Reduced thermal conductivity in Pb-alloyed AgSbTe ₂ thermoelectric materials

Pb-alloyed AgSbTe ₂ (Pb _xAg ₂₀Sb _30-xTe ₅₀ (x = 3, 4, 5 and 6)) composites were synthesized using a modified Bridgman method with a graphite mold to form plate-like samples. The Bridgman-grown specimens were dense, with few solidification cavities, and were sufficiently mechanically robust for a variety of electronic/thermal transport measurements. Inhomogeneity was found on the grain boundary, and was embedded with the nanoprecipitates of δ-Sb ₂Te with a feature size of 100 nm of the 5 at.% Pb and 6 at.% Pb specimens. A combined effect of alloying, inhomogeneity and nanoprecipitates leads to a low thermal conductivity of 0.3-0.4 W m ^-1 K ^-1, which approaches the theoretical minimum thermal conductivity of the amorphous material (κ _min ∼ 0.36 W m ^-1 K ^-1). A peak of the zT value, ranging from 0.7 to 0.8, is achieved at 425 K. Further annealing at 673 K increases the grain size and causes a reduction in the value of the zT peak to 0.4.