grain size effect on thermoelectric properties of PbTe prepared by spark plasma sintering

Sintered PbTe materials with average grain sizes of 28-309 mum were prepare d by the spark plasma sintering technique. The apparent densities of the si ntered PbTe were 8.17-8.23 Mg/m(3)), which were higher than 99%, of the the oretical one. Thermoelectric properties of the sintered materials and those of the as-grown boule by Bridgman method were measured in the temperature range from 77 to 350 K. Resistivity, rho of the sintered materials increase d with decreasing grain size. Temperature dependence of rho of the sintered PbTe was remarkably different from that of the as-grown boule below 250 K because of potential barriers at grain boundaries. Hall coefficient, R-H of the sintered materials at room temperature increased from 1.4 x 10(-6) to 3.4 x 10(-6) m(3)/C, as the average grain size increased from 28 to 309 mum , which suggested that oxidation in the crystal grains was caused in the si ntering process. Temperature dependence of the thermoelectric power, alpha of the sintered PbTe below 250 K reflected the effect of carrier scattering at grain boundaries. Lattice thermal conductivity of the sintered PbTe dec reased with decreasing grain size below 250 K, while it was independent of the grain size above that temperature. Above 250 K, thermoelectric properti es of the sintered PbTe. except those in the 28 mum grain case, were consis tent with those of the as-grown boule. The values of alpha and R-H at 295 K were calculated by using a two-valence-band model involving a non-paraboli c and a parabolic valence band. The calculation results were in good agreem ent with the experimental data.