Fabrication and characterization of Ni0.3Zn0.7Fe2.0O4-BaTiO3 ceramic composites

The ceramic composites containing 1-25 vol% BaTiO3 in a ferrite matrix phase of Ni0.3Zn0.7Fe2O4 were fabricated by sintering at 1250 degrees C in air. The sintered composites indicated a steep increase in dielectric permittivity in a small BaTiO3 ratio up to 5 vol%. In a limited BaTiO3 ratio of 3-15 vol%, a reaction between Ni0.3Zn0.7Fe2O4 and BaTiO3 resulted in the production of a liquid phase during sintering, which caused correspondingly the formation of secondary phases of BaFe2O4 ss and hexagonal BaTiO3 ss. These solid phase and microstructure changes, however, brought about little contribution to the increasing permittivity of the composites. Electrical property evaluations combined with compositional analysis revealed that the remarkably increasing permittivity could be predominantly attributed to the electron hopping between Fe2+ and Fe3+ in the ferrite matrix, which was caused by the incorporation of a small amount of Ti4+ into the spinel sublattice. (C)2009 The Ceramic Society of Japan. All rights reserved.