Synthesis And Properties Research Of The Potassium Sodium Niobate Based Lead-Free Piezoelectric Laminated Magnetoelectric Composites

With the rapid development of science and technology,the miniaturization and multifunction in the field of electronics has become an hot research topic.The magnetoelectric composites simultaneously exhibit ferroelectricity,ferromagnetism and magnetoelectric coupling performance,which possess a very broad application prospects such as sensors,filters,phase shifter,data storage ect al.However,the magnetoelectric effect of single-phase magnetoelectric materials is weak at low temperature,leading to a difficulty in practical applications,and now the currently magnetoelectric materials give priority to with magnetoelectric composites.The magnetoelectric composites are mainly divided into laminate composites and particulate composites according to the structure,and the laminate composites have attracted much attention because of their excellent magnetoelectric properties.At the same time,lead-free magnetoelectric composites are mainly based on BaTiO3-based piezoelectric materials,whose magnetoelectric coupling coefficients are relatively low.To further to enhance the magnetoelectric properties,the laminate composites with selecting the high-performance piezoelectric materials are prepared by adjusting the structure and changing the molding process.In this article,we compared their performance and investigated the factors which affect the magnetoelectric effect.The magnetoelectric effect is achieved by the product effect of the piezoelectric effect and magnetostrictive effect,not only connects closely with the performances of two signel-phases but also affected by the relatively content of two phases.In this paper,the laminate magentoelectric composites were prepared by doping modification of KNN based piezoelectric materials and?Ni,Zn?FeO₃,CoFe2_O4 based ferromagnetic materials.The X-ray diffraction?XRD?and Scannig electron microscope?SEM?were used to analyze the phase composition and structures.The ferroelectric tester was used to analyze the electrical properties.The self-assembled magnetoelectric tester was used to analyze the magnetoelectric performances.Compared with the particulate composites,laminated composites possess the superiority.First of all,(K_0.45Na_0.55)_0.98Li_0.02(Nb_0.77Ta_0.18Sb_0.05)O₃?LKNNTS?with codopants of Li,Ta and Sb and Ni_0.37Cu_0.20Zn_0.43Fe_1.92O_3.88?NCZF?were chosen as the piezoelectric phase and magnetic phase,respectively.The LKNNTS and NCZF were pressed together through the cold isostatic pressing method and then sintered to achieve the laminated LKNNTS/NCZF composites.The results show that the two phases of LKNNTS and NCZF can coexist in the composites,and there are not any chemical reactions and the obvious diffusion of element at high temperatures.In the dielectric,ferroelectric and magnetoelectric performance tests,compared with the particulate composites,the laminate composites have larger resistivities,higher Curie temperature?240 oC?,typical ferroelectric saturated hysteresis loops,lower leakage currents and excellent magnetoelectric effect.The largest magnetoelectric coefficient of the LKNNTS/NCZF laminate composites reaches up to 133 mV/cm Oe,which is approximately four times as large as that of particulate composites?34 mV/cm Oe?.Secondly,Li_0.058(Na_0.535K_0.48)_0.942NbO₃?LKNN?with simple Li-doping was chosen to be the ferroelectric phase and Co_0.6Zn_0.4Fe_1.7Mn_0.3O₄?CZFM?with the high magnetostrictive effect was used as the magnetic phase,0.3 wt% Li₂CO₃ was added into CZFM powder as sintering aids to co-fire the two phases together,and the laminated LKNN/CZFM composites prepard by the same condition of laminated LKNNTS/NCZF composites.The results show that LKNN can coexist with CZFM and no interdiffusion and chemical reactions occurs in the process of high temperatures sintering.The as-prepared LKNN/CZFM composites with lamellar structure are composed of well-developed grains,have a relatively dense microstructure and no obviously defects and porosity.The laminate structure LKNN/CZFM composites possess a better magnetoelectric effect,and the largest ME coefficient reaches up to 285 mV/cm Oe,which is the big enhancement compared with the laminated LKNNTS/NCZF composites.In order to further enhance the ME properties of the laminated composites,the multilayer LKNN/CZFM composites were prepared by the tape casting technique.The as-prepared film with the smaller size defect are distributed uniformly in the two-dimensional tape,which possess the more consistent and more stable performances.The results show the multilayer composites have high breakdown strength and excellent dielectric,piezoelectric,ferromagnetic and magnetoelectric properties due to their high resistances and low leakage currents compared with the trilayer composites.The largest ME coefficient of the multilayer LKNN/CZFM composites reaches up to 307 mV/cm Oe,which is the highest for the lead-free bulk ceramic ME composites so far.