Low field permittivity of ferroelectric-ferrite ceramic composites. Experiment and modeling

The dielectric properties of xNiFe2O4-(1-x)Pb0.988(Zr0.52Ti0.48)0.976Nb0.024O3 ceramic composites with different volume filling factors (x = 2, 5, 10, 20, 30, 40, 50, 60, 70 wt. %) prepared by sol-gel method have been investigated in the frequency range (106 ÷ 109) Hz. A reducing effective permittivity with increasing the ferrite amount was observed as result of the "sum property." The experimental results have been compared with the effective permittivity values predicted by effective medium approximation (EMA) models and finite element method (FEM) calculations. The comparison was aimed to evaluate the appropriateness of the results of the two approaches in describing the effective dielectric properties of the composite with contrasting permittivities and to understand the role of microstructural characteristics on the dielectric response in a broad filling factor range. The best description of the experimental data in overall filling factor range is given by the results of FEM calculations which used realistic microstructures and among the EMA models, by the Lichtenecker's formula.