ABSTRACT
A measure for
the efficiency of a thermoelectric material is the figure of merit defined by ZT = S2T/ρκ, where S, ρ and κ are
the electronic transport coefficients, Seebeck coefficient, electrical
resistivity and thermal conductiviy, respectively. T is the absolute temperature. Large values for ZT have been realized in nanostructured
materials such as superlattices, quantum dots, nanocomposites, and nanowires.
In order to achieve further progress, (1) a fundamental understanding of the carrier transport in
nanocomposites is necessary, and (2) effective experimental methods for designing, producing and measuring
new material compositions with nanocomposite-structures are to be applied.
During the last decades, a series of
formulas has been derived for calculation of the electronic transport
coefficients in composites and disordered alloys. Along the way, some puzzling
phenomenons have been solved as why there are simple metals with positive
thermopower? and what is
the reason for the phenomenon of the “Giant
Hall effect”? and what is the reason for the fact that amorphous
composites can exist at all? In the present review article, (1), formulas will be presented for calculation of σ = (1/ρ), κ, S, and R in composites. R, the Hall coefficient, provides additional informations about the
type of the dominant electronic carriers and their densities. It will be shown
that these formulas can also be applied successfully for calculation of S, ρ, κ and R in nanocomposites if certain conditions are taken into account. Regarding point (2) we shall show
that the combinatorial development of materials can provide unfeasible
results if applied noncritically.