Evaluation of thermoelectric properties of impurity-doped PbTe

PbTe single crystals were prepared by the Bridgman method, where either Ag2Te or PbI2 was doped as the source material of silver and iodine. The hole concentration was successfully controlled in the range from 2.0 x 10(24) to 9.0 x 10(24) m(-3) by doping 100 to 700 mol ppm Ag2Te, and from 3.5 x 10(23) to 4.5 x 10(24) m(-3) by doping 100 to 650 mol ppm PbI2. In the case of PbI2 doping, the conduction type was changed at about 700 mol ppm PbI2, and the electron concentration was controlled in the range from 5.0 x 10(22) to 5.0 x 10(25) m(-3) by doping 700 to 6000 mol ppm. Scattering factor r was estimated for both p- and n-type PbTe from the temperature dependence of Hall mobility. Thermal conductivity was calculated in terms of carrier concentration by evaluating the lattice (kappa(ph)) and electronic (kappa(el)) thermal conductivities. The kappa(el) was estimated on the basis of Fermi integral by using observed data of alpha and r, where the kappa(ph) was estimated to be 2.15 Wm(-1) K-1 using the calculated kappa(el) value and the literature kappa data for undoped PbTe. Maximum figure-of-merits (Z(max)) of PbTe at 300 K were 1.21x10(-3) K-1 for the n-type at n = 2.76 x 10(24) m(-3) (2000 mol ppm PbI2) and 1.38 x 10(-3) K-1 for p-type at p = 2.34 x 10(24) m(-3) (200 mol ppm Ag2Te).