Preparation And Multiferroic Properties Of Multi-doped Bismuth Ferrite Ceramics

The rapid development of electronic ceramic materials has made it more and more widely used in the rapid development of science and technology.Electronic ceramic materials cover a wide range of materials,including multiferroic materials.Multiferroic materials are defined as containing two or more of ferroelectric,ferromagnetic or ferroelastic properties.BiFeO₃ is a typical representative of many multiferroic materials,and its advantage is the unique single-phase multiferroic material at room temperature.The Curie temperature of BiFeO₃ T_C=1103 K and the antiferromagnetic Neel temperature T_N=643 K.In this thesis,BiFeO₃ ceramics were doped with multiple layers to increase the ferroelectric and ferromagnetic properties of BiFeO₃.The leakage current of BiFeO₃ is reduced,oxygen vacancies are reduced,and the density of ceramics is improved.The multiferroic properties of BiFeO₃ were studied by means of XRD,SEM,VSM,ferroelectric properties test and magnetic dielectric effect test.The main conclusions are as follows:?1?The pure BiFeO₃ ceramics with high purity were obtained by the comparison of different sintering methods without pre-calcining treatment and pre-firing treatment.At the same time,ceramics with higher density were obtained by pressing the ceramics at a cool pressure.?2?In the third chapter,the formula is Bi_1-xLa_xFeO₃?x=0,0.03,0.05,0.07,0.09?ceramic system,we found that La³⁺doped BiFeO₃ ceramics have the effect of suppressing the generation of heterophases,doping of La³⁺ions The crystal structure of BiFeO₃ ceramics has a certain influence,resulting in changes in the lattice parameters.When x=0.05,the dielectric loss and leakage current decrease,and the magnetic performance increases.However,the modulation structure of the spiral spins of the BiFeO₃ ceramics is still not suppressed.?3?In the fourth chapter,the ceramics were Bi_0.95La_0.05Fe_1-xTi_xO₃?x=0,0.025,0.05,0.075,0.10?ceramics.The Bi_0.95La_0.05Fe_1-xTi_xO₃ ceramic samples are all denser and have lower porosity.The average grain size is about 2⁴?m,and the grain shape tends to be consistent,which indicates that the Ti⁴⁺doping contributes to the grain Grow.When x=0.10,the dielectric constant of the ceramic sample is a maximum of 170,showing a relatively good frequency stability.The residual magnetization?Mr?increased to 0.12554 emu/g,and the saturation magnetization?Ms?increased to 0.25478 emu/g.The Ti⁴⁺doping amount was determined to be 0.05.At this time,the ceramic sample had no impurity phase and the leakage current was reduced.All the samples showed the largest magnetic dielectric effect under a 1.8 T magnetic field.When x=0.10,the?_MD was 6.34.The main reason for the analysis is that the doping of Ti⁴⁺suppresses the transition from Fe³⁺to Fe²⁺,which results in an increase in Fe²⁺and a more pronounced magnetically-enhanced magnetic dielectric effect.?4?The dielectric constant of the Bi_0.95-xLa_0.05Y_xFe_0.95Ti_0.05O₃ ceramic sample in the ceramic system of Bi_0.95-xLa_0.05Y_xFe_0.95Ti_0.05O₃?x=0,0.04,0.06,0.08,0.10?in the fifth chapter.The increase of the dielectric constant is mainly due to the doping of Y³⁺which reduces the volatilization of Bi³⁺,reduces the internal defects,and increases the dielectric constant.And the dielectric constant of Bi_0.95-xLa_0.05Y_xFe_0.95Ti_0.05O₃ ceramic samples has good frequency stability.When x=0.06,the Bi_0.95-xLa_0.05Y_xFe_0.95Ti_0.05O₃ ceramic samples obtained higher polarization and leakage current.When x=0.08,the leakage current is 10^-4 A/cm².All the samples showed the largest magnetic dielectric effect under a 1.8 T magnetic field,and the magnetic permittivity of the Bi_0.95-xLa_0.05Y_xFe_0.95Ti_0.05O₃ceramic sample gradually increased with the increase of the x content.When x=0.08,the?_MD at the 1.8 T magnetic field is a maximum of 15.64.As x increases,its magnetic permittivity?_MD increases.The reason for the analysis is that the Y³⁺doping suppresses the spin structure transformation of the BiFeO₃ceramic,significantly improves the ferromagnetic properties of the ceramic sample,and thus improves the magnetic dielectric effect.