  Theoretical analysis of the effect of thermoelectric phenomena on the
relation of effective electrical and thermal conductivity in the
macroscopically inhomogeneous media is carried out. Plane-layered structures,
two-dimensional self-dual and three-dimensional randomly inhomogeneous media
are examined. It is shown that the relation of effective electrical to thermal
conductivity, which is independent of concentration in so-called
Wiedemann-Franz media, in the case of high values of internal thermoelectric
figure of merit can be considerably different from the one for the local values
in each phase. The decrease of the relation may have negative impact on the
effective figure of merit of composites and thus lead to the decrease of
thermoelectric devices efficiency.
