Structure And Properties Of BiFeO₃ With La, Pb Substitution

In recent years,multiferroic materials with coexistence of at least two ferroic orders (ferroelectric,ferromagnetic,or ferroelastic) have drawn increasing interest due to their potential for applications as multifunctional devices.Perovskite-type BiFeO₃ is one of the well known single-phase multiferroics with simultaneous ferroelectric and antiferromagnetic nature at room temperature.However BiFeO₃ has also disadvantages of low magnetization and small magnetoelectronic coupling effect,which is the obstacle to realize the practical applications of BiFeO₃ ceramics.In order to solve these problems,there are several reports on the fabrication of a solid solution of BiFeO₃ with other ABO₃ perovskite materials or some doped BiFeO₃ compounds.In this paper,Bi_1-xLa_xFeO₃,Bi_1-xPb_xFeO₃ and Bi_0.9-xPb_xLa_0.1FeO₃ were prepared by the conventional solid state reaction.Phase purity and microstructure of the ceramics were characterized by X-ray diffraction meter and scanning electronic microscope,respectively. The magnetic of the ceramics were also investigated.For the Bi_1-xLa_xFeO₃ and Bi_1-xPb_xFeO₃ samples,at the same doping content and sintering time,with the increasing of sintering temperature,the phase purity were both improved.At the same doping content and sintering temperature,with the increasing of sintering time,the phase purity of the both samples didn't change evidently.When the sintering time was 1 h,the both samples were already single phase.At the same sintering temperature and sintering time, for the Bi_1-xLa_xFeO₃ samples,with the increasing of doping content,the phase purity was improved.However for the Bi_1-xPb_xFeO₃ samples,the sample was purest when x=0.3.We researched Bi_1-xLa_xFeO₃ samples which calcined at 900℃for 2h,found that the magnetism of the samples were very weak.With the doping content increasing,the magnetism strengthened gradually.When the doping content increased to x=0.15,the magnetism enhanced obviously. However for the Bi_1-xPb_xFeO₃ samples which calcined at 810℃for lh,the M-H curve was a straight line basically and the magnetism was very weak when x=0.0,0.1,0.2.The M-H curve presented magnetic hysteresis and the magnetism increased when x=0.3,0.4. For the Bi_0.9-xPb_xLa_0.1FeO₃(x=0.0,0.1,0.2,0.3) samples,the structure research indicated that the doping content's difference had affected the sample phase purity directly.When x=0.2, the sample was purest.SEM observation showed that the particles exhibited approximate spherical shape and it was estimated that the diameter of the particles were between 300-400nm.We researched the magnetism of the Bi_0.9-xPb_xLa_0.1FeO₃ samples found that the M-H curve was a straight line basically and the magnetism was very weak when x=0.0,0.1. The M-H curve presented magnetic hysteresis when x=0.2.The magnetism increased when x=0.3.We researched Bi_0.85La_0.15FeO₃,Bi_0.7Pb_0.3FeO₃ and Bi_0.7Pb_0.2La_0.1FeO₃ which the phase purity were purest in the three series of samples,found that the magnetism of Bi_0.7Pb_0.3FeO₃ was far bigger than the magnetism of Bi_0.7Pb_0.2La_0.1FeO₃ and Bi_0.85La_0.15FeO₃.