Mr. Muhamed Khalid Dawod, M.Sc. Candidate
The Auditorium, Meidan, for green pass holders, or via ZOOM
The unprecedented energy consumption each year diminishes the energy resources available in our planet. Thermoelectric (TE) technology is a promising renewable energy resource, providing direct heat-to-electricity conversion. Lead-telluride (PbTe) based TE compounds attract much attention due to their high conversion efficiency in midrange temperatures. Alloying of PbTe with silver (Ag) above its solubility limit encourages formation of second-phase precipitates, affecting electron transport and reducing the thermal conductivity by phonon scattering. Diffusion of Ag in PbTe dictates the microstructure evolution rate; particularly, precipitate nucleation, growth, and coarsening. Herein, we optimize sample preparation procedures in terms of the TE power factor (PF). We found that manually-milled specimens exhibit PF=116 𝜇W/mK2, compared to their ball-milled counterparts with PF=53 𝜇W/mK2. Remarkably, we obtained bulk density values as high as ca. 97% of the theoretical density for all samples, regardless of their processing conditions. To quantify Ag diffusion, we deposited 300 nm thick Ag layer on a PbTe substrate, followed by heat treatments. We applied secondary ion mass spectroscopy (SIMS) to analyze diffusion profiles for pure and 2 at. % Bi alloyed PbTe, from which we derived the Ag bulk diffusion coefficients, which are DAg=(5.2 ± 0.2)×10-12 and (6.8 ± 0.3)×10-12 cm2/s at 200 oC, respectively. We conclude that Bi additions do not suppress the Ag diffusion in PbTe matrix at these conditions. This information is useful to develop thermally stable PbTe-based devices.
Supervisor: Prof. Yaron Amouyal