Copper-cadmium ferrite substituted with different rare earth ions R (R=
La,Sm, Gd and Dy) are investigated. The temperature dependence of the
electrical resistivity (ρ) and thermoelectric power (α) are measured and hence
the mobility is calculated. The electrical resistivity is increased with increasing
the ionic radius of samples substituted with R = Dy, Gd and Sm while it
decreased in case La substituted sample. The thermoelectric power is found to
be temperature independent. The behavior of ρ, α and the values of the
activation energy of the resistivity Eρ support the small polaron hopping
conduction mechanism.