Synthesis And Properties Of Ni_1-xZn_xFe₂O₄-Sr_1-xCa_xTiO₃Composite Ceramics

Multiferroic materials are at least two of the following behaviors in the structure. Introduction summarizes the development, classification and research status of multiferroic materials. Curie temperature of a single multiferroic materials is low, which makes it unable to be applied to devices. Multiferroic composites have been studied widely. In the paper, composite ceramics were prepared using Ni1-xZnxFe2O4and Sr1-xCaxTiO3as ferromagnetic and ferroelectric, respectively. The phase formation, microstructure, dielectric properties, ferroelectric and ferromagnetic properties were investigated. The paper main content is as follows:1. xNio.5Zno.5Fe204-(1-x)CaTi03(0≤x≤1.0) composite ceramics, which have high density and uniform grain size distribution, were synthesized at1260℃for3h. The dielectric constant of composite ceramics decrease with the increase of frequency, and finally is constant. The dielectric constant of composite ceramics increases and loss tangent decreases with the increase of Nio.5Zn0.5Fe2O4content since the dielectric constant of Nio.5Zno.5FeO4is higher than that of CaTiO3.0.7Nio.5Zno.5Fe2O4-0.3CaTO3composite ceramic has ferroelectric property, but high leakage current. Comosite ceramics have typical magnetic hysteresis loops, which saturates in the a(?)lied magnetic field. The saturation magnetization of the composite ceramics inc(?)ses with the Ni0.5Zno.5Fe2O4increasing, which can be attributed that the mag(?)ic property of the composite ceramics is form Nio.5Zn0.5Fe2O4. The satu(?)on magnetization and coercivity of the composite ceramics are49.07emu/g and6.8Oe, respectively.2. xNiFe2O4-(1-x)SrTiO3(0.1≤x≤0.5) composite ceramics, which have high uniform grain size distribution, were prepared by conventional ceramic sintering and m(?)rowave sintering, respectively. The dielectric constant and loss tangent of xNiFe2O4-(1-x)SrTiO3(0.1≤x≤0.5) composite ceramics both increase as the frequency increasing, and finally tend to be constant, which is similar to the Koops phenomenological theory. In comparison, the dielectric constant and loss tangent by microwave sintering are both higher than that by conventional sintering. xNiFe2O4-(1-x)SrTiO3(0.1≤x≤0.5) composite ceramics have typical ferroelectric hysteresis loops, indicating the presence of ordered ferroelectric structure. The ferroelectric property of xNiFe2O4-(1-x)SrTiO3(0.1≤x≤0.5) composite ceramics increase with the increasing of the applied electric field from50V/mm to200V/mm. Composite ceramics have typical magnetic hysteresis loops. The saturation magnetization of the composite ceramics increases with the NiFe2O4increasing, which can be attributed that the magnetic property of the composite ceramics is form Nio.5Zno.5Fe204and SrTiO3is non-magnetic phase.3. Bi2O3doping0.5NiFe2O4-0.5SrTiO3composite ceramics were prepared by conventional sintering at1200℃for3h, which have high uniform grain size distribution. BiFeO3content improves with the increase of Bi2O3doping content. The dielectric constant of Bi2O3doping0.5NiFe2O4-0.5SrTiO3composite ceramics is higher than that of0.5NiFe2O4-0.5SrTiO3composite ceramic. Curie temperature of doping0.5NiFe2O4-0.5SrTiO3composite ceramics appears near220℃, indicating doping makes the Curie temperature of SrTiO3to shift to higher temperature. doping0.5NiFe2O4-0.5SrTiO3composite ceramics show typical ferroelectric hysteresis loops, and their spontaneous polarizations overmatch that of0.5NiFe2O4-0.5SrTiO3composite ceramics. Bi2O3doping0.5NiFe2O4-0.5SrTiO3composite ceramics show typical magnetic hysteresis loops. When Bi2O3doping content is0.5%, the saturation magnetization, remnant magnetization and coercivity of the composite ceramic are53.59emu/g,2.07emu/g and7.32Oe, respectively.