Preparation Of BiFeO₃ Nanoparticles And Nanowires,and Effect Of Doping On The Physic Properties

BiFeO₃?BFO?showing a rhombohedrally distorted perovskite crystal structure with space group R3 c has long been known to be an antiferromagnetic,ferroelectric multiferroic with potential applications due to its high antiferromagnetic Neel temperature TN⁶43 K and ferroelectric Curie temperature TC¹103 K because of the inherent coupling between their magnetic order and ferroelectricity and their potential technological applications in many fields such as data storage,sensors,and spintronic devices.Recently,studies about BiFeO₃ have been concentrated on nanomaterials such as nanoparticle,nanowire,nanotube and nanorod.In our work,we synthesized low content Tb,Ba and K doped BiFe O3 nanoparticle using sol-gel method,and BFO nanowires calcined at 400 �C,500 �C and 600 �C by sol-gel electrospinning method.And detailed studies of multiferroic properties for all the samples were carried out.We prepared Bi1-x TbxFeO3?x=0,0.01,0.03,0.05?nanoparticles by sol-gel process.Single phase perovskite rhombohedral structure of all the samples have been established and the particle size decreases with increasing Tb content.Contrary to weak ferromagnetism,our samples present ferromagntism.Interestingly,the magnetization value of 1% Tb doped sample at 50 kOe is nearly as large as that of10% Tb-doped nanoparticles previously reported by Lotey et al.and is larger than that of 10% Gd-doped and 15% Pr-doped BiFeO₃ nanoparticle systems.The high content of Fe3+ in 1%Tb doping sample by XPS analysis is an significant factor for enhancing magnetization.Reduced leakage current density compared to the undoped BiFe O3 are observed due to decreasing oxygen vacancy.Additionally,The decrease in band gap may result from the reduced particle size,which have more unsaturated bonds on the surface of the nanoparticles.These unsaturated bonds could create deep and shallow levels with the band gap.Then,we selected Ba2+ and K1+ ions as dopant to substitute Bi3+ ions of BFO and prepared Bi0.9-xBa0.1KxFeO3?x=0,0.01,0.02?nanoparticles via a facile sol-gel method.The content capability of K dopant in our system can be attributed to the larger amount of barium at A-site,which helps to steady the perovskite structure of BFO phase and at the same time suppress the volatilization of Bi.All the samples present weak ferromagnetism.And the enhanced magnetization is mainly due to the decreased bond angle of Fe-O-Fe.The band gap values showed no obvious change with the increase of K content which was due to the interplay of oxygen vacancies and bondangle of Fe-O-Fe.Last,on basis of preparing BiFeO₃ nanoparticles,we synthesized BFO nanofibers calcined at 400 �C,500 �C and 600 �C by sol-gel based electrospinning method.the nanofibers 500 �C and 600 �C are comprised of continuous grains which are closely dense,packed and self-assembled.It is worth noting that samples calcined at 400 �C and 500 �C nearly reach saturation at about 8 kOe,while the sample calcined at600 �C show weak ferromagnetism.M-H curves at 300 K and 5 K and M-T curves under 500 Oe external field by both zero field cooled?ZFC?and field cooled?FC?conditions from 5 K to 350 K for the sample calcined at 600 �C were measured.And superparamagnetic behaviour was also found.