OPTIMIZATION OF Bi₂Te_3-xSe_x ALLOYS VIA DOPING FOR THERMOELECTRIC POWER GENERATION APPLICATIONS

The rising awareness of the global warming effect as well as the steady decline in the quantity of current resources and subsequently the climb in their price drive the search for improving current energy usage and finding new energy resources. Thermoelectric devices take thermal heat, either directly from solar energy or as a byproduct of fuel burn, and transform it to electricity.

The performance of thermoelectric devices is assessed by the dimensionless figure of merit ZT of the material, defined as ZT =α²σT/k, where α, σ, k and T are the Seebeck coefficient, the electrical and thermal conductivities, and the absolute temperature, respectively. The thermal conductivity is a combination of thermal conductivity via electrons, κ_e, and via phonons, κ_l. The main difficulty in improvement of the efficiency of a thermoelectric device is due to the complex relation between σ, α and k. Improving the performance of thermoelectric materials is usually done either by improving the power factor, α²σ, or by applying phonon scattering methods in order to lower the thermal conductivity.

Bismuth–telluride-based alloys are of great importance not only as the best thermoelectric materials with the maximal ZT values close to unity near room temperature, but also due to the potential for further performance improvement.

In this study Bi2Te_3-xSe_x compositions were electronically optimized by various CHI₃ doping levels, preferred alignment of the crystallographic orientation, and lattice thermal conductivity minimization. The synthesis route included rocking furnace melting, energetic ball milling and hot pressing under optimal conditions for enhancement of the thermoelectric figure of merit, ZT commonly applied in low temperature power generation applications. The transport properties in perpendicular to the pressing direction were examined.