Preparation And Properties Of BiFeO 3 -based Multiferroic Materials

BiFeO3 is a typical single-phase multiferroic which has the ability to possess ferroelectric order and ferromagnetic order simultaneously at room temperature.It exhibits a special magnetoeletric coupling and considered to have potential application value in future information technology and microelectronic devices.BiFeO3 powders were synthessized by chemical coprecipitation method,and then the bulk BiFeO3 ceramics were prepared by a sintering technology of spark plasma sintering(SPS).In order to investigate the doping effect on phase composition and properties of BiFeO3 ceramics,Bi1-xLaxFeO3(x=0,0.05,0.10,0.15,0.20 and 0.30)were prepared by solid state reation,and BiFe1-xTixO3(x=0,0.05,0.10 and 0.15)were prepared by solid state reation.The dielectric,ferroelectric,ferromagnetic and leakage current properties of ceramics were studied systematically.The powders were synthesized by different synthesis condition and then were studied by means of XRD.The optimum synthesis system were determined,the pH value is kept around 12,the co-precipation reaction is 47h,the Bi-Fe nitrate solution is precipitation is prepared with Bi excessing 3%,the synthesized powers is calcined at 600? for 2 h.Scanning Electron Microscope(SEM)results show that the particle size distribution of BiFeO3 powders is about 100nm.The magenetic properties of powders synthesized by different condition indicate only the single-phase powers show the weak ferromagnetic.The phase analysis of SPS ceramics indicate BiFeO3 ceramics decomposes into Bi25FeO40 and Bi2Fe4O9,however the particals are very small and the particle size distribution is about 300?500nm.The dielectric proterites displays Debye-type behavior.The leakage current density curves indicate the samples have increased leakage current.The form of ferroelectric hysteresis loop present circle and the ceramics sample show poor ferroelectric properties.Compare with powders,the ceramic samples show larger magnetization and improved ferromagnetic properties.The La substitution of BiFeO3 ceramics were prepared by solid state reation at 800?.The effect of La substitution amount on the crystal structure,dielectric and multiferroic properties of the ceramics was investigated.The results indicate that single-phase Bi1-xLaxFeO3(x=0.15)ceramics is prepared.With an increase of La content,a structural changes evolutes from rhombohedral to tetragonal structure Due to the controled cycloid spin structure caused by the changes in the crystalline structure,the Bi1-xLaxFeO3(x=0.30)ceramics possess enhenced ferromagnetic moment.The dielectric constant increases until maximum and then decreases with an increase of La content,under a frequency of 106Hz.The dielectric loss of La-modified BiFeO3 ceramics is raised compared with BiFeO3 ceramics.The reduction of leakage current density rather than ferroelectric structural distortion enhances the ferroelectric properties of La-modified BiFeO3 ceramics.The Ti substitution of BiFeO3 ceramics were prepared by solid state reation at 860?.With an increase of Ti content,the structural changes evolutes from rhombohedral to orthorhombic structure,the average grain sizes of BiFeO3 ceramics decreased simultaneously.The dielectric constant increases until maximum and then decreases with an increase of La content,under a frequency of 106Hz.The dielectric loss of Ti-modified BiFeO3 ceramics is raised compared with BiFeO3 ceramics.The leakage current density of samples is decreasing gradually.Under a voltage of 100V,the leakage current density of BiFe0.85Ti0,15O3 ceramics is 1.07×10-8A/cm2,it is weaker than undoped ceramics about 2 orders of magnitude.The Ti substitution of BiFeO3 ceramics show improved ferroelectric properties.