Study On The Synthesis And Properties Of The High Temperature Lead-Free Magnetoelectric Laminate Composites

With the rapid development of science and technology, the miniaturization and micromation of the ferroelectric, dielectric and magnetic materials become an inevitable trend. Therefore, the magnetoelectric materials, which poess ferroelectric property and ferromagnetic property, may have more features on the circut in the same possession of the volume. Conversion between electronic properties and magnetic properties in magnetoelectric materials can be realized. Thus, the magnetoelectric materials are promising for applications such as sensors, transducers, filters, oscillators, phase shifter, ect al. Magnetoelectric materials consist of single-phase magnetoelectric materials and composite magnetoelectric materials. Due to poor magnetoelectric properties of single-phase magnetoelectric material, it now focus on the magnetoelectric composites. Magnetoelectric composites are divided into 0-3 type and 2-2 type composites. It is easy for 2-2 type composite materials to prepare and its magnetoelectric coupling coefficients are higher than that of the 0-3 type composite materials. At the same time, as the magnetoelectric composite are mainly put lead zirconate titanate as the piezoelectric phase, thus this paper was prepared the lead free magnetoelectric laminate composites for the environment-friendly purpose.In this paper, the ferrite bismuth based, barium titanate and sodium bismuth titanate based magnetoelectric composite materials were prepared. The comparative test methods were used to study the performance of the electrical and the magnetoelectric properties of the composites between 0-3 type and 2-2 type composites, which finally concluded the regularity of experiment results. Firstly, the solid solution BiFeO3-BaTiO3 (BFO-BT) without any other impurity phases were successful prepared and the electrical properties of BiFeO3 were improved. And then other ferrite materials like CoFe2O4 (CFO) and BiY2Fe5O12 (BYIG) were put together with it and the BFO-BT/CFO laminate composites and the BFO-BT/BYIG laminate composites were successfully prepared. At the following process the relative content of the ferromagnetic phase were changed to study the properties with the changing of the content of ferromagnetic phase. Studies have shown that, in the composite materials, BFO-BT can coexist with CFO and BYIG and there are not any chemical reactions at high temperatures, which can maintain their physical properties. In the electrical performance tests, CFO showed larger leakage current density than BYIG, therefore after preparing to composites, BFO-BT/BYIG showed a smaller value of leakage current density, a larger value of impedance and an excellent hysteresis loop than BFO-BT/CFO. However, as CFO has a large magnetostrictive coefficient, BFO-BT/CFO composite showed a larger magnetoelectric coupling coefficient. For example, compared with the 0-3 type BFO-BT/CFO composite, the 2-2 type composite showed a smaller value of dielectric loss tanS (0～1.3) than 0-3 type composite (0～3.5), a larger value of impedance (1.8×107 Ω-1.2×109 Ω) than 0-3 type composite (0.5 × 107 Ω2-4.4×108Ω) and a smaller value of leakage current density (0～300 μA/cm2) of 2-2 type composites than 0-3 type composites (0～900 μA/cm2) under the same conditions. What’s more, the hysteresis loops of 2-2 type composites were more standard than 0-3 composites under the same conditions. It also showed a larger magnetoelectric coupling coefficient of 2-2 type composites (0-27 mV/cm Oe) than 0-3 composites (0～8.6 mV/cm Oe) under the same conditions. It has similar properties in other composites.Sintering aid (LiCO3) was added into BaTiO3 (BTO) to reduce the sintering temperature of the ceramic, which would make BiY2Fe5O12 or CoFe2O4 and BaTiO3 cofired together. Using this method the BTO/CFO and BTO/BYIG magnetoelectric laminate composites have been prepared. Here the BTO-based composites exhibited a similar performance with BFO-BT-based composites, but it also showed its superiority. BTO/CFO and BTO/BYIG composites significantly improved the piezoelectric properties of the materials. The piezoelectric coefficient d33 were raised to 10 pC/N-170 pC/N and the magnetoelectric coupling coefficients of the BTO/CFO composites have reached to 135 mV/cm Oe, which is very close to the value of these international materials. In the BTO/BYIG composite materials, comparing with 0-3 type composites for 2-2 type composites, the leakage current density are reduced, the polarization performance are improved. What’s more, the magnetoelectric coupling coefficients for 2-2 type composites (4 mV/cm Oe-15 mV/cm Oe) are 60 times larger than the magnetoelectric coupling coefficients for the 0-3 type composites (0.03 mV/cm Oe-0.24 mV/cm Oe).