Properties Of Bismuth Ferrate Based Perovskite Multiferroic Ceramics Sintered By Microwave

Multiferroic materials have broad application prospects in high-capacity storage devices,spintronic devices,sensor devices,integrated circuits,etc.In recent years,BiFeO₃（BFO）,a single-phase multiferroic material has a special physical chemical quality,so it is widely observed and studied by the researchers.Although BFO ceramic is non-toxic,harmless and non-polluting,with a Neel temperature（370°C）and a high Curie temperature（830°C）,it is one of the few multiferroic materials with both spontaneous polarization and magnetic order above room temperature,and the calculated theoretical remanent polarization is up to 100μc/cm².However,there are some problems in the actual preparation process of this material,such as the difficulty of synthesis of pure phase and leakage conductivity,so that the bfo ceramics have the result of low dielectric and piezoelectric performance,the residual polarization is low.In addition,there are also weak magnetic properties caused by the special G-type antiferromagnetic helix structure of BFO ceramics.These problems greatly hindered the practical application of BFO ceramics.Through the continuous exploration of human beings,doping modification and process optimization are powerful measures to solve the above problems,and can improve the performance of ceramics.The doping modification of BFO ceramics can be divided into the doping of elements at sites A and B respectively and at the same time.In addition,there is a unique doping mode of forming solid solution with ABO₃ perovskite structural materials of the same type.However,in the doping modification,the BiFeO₃-BaTiO₃（BFO-BTO）solid solution ceramics have aroused people’s research upsurge due to the existence of morphotropic phase boundary（MPB）,which can improve the property of ceramics.In this paper is based on BFO-BTO solid solution ceramics,the corresponding MPB range of the matrix was first explored through the microwave sintering method in process optimization,and the corresponding performance within the MPB range was studied.Then,the same preparation method was used to doping the modified 0.7BFO-0.3BTO solution in the former base of the selected MPB.The main content of this article is as follows:（1）xBFO-（1-x）BTO（x=0.6,0.625,0.65,0.675,0.7,0.75,0.8）series ceramic samples were prepared by microwave sintering method.Firstly,the phase and micromorphology of ceramic samples were analyzed in detail.All ceramic samples showed no impurity formation.The elements have the characteristics of uniform distribution,good compactness and coarse grain,and the MPB range of x BFO-（1-x）BTO ceramics is 0.65≤x≤0.7.Subsequently,the study found that the performance of the MPB range was improved,which was consistent with the previous results of other methods.In addition,the 0.65BFO-0.35BTO ceramics in the MPB range have excellent ferroelectric properties:P_r value is 35.44μC/cm²,E_c is 50.15 k V/cm.The P_r value has reached the best level for the preparation of the matrix by traditional method,and the microwave sintering method has high quality and high preparation efficiency.It can be seen that microwave sintering method has significant advantages in the preparation of BFO-BTO based ceramics.（2）0.7BiFeO₃-0.3BaTiO₃-x%Tm₂O₃（BFO-BTO-x%Tm,x=0,0.25,0.5,0.75,1,1.5,2,2.5）series ceramic samples were prepared by microwave sintering method.The effects of biposition doping with a special location Tm on the phase structure,micromorphology,dielectric,ferroelectric and ferromagnetic properties of 0.7BFO-0.3BTO ceramic samples located in the MPB range were explored.The experimental results show that the doped samples all exhibit typical perovskite structure.With the introduction of Tm^3+,the phase of the ceramic samples changed from P4mm tetragonal phase and R3c rhombic phase to single-phase,first completely transformed into P4mm tetragonal phase and then into Pm-3m cubic phase.At the same time,the grains of all ceramic samples also decrease with the addition of Tm.The change of phase and grain will certainly bring about a series of changes in properties.Among them,the BFO-BTO-0.5%Tm ceramics with a doping amount of x=0.5 is located in the biphase region,showing excellent characteristics in other aspects except for weak ferromagnetic properties.SEM and EDS spectra show that the components have uniform distribution of elements,good compactness and large grains,and the subsequent dielectric and ferroelectric properties are also showing performance:T_m=472℃,ε_m=21586;P_r=39.22μC/cm²,E_c=53.72 k V/cm.The maximum dielectric constantε_m of the sample is about 1.61 times that of the undoped sample,and the residual polarization P_r is about 1.75times that of the undoped sample.Therefore,it can be seen that the microwave sintering method can effectively improve the electrical properties of the BFO-BTO matrix ceramics by introducing the double-occupying Tm element.