The Multiferrioc Of BiFeO₃Ceramic Doping3d Transition Metals Prepared By Solid-state Reaction

With the development of electronic information technology, therequirements of device miniaturization and multi-functionalization becomehigher and higher, it has aroused extensive concern in the multiferroic withseveral functions at the same time. Multiferroic materials, which exhibit bothferroelectric and magnetic ordering, In this compound, ferroelectric polarizationand magnetization are successfully controlled by magnetic and electric fields,respectively. The coupling between these magnetic and electric degrees offreedom gives rise to potential applications in spintronic devices and sensors,BiFeO₃is the most interesting material in the family of a very few single phasemultiferroics because of its high phase transition temperature, i.e., Curietransition temperature Tc¹103K and antiferromagnetic Neel transitiontemperature TN⁶43K, It provided a train of thought to realize theminiaturization and functional of device.In order to improve the electrical and magnetic properties of BiFeO₃ceramics, we will to optimize the preparation technology and study the effect of3d transition metals substitution on the B site of BiFeO₃ceramics. The materialswill been characterized by X-ray diffraction, electronic densimeter, scanningelectron microscopy, dielectric measurements and polarization-field hysteresisloop. We will research the effect of atmospheres sintering, microwave sintering,A site and B site codoping on the purity, crystal phase composition, dielectricproperties, ferroelectroic properties and magnetic properties. The results areshown as follows:When BiFeO₃ceramics sintering in different nitrogen partial pressure. Theresults showed that the samples had hombohedra distorted perovskite structure,the density and dielectric properties of BiFeO₃ceramics improved with theincrease of the proportion of N₂in the atmospheres. When the ratio of N₂to O₂was9:1, the value dielectric loss was markedly reduced. The optimal value ofdielectric constant and dielectric loss of BiFeO₃ceramic exhibited205and0.055at5kHz, respectively. The ferroelectric hysteresis loop at room temperature wasalso measured，the result indicated that sintering in reducing atmospheres was helpful to enhance ferroelectricity and increase breakdown field. The dielectricproperties of BiFeO₃ceramics were greatly influenced by O₂and H₂atmospheres. The samples sintered in H₂atmosphere have the highest dielectricconstant. Polarization-field hysteresis loops measured at room temperatureindicted the samples sintered in H₂and N₂atmospheres have higher spontaneouspolarization and lower breakdown field.The BiFeO₃ceramics with single-phase hombohedra distorted perovskitestructure was obtained by microwave sintering. The density of the ceramics wasimproved. The dielectric loss was lower than the ceramics sintering bytraditional sintering. The dielectric property was improved. Polarization-fieldhysteresis loops measured at room temperature indicted the samples sintered bymicrowave sintering hace higher spontaneous polarization and breakdown field.The purity, crystal structures, electric properties and magnetic properties ofLa³⁺substituted BiFeO₃ceramics had been analyzed. When the doping contentx=0.15, the sample had a single-phase perovskite structure with no trace of otherimpurity phases. The density was improved. This proved that the doped of Laions could inhibited the formation of impurity, but the lattice constant waschanged by the doped of La ions, the saturated hysteresis loops was obtained, theferroelectroic properties and magnetic properties was improved when the dopingcontent x=0.15.B_i0.85La_0.15Fe_1-xMn_xO₃（x=0、0.05、0.1、0.15、0.2） was researched, when thedoped content was less than0.1, the purity phase ceramics was obtain, thedielectric properties and ferroelectroic properties was improved, the effect on themagnetic properties was quiet. When we researched the Bi_0.85La_0.15Fe_1-xCr_xO₃（x=0、0.05、0.1、0.15、0.2） ceramics, the pure phase ceramics was obtained whenthe doped content was less than0.15, the magnetic properties was improvedsignificantly.