Mr. Meir Haim Dahan, M.Sc. Candidate
Department of Materials Science and Engineering
Technion – Israel Institute of Technology
Haifa 3200003, Israel
Thermoelectric (TE) devices attract extensive interest due to their ability to convert heat into electrical energy, with prime technological applications. Formation of nanometer-size features affects the transport properties of electrons and phonons in TE materials, which determine the energy conversion efficiency of the device. PbTe-based compounds establish an important class of TE materials due to their relatively high efficiency at the mid-temperature range (600-800 K). The Pb-Te-Ag system is of special interest due to its potential of forming Ag-rich precipitates dispersed in the PbTe-matrix. Investigation of the microstructure evolution of this system enables us to predict the applicability regime of this system in service temperatures, and this involves both thermodynamic and kinetic aspects. Herein, we apply first-principles calculations, implementing the transition state theory (TST), to evaluate the diffusion coefficients of silver atoms in a PbTe lattice. We determine the activation energy for diffusion and the pre-exponential diffusion coefficient for an interstitial mechanism to be ca. 10-9 m2⸱s-1 and 52.9 kJ⸱mole-1, respectively. These values are compared with experimental data collected in our TE Materials Research Group, indicating that the characteristic times required for significant microstructure evolution in these compounds can be as short as 10 min. under service conditions. This study provides us with predictive information on the thermal stability of PbTe-based compounds, thereby evaluating the kinetics of phase transformations in these compounds.