Understanding of intriguing metal to semiconductor transition in Ni0.5Zn0.5Fe2O4 nanoparticulates

Abstract

Temperature-dependent electrical transport characteristics of un-milled and high-energy ball-milled samples (3 h (70 nm), 6 h (55 nm) and 9 h (45 mm)) of Ni0.5Zn0.5Fe2O4 spinel ferrite were explored. A well-defined metal to semiconductor transition exhibited by all the samples has been construed in view of direct and superexchange cationic interactions and delocalization to localization of charge carriers on increasing temperature. The peak temperature (Tmax) was found to shift towards a higher temperature side on milling principally governs by the lattice vibration scattering and intrinsic excitation. The crystallite size reduction, enhancement in strain and sudden decrease in the formation and octahedral site occupancy of Fe 2+ ions on milling found responsible for the prodigious rise (~ 250 times) in normalized resistivity values for the sample comminuted for 9 h. The spectrum of energies corresponds to charge trapping centers that cause small bump (3 h milled sample) and sharp cusp (9 h milled sample) for T>Tmax. These materials may be found suitable for thermal cutoff switching applications.