Preparation And Properties Of Multiferroic Magnetic Materials, Bfo Ceramics

Multiferroics, defined as materials with coexistence of at least two of the electric, elastic, and magnetic orders, have attracted enormous research activities recently. A subsystem of multiferroics is the ferroelectromagnet, which possesses both electric and magnetic orders. The magnetoelectric effect is a combination of ferroelectric and ferromagnetic properties and is the basis of a memory device. One of the natural ferroelectromagnets is BiFeO₃, which has ferroelectric (T_C¹100K) and antiferromagnetic (T_N-640K) orders at room temperature. BiFeO₃ exhibiting both ferroelectric and ferromagnetic properties, therefore it is a material having magnetoelectric effect and is worthy of studying. BiFeO₃ has been proved to possess a rhombohedrally distorted perovskite structure at room temperature. The ferroelectrieity is caused by the shift of Bi³⁺ and Fe³⁺ off the equilibrium position compared with O^2-, and the BiFeO₃ has a spiral and antiferromagnetic spin structure.The main problems of study on BiFeO₃ can be concluded: the origin of high polarization,the relation of magnetoelectricity to structure, synthesis method is complicated and phase pure sample is difficult to obtain and so on. Conventional ceramics technique has many advantages in synthesis of ferroelectrics, such as simple device, easier composition control, and better homogeneity. It is a useful method and can be in synthesis of BiFeO₃.Single-phase BiFeO₃ and Bi_(1-x)La_xFeO₃ (X=0. 1,0.2,0.3) were prepared using Bi₂O₃ and Fe₂O₃ as precursors and La₂O₃ as additives. D/max-2550/pc x-ray diffraction instrument, which was made in Japan Rigaku Company, and Quanta 200 scanning electron microscope, which was made in Holland Philips-FEI Company, were used to show and research on microstructures, surface-structure and change orderliness of ceramics. The densities of samples in different sintering temperature were tested by XT200A digital balance, which was made in Switzerland production. The dielectric properties and piezoelectric properties were measured by ZJ-4 quasi-static d₃₃ meter, which was made in china academy of sciences, and HP4294A impedance analyzer apparatus. Correlation of properties and microstructures were analyzed and discussed, and microstructures, dielectric properties and piezoelectric properties and so on were compared among Bi_(1-x)La_xFeO₃ ceramics with different La₂O₃ addition. The main results are:1. The introduction of BiFeO₃ ceramics in preparing technologies and testing properties.2. BiFeO₃ prepared by conventional sintering method. According to TG / DTA comprehensive analysis of the results, using the traditional ceramic technology, has been with a small amount of miscellaneous BiFeO₃ of the ceramic samples, for the preparation of BiFeO₃ provide a way, this simple and easy method to study and improve the nature of BiFeO₃ provide The convenience. Through the ceramic samples from the density, SEM comparison drawn sintering optimization curve. Finally its piezoelectric constant and dielectric constant and dielectric loss was studied.3. Using the same method of preparation of the Bi_(1-x)La_xFeO₃ ceramic samples. Through the ceramic sample density, structure and morphology analysis, found that samples of pottery and not with the increase of La changes. But with the melting point of La doping increase with the increase, La doping of the increase in density makes good of its sintering temperature has also increased. XRD analysis available from La doping good inhibits the growth of the other. Finally, the 860℃sintering 2 h of the Bi_(1-x)La_xFeO_-3 piezoelectric ceramic samples performance and dielectric properties were analyzed.