The Influence of R2O3 (R = Yb, Er, Dy, Tb, Gd, Sm and Ce) on the Electric and Mechanical Properties of a Nickel–Zinc Ferrite

The lattice constant, density, electrical resistivity, activation energy, carrier concentration, mobility and Vickers hardness were studied on rare-earth-substituted nickel–zinc ferrites, with formula Ni0.7Zn0.3Fe1.98R0.02O4, where R = Yb, Er, Dy, Tb, Gd, Sm and Ce. We have found that all the rare-earth ions favor the occurrence of a second phase resulting in an increase of the electrical resistivity, bulk density and hardness. The log ρ = f(1/T) curves show two regions of different activation energy. The difference between the two activation energies was explained by an important activation of the carrier mobility at higher temperatures and by a conduction mechanism sensitive to the microstructure.