CORRELATING MICROSTRUCTURAL EVOLUTION WITH THERMOELECTRIC PROPERTIES OF SILVER-ANTIMONY-TELLURIUM-BASED COMPOUNDS

Pronounced Seebeck effect in thermoelectric (TE) materials allows the direct conversion of heat into electric power. This may contribute to global efforts of developing renewable energy sources. Achieving superior TE performance requires not only optimal TE properties but also thermal stability of microstructure at elevated temperatures. We study the temporal evolution of microstructure of the promising Ag-Sb-Te (AST)-based TE materials by conducting aging heat treatments at several temperatures and correlating microstructural parameters with TE properties.

Aging of an Ag_16.7Sb₃₀Te_53.7 compound at 380 °C induces nucleation of Sb₈Te₃ precipitates in the form of long plate geometry that are fully coherent with the AST-matrix, and have the Sb₈Te₃AST orientation relationship. We classify these precipitates into two populations according to their thickness: one on the sub- 100 nm size, and the other on the micrometer length scale. The maximum thickness follows a parabolic growth rate between 2 and 8 h aging, yielding an interdiffusion coefficient of the order of 10^-18 m²s^-1.

While the lattice thermal conductivity drops by about 37% and the electrical conductivity increases by a factor of 2, the Seebeck coefficient is found to decrease by 16% leading to an overall enhancement of the dimensionless TE figure of merit by a factor of 2 upon dwell for 8 h at 380 °C. These trends reasonably correlate with the reduction in the degree of matrix supersaturation occurring during the initial precipitation stages at t < 8 h.

We elucidate the complex influence of microstructural evolution in AST-based alloys on their TE properties. This is expected to pave the way for tailoring the TE properties of AST via materials processing techniques.