Magnetoelectric Coupling Performance Of Potassium Sodium Niobate-cobalt Ferrite Ceramics

With the rapid development of science and technology and cross-penetrationbetween the various science, the demand for miniaturized devices increasescontinually. While, traditional materials with single performance have difficulty insatisfying people’s various high demands for the material properties. Thus, we needto develop a new type of materials with two or more functions.Multiferroicmaterials possess both ferroelectric and ferromagnetic properties.The couplinginteraction between them indicates its potential application in modern technology,which can create unprecedented economic benefits. In recent years, potassiumsodium niobate (KNN) based lead-free piezoelectric ceramics have become one ofthe most promising candidates, for their excellent piezoelectric, ferroelectricproperties, and high Curie temperature. For ferromagnets, the spinel-type cobaltferrite materials (CoFe2O4) have got a lot of attention because of their largemagnetostrictive effect. Based on this, ferromagnetic material CoFe2O4was dopedinto KNN, and we researched the magnetoelectric coupling effect between these twomaterials.In this thesis, KNN-CoFe2O4multiferroic ceramics were prepared byconventional solid-state reaction method firstly. The phase structure of pure andCoFe2O4-doped KNN ceramics were analyzed by Using X-ray diffraction method.This also was used to conclude that whether these two-phases still coexisted, andwhether impurity was formed or not. The microstructure of KNN-CoFe2O4ceramicswas studied by using scanning electron microscopy (SEM).The sinteringcharacteristics, such as the distribution of grains, porosity and compactness, werealso studied. The effectof CoFe2O4dopingon the KNN was further discussed.The dielectric properties of KNN-CoFe2O4multiferroic ceramics were studied.The effect of CoFe2O4on the phase transition and the dielectric loss was analysized.Quasi-static piezoelectric coefficient d33was measured. The ratio dependence of d33was studied combining the sintering behavior.Ferroelectric hysteresis loops and magnetic hysteresis loops of KNN-CoFe2O4multiferroic ceramics were measured. This result proved the coexistence offerromagnetic and ferroelectric phases in samples. Then, the magnetoelectriccoupling effect was characterized by measuring the magnetocapacitance.Theoptimum doping ratio wasalso determined. At last, basic physical mechanism ofmagnetoelectric coupling effect was analysized.