  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.
