Ferroelectric/ferromagnetic ceramic composite and its hybrid permittivity stemming from hopping charge and conductivity inhomogeneity

Exploring the nature of multiferroic ceramic composite with dual high performances is much important to take full advantage of its novel dielectric properties. In this paper, Ni0.5Zn0.5291Fe2O4/BaTiO3 ceramic composite is proposed and successfully prepared from BTO and NZFO powders which are obtained by sol-gel process and citric acid combustion method, respectively. Results show that with increasing BTO content from 0 to 25 vol. % in the matrix of NZFO, the permittivity of the composite decreases from 220 k to 100 k at low frequencies (similar to 40 Hz) and contrarily from 20 to 100 at high frequencies (similar to 100 MHz). It is mainly ascribed to the instant polarization in NZFO at low frequencies and the polarization in the perovskite phase of BTO at sufficiently high frequencies. The permittivity of the ferrite and composite is shown to be compatible with a hybrid model proposed, which concerns hopping charges between Fe2+ and Fe3+, conductivity heterogeneity at the grain boundaries of the ferrite, and changes in the conductivities of the two phases induced by interdiffusion of the ions between the two phases. The composition dependence of the permittivity is agreeable with Kirkpatrick's compound law with the percolation threshold of NZFO to be about 55 vol. %. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4781100]