Dielectric Dispersion in Polycrystalline Ferrites: Random Network Model

A new approach to the problem of the dielectric permittivity and losses observed in some NiZn polycrystalline ferrites which strongly differs from the Debye form is presented. Because the ferrite sample is considered as a disordered structure where the well‐conducting grains of various shape and size are separated by boundaries of low conductivity, its electric model is in the form of a large three‐dimensional network composed of either resistors with the probability p or capacitors with the probability I–p. These networks are studied by computer simulation. The resulting equivalent admittance and its standard deviation coincide very well with the experimental results obtained for a series of NiZn ferrites. It is shown that a random network model explains the “universal’dielectric behavior of ferrites at constant temperature (e.g., high dielectric permittivity at the low frequency, dielectric dispersion in the wide frequency range from 0.01 Hz to l MHz, and statistical fluctuations of the tangent of losses) due to their inhomogeneous granular structure. Random network models can be applied also to the large class of inhomogeneous dielectrics whose polarization mechanism may be explained by many‐body interactions.