Dielectric and impedance study of polycrystalline Li0.35-0.5XCd0.3NiXFe2.35-0.5XO4 ferrites synthesized via a citrate-gel auto combustion method

Polycrystalline ferrites having general formula Li0.35-0.5XCd0.3NiXFe2.35-0.5XO4 (0.00 <= X <= 0.08) were prepared using citrate-gel auto combustion method. Doping of Ni2+ ions in Li0.35Cd0.3Fe2.35O4 ferrite has resulted in grain growth inhibition. This has been attributed to the precipitation of Ni2+ ions in the grain boundary region during sintering process. The dielectric permittivity (epsilon'), ac conductivity (sigma(ac)) and dielectric loss tangent (tan delta) has been measured at different temperatures in the frequency domain of 100 Hz to 5 MHz. The behaviour of tan delta has been observed to show a relaxation phenomenon at relatively higher temperatures. The value of tan delta was also found to increase with temperature, which is an expected behaviour. For composition with X = 0.02, the value of dielectric permittivity was observed to increase. This is a very important feature for power applications of ferrites. Correlated barrier hopping conduction mechanism has been observed in all the samples. For sample with X = 0.00, the small polaron hopping conduction mechanism was observed first, followed by the correlated barrier hopping mechanism. The values of activation energies (E-a) for conduction process, determined from Arrhenius plots have been discussed as a function of Ni content. Nyquist plots have been utilized to delineate the contribution of the resistances of grain and grain boundary with temperature and composition. (C) 2015 Elsevier B.V. All rights reserved.