Thermoelectric Properties of the Compounds APbmLaTem+2

The thermoelectric properties of the new compounds AgPbmLaTem+2 (m = 15, 18, 20, 25, 30, 35) were investigated in the temperature range of 300 to similar to 720 K and compared to those of AgPb18MTe20 (M = Sb, Bi). All samples crystallize in the NaCl-type structure without noticeable secondary phase. The room-temperature electrical conductivities of the AgPbmLaTem+2 samples are > 1700 S/cm, which are higher than the Sb or Bi analog. The Seebeck coefficient in the AgPbmLaTem+2 samples ranges from -60 mu V/K at 300 K to -160 mu V/K at 670 K and is Much smaller than the Sb analog, but comparable to the Bi analog. A small Seebeck coefficient is consistent with a high electron concentration of the AgPbmLaTem+2 samples. The corresponding power factors (15-17 mu W/(cm K-2) at similar to 670 K) of the AgPbmLaTem+2 samples are comparable to the Sb analog and higher than the Bi analog. The temperature dependent mobility of the La samples can be expressed through that of n-type degenerate PbTe samples. The derived room temperature lattice thermal conductivities of the AgPbmLaTem+2 samples arc < 1.4 W/(m K), which are higher than that of the Sb analog (similar to 0.8 W/(m K)) and arc comparable to that of the Bi analog (similar to 1.2 W/(m K)). A ZT of similar to 0.9 at similar to 670 K was achieved for the AgPb25LaTe27.