Microstructure, frequency and temperature-dependent dielectric properties of cobalt-substituted lithium ferrites

Ferrites with the general formula Li0.5-x/2CoxFe2.5-x/2O4 (where x = 0.1, 0 .2, 0.3, 0.4, 0.5, 0.6, 0.7) were prepared by the standard ceramic method. AC resistivity (rho(AC)), dielectric constant (epsilon') and dielectric los s tangent (tan delta) were measured as a function of frequency and temperat ure. The compositional variations of rho(DC) and epsilon' with x show inver se trends with each other. The dielectric constant increases slowly from 0 to 450 with temperature in the beginning and sharply after 200 degrees C. T he epsilon' and rho(DC) show a decrease with increase in frequency for all the samples. The variation of tan delta with frequency shows cusps for all the samples except for x = 0.5. These variations have been explained on the basis of Koop's phenomenological theory, concentration of Fe2+ and Fe3+ io ns on octahedral site and hopping frequency of electrons between Fe2+ and F e3+. (C) 2000 Published by Elsevier Science B.V. All rights reserved.