The Lattice Distortion And Magnetic Enhancement By Ion Doped BiFeO₃

Bi1-xLaxFeO3,Bi1-xEuxFeO3,Bit-xHOxFeO3 and Bi1-xLaxFe0.99Nb0.01O3 samples were prepared by sol-gel method.The main conclusions in this work are as follows:1.Bi1-xLaxFeO3(0 ?x ? 0.25).All samples maintain R3c phase.La doping in bismuth ferrite gives rise to i)stretching distortion and displacement distortion,ii)decreasing angle of anti-rotated double FeO6 octahedron and iii)no distortion in the single FeO6 octahedral.La doping decreases Fe-O-Fe angles.Although the oxygen vacancies increase with increasing La doping content,the ratio of Fe3+ to Fe2+ remains stable with La doping.The stable content of Fe3+ in samples can be attibuted to no charge compensation because of the same valence state of Bi3+ and La3+.La doping can enhance magnetic properties of BiFeO3.It can be ascribed to the distortion of FeO6 octahedral that Fe-O-Fe bond angle decreases essentially.2.Bi1-xEuxFeO3(0 ?x ? 0.25).Eu doping causes phase transition in Bi1-xEuxFeO3 samples.It is R3c rhombohedral structure with Eu content x<0.15 while it is Pbnm structure with Eu content x>0.20.Eu doping in BiFeO3 results in i)stretching distortion and displacement distortion,ii)decreasing angle of anti-rotated double FeO6 octahedron and iii)no distortion in the single FeO6 octahedral.Oxygen vacancies decrease in Bi1-xEuxFeO3 while the ratio of Fe3+ to Fe2+ remains the same by Eu doping.The decreasing Fe-O-Fe bond angle that improves DM interaction by Eu doping enhances magnetic properties.3.Bi1-xHOxFeO3(0<x<0.25).Ho doping causes phase transition in Bii-xHoxFeO3.It maintains R3c rhombohedral structure with Ho content x<0.10.It is Pbnm phase with Ho content x ? 0.15.Ho doping generates stretching distortion and displacement distortion.The angle of the double FeO6 octahedral decreases with Ho doping in Bi1-xHoxFeO3.The O-Fe-O angle in the single FeO6 octahedral remains no change.Oxygen vacancies decrease by Ho doped in Bi1-xHoxFeO3.It can be attibuted to depressed volatilization of Bi by Ho doped in Bi1-xHoxFeO3.The ratio of Fe3+ to Fe2+ remains stable in all samples.The improvement of magnetic properties caused by enhanced DM interaction attributed to decreasing Fe-O-Fe bond angle.4.La,Eu or Ho doping gives rise to lattice distortion,respectively.Ho doping results in the biggest strctching distortion and displacement because of the smallest ionic radii(rLa>rEu>rHo)compared to La3+ or Eu3+.La Eu or Ho doping can decrease anti-rotation angle of the double FeO6 octahedral while can't cause distortion of the single FeO6 octahedral.The Fe-O-Fe angles decrease by rare earth ion The smaller the ion radius of the dopant,the faster the Fe-O-Fe bond angle decreases.All the La Eu or Ho doping enhance magnetic properties.The smaller the radius of the dopant ions,the more obvious the magnetic enhancement effect is caused.The improvement of magnetic properties can be attributed to the enhanced DM interaction caused by rare earth doping.5.Bi1-xLaxfe0.99Nb0.01O3(x<0.25)samples are prepared by sol-gel method.The crystalline structure,grain size and the magnetic properties of BI1-xLaxFe0.99Nb0.01O3 nanopowders are investigated by synthesized measurements.All samples are consistent of an R3c rhombohedral structure with decreasing Fe-O-Fe bond angles as the La concentration increases.La and Nb co-doping do not change the ratio of Fe3+ to Fe2+ in doped BiFeO3 system.The remnant magnetization is found that it depends strongly on La doping amount x.It is shown that the La-doping dominates the anti-rotation of the FeO6 octahedral,while the low doping of Nb results in the refinement of the grains.Both mechanisms would give rise to the magnetization enhancement in bismuth ferrite.