Multiferroic Properties Studies Of Doped BiFeO₃-BaTiO₃ Solid Solution

Multiferroic materials were a hot research topic because the great potential applications in sensors,information storage and new functional converters.Being the only single phase multiferroic material with ferroelectric and antiferromagnetic at room temperature,BiFeO₃ has a Neal temperature of T_N³70℃and the ferroelectric phase transition temperature（Tc⁸50℃）.It stands out in a large number of multiferroic materials,which shows great potential for the application of the real device.However,some inherent problems limit the application and development,such as the pure phase is difficult synthesized and the Bi³⁺ion easily volatilized at high temperature;the leakage current is too large,which inhibits the ferroelectric properties,and the inherent special magnetic structure leads to the weak macroscopic magnetism,and the weak magnetoelectric coupling effect.In this paper,based on the Samita Pattanayak’s research that the Sm elements doped BiFeO₃ can effectively improve the ferromagnetic properties of the system,we have studied the Sm doped BiFeO₃-BaTiO₃ solid solution.First,the solid solution formed by BiFeO₃ and BaTiO₃ can effectively inhibit the impurity phase and compensate the oxygen vacancy caused by the Bi³⁺ion volatilization.Secondly,there is a morphotropic phase boundary between BiFeO₃ and BaTiO₃ in a certain proportion of solid solution,which can obtain better ferroelectric properties and piezoelectric properties.Therefore,the Sm doped BiFeO₃-BaTiO₃ system is very likely to obtain obvious magnetoelectric coupling effect,and it will play an important role in promoting the practical application of BiFeO₃.The main research work of this paper is as follows:（1）0.71Bi_1-xSm_xFeO₃-0.29BaTiO₃（x=0-0.06）（ie:0.71BFO-0.29BT）multiferroic ceramic materials were prepared by the traditional solid phase method.The micro-morphology,phase structure,multiferroic properties,leakage current and magnetoelectric coupling properties of the 0.71BFO-0.29BT system with the variation of the doping amount of Sm ions were systematically studied.Combined with synchrotron radiation X ray absorption spectrum,the influence of Sm doping on the electronic structure of the system was studied,and the internal relationship between the electronic structure and the change of the multiferroic properties was analyzed.After the A site Bi³⁺ions are partially replaced by Sm³⁺ions,the structure of the system can be changed.When x=0.03,0.04 the system keeps the state of two phase coexistence,which called the morphotropic phase boundary（MPB）structure.The maximum residual polarization P_r=3.83μC/cm2（x=0.04）and the maximum saturation magnetization 3.43emu/g（x=0.03）were obtained near the MPB,and the distinct magnetic dielectric effect was observed in the samples of x=0.03,and the magnetocapacitance was as high as¹.3%.About the electrical insulation,the electrical insulation of BaTiO₃-BiFeO₃ solid solution is greatly improved compared with BiFeO₃,but the doping of Sm element reduces the electrical insulation of the solid solution,and the leakage current range of the system is 1.77×10^-7-1.16×10^-5（A/cm²）.It is found that with the appearance of the morphotropic phase boundary,the degree of hybridization between the Bi 6sp and the O 2p orbit reduced,thus the ferroelectric properties of the system are improved,and there are some specific relations between them.However,with the change of system structure,there is no obvious change in the coupling between Fe 2p orbit and 3d orbit.（2）the x Bi(Mg_2/3Nb_1/3)O₃ modified（0.71-x）BiFeO₃-0.29BaTiO₃ samples（x=0.0,0.01;0.02 0.03;0.06）were successfully prepared by the traditional solid state reaction method.The effect of the composite perovskite structure oxide on the ferromagnetic properties of BiFeO₃-BaTiO₃ system was studied.The phase structure,surface morphology,ferroelectric properties and electrical insulation of the doped system were analyzed.It is found that with the increase of Bi(Mg_2/3Nb_1/3)O₃ doping amount,the system maintains a single phase structure,and there is no coexistence of two phases.After doping,the average grain size of the system gradually increased,the uniformity became worse,and the porosity increased.The P-E curves show that Bi(Mg_2/3Nb_1/3)O₃ doping can effectively improve the ferroelectric properties of the system,but reduce the electrical insulation of the sample,and the leakage current range of the system is4.5×10^-7-1.68×10^-6（A/cm²）.In terms of magnetic properties,when x=0.03,we have obtained a maximal saturation magnetization M_S=1.39emu/g.This result is infrequent in many related studies.It is indicated that the doping of the complex type perovskite oxide Bi(Mg_2/3Nb_1/3)O₃to BiFeO₃-BaTiO₃ system can greatly improve the ferromagnetic property of the system.