ThermoEMF of powder-based thermoelectric materials

TL;DR

This paper models the thermoEMF of powder-based thermoelectric materials, showing how particle size and scattering index influence thermoEMF, and discusses conditions for potential enhancement over single-crystal materials.

Contribution

It introduces a theoretical calculation of thermoEMF considering power dependence of mean free path, highlighting conditions for increased thermoelectric efficiency in powder materials.

Findings

ThermoEMF decreases with larger particle radius.

Higher scattering index can lead to greater thermoEMF than single crystals.

Experimental results show no significant increase in thermoEMF from powders due to lack of energy filtering.

Abstract

In the paper, the thermoEMF of powder-based thermoelectric materials (TEM) is calculated. The calculation is made on the assumption of power dependence of mean free path on energy. The thermoEMF decreases with increasing the average radius of powder particles, however, it drastically increases with an increase in power exponent in the law of dependence of the mean free path of relaxation time on energy (scattering index). Therefore, it turns out that the thermoEMF of powder-based TEM with a higher scattering index can be even greater than the thermoEMF of a single-crystal material with a low scattering index. As a consequence, a significant increase in the thermoEMF and, hence, in the thermoelectric figure of merit of TEM in going to powder materials, especially in the case of degenerate electron gas, can be expected only if dielectric or vacuum barriers between powder particles do not lead to a significant decrease in electrical conductivity. At the same time, tunnelling through the abovementioned barriers should provide such an energy filtration of charge carriers, which leads both to an increase in the proportion of "useful" charge carriers with energy greater than the chemical potential, and to an increase in the scattering index. However, experimentally, there is no significant increase in thermoEMF in going from single-crystal materials to powders, most likely because such energy filtering does not take place.