Roles of AgSbTe2 nanostructures in PbTe: controlling thermal properties of chalcogenides

Abstract

In this study, we report on the formation behavior of homogeneous nanostructures and the thermal properties of quaternary system AgPb_mSbTe_m+2 (silver- and antimony-doped PbTe, m = 18) that were synthesized via nanostructure crystallization engineering by controlling thermal processes. It is well known that with the addition of excess amounts of Ag and Sb into a PbTe system, nano-grained structures can be dispersed in the matrix of grains or segregated as clusters at the grain boundary of PbTe. Here, we observed the nanostructures with grain size ranging from 1 nm to 15 nm, which were synthesized under consecutive thermal procedures. They were examined by elaborated transmission electron microscopy. For thermal conductivity, the reduction rate was 20–30%, which mainly originated from decrease of the lattice thermal conductivity due to crystal phonon scattering (lattice vibrations) from formation of AgSbTe₂ nanostructures in the PbTe grains. The lattice thermal conductivities of the entire system, with controlled AgSbTe₂ nanostructures in PbTe matrix, are substantially lower than in other cases. Finally, the best thermal conductivity reduction rate is shown in AgPb₁₈SbTe₂₀ compound heat-treated at 923 K. As a result, these nano-grained PbTe materials could be expected to increase ZT from thermal conductivity reduction.