Effect of Magnetic Phase on Structural and Multiferroic Properties of Ni1-xZnxFe2O4/BaTiO3 Composite Ceramics

Ni1-xZnxFe2O4/BaTiO3 (x=0.3, 0.4, 0.5, 0.6, and 0.7) magnetoelectric composite ceramics have been prepared by combining the coprecipitation and sol-gel methods, and their structural and multiferroic properties studied and compared. The results indicate that the synthesized composites present biphase and composite structure, with no evident impurities observed. The lattice of the Ni1-xZnxFe2O4 crystal structure is distorted owing to the incorporation of Zn2+ ions. The samples present irregular microstructure and abnormal grain growth, which can be attributed to the heterogeneous distribution of the ferroelectric and magnetic phases during preparation. The chemical composition of the larger grains is Ni1-xZnxFe2O4, while that of the smaller grains is proven to be BaTiO3. The dielectric constant of the ceramics first increases then decreases as the Zn2+ ion content is increased, which is related to the irregular microstructure of the ceramics. Both the frequency dependence of the dielectric loss and the temperature dependence of the dielectric constant present two relaxation peaks for all samples. The dielectric loss peaks are attributed to the slow polarization process, such as turning-direction and space-charge polarization, while the dielectric constant peaks can be ascribed to the ferroelectric phase transition of BaTiO3 and relaxation polarization of the composites. The abnormal magnetization behaviors can be induced by the A-B superexchange interaction caused by the addition of nonmagnetic Zn2+ ions.