Thermoelectric properties of the compounds AgPb_mLaTe _m+2

The thermoelectric properties of the new compounds AgPb_m LaTe_m+2(m = 15, 18, 20, 25, 30, 35) were investigated in the temperature range of 300 to ∼720 K and compared to those of AgPb ₁₈MTe₂₀ (M = Sb, Bi). All samples crystallize in the NaCl-type structure without noticeable secondary phase. The room-temperature electrical conductivities of the AgPb_mLaTe_m+2 samples are > 1700 S/cm, which are higher than the Sb or Bi analog. The Seebeck coefficient in the AgPb_mLaTe_m+2 samples ranges from -60μV/K at 300 K to -160μV/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 AgPb_mLaTe _m+2 samples. The corresponding power factors (15-17 μW/ (cm K ²) at ∼670 K) of the AgPb_mLaTe_m+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 AgPb_mLaTe_m+2 samples are < 1.4 W/(m K), which are higher than that of the Sb analog (∼0.8 W/(m K)) and are comparable to that of the Bi analog (∼1.2 W/(m K)). A ZT of ∼0.9 at ∼670 K was achieved for the AgPb₂₅LaTe₂₇.