ABSTRACT
Because of additional scattering of charge carriers on intergrain interfaces a reduction of electrical
conductivity is observed, while the thermoelectric power is affected only to a minor extent. Usually a
decrease of thermal conductivity is compensated by the decrease of electrical conductivity. Another
approach for improving the thermoelectric efficiency is by utilizing multiphase composite material,
which is also limited from theoretical point of view. Within the effective medium approximation which
is commonly used for theoretical analysis of composite materials, there is an upper bound for the
thermoelectric efficiency Z of a composite system, Z # maxðZ
Þ.
