Crucial role of percolation transition on the formation and electromagnetic properties of BaTiO3/Ni0.5Zn0.47Fe2O4 ceramic composites

BaTiO3/Ni0.5Zn0.47Fe2O4 ceramic composites with various compositions were sintered at different temperatures. It is found both the formation and electromagnetic properties of the composite ceramics are strongly dependent on the percolation transition of NZFO. As NZFO content x is low (x=0.1 and 0.2), the density increases with increasing the sintering temperature T from 1220 degrees C to 1300 degrees C, while it decreases as x is high (x=0.65, 0.75 and 0.85). It is ascribed to the mismatch between the densification of BTO and NZFO. Both the permeability and low-frequency permittivity of the composites exhibit typical percolation behaviors, which are appropriate to the Kirkpatrick's effective medium model with the percolation threshold f(c) ranging from 0.35 to 0.5. As x < f(c), the permeability varies little and the low-frequency permittivity decreases with increasing T, owing to the dominant control of nonmagnetic BTO and the decrease in the defects in BTO, respectively. In comparison, as x > f(c), both the permeability and permittivity increase considerably with increasing T. By analyzing the magnetic and dielectric dispersion spectra, it is revealed they are attributed respectively to the enhancement of domain-wall motion and the increase in the grain conductivity of NZFO. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.