Electrical And Magnetic Properties Of Aurivillius Phase BTXO Series Compounds

Magnetoelectric multiferroic materials can use an electric field to control the magnetic state,and vice versa.Such materials have important application prospects in future information technology and spintronic devices,and thus have become a research hotspot in the field of materials in the past decade one.Among them,the Aurivillius phase layered structure material having the general formula(Bi₂O₂)²⁺(A_m-1B_mO_3m+1)^2-(m:number of pseudoperovskite layers)has attracted our attentions.Such compounds have ferroelectricity at room temperature,and their ferroelectric transition temperature is 1021K.It is important that the B sites of these Aurivillius phase compounds can accommodate elements with different valence states,including various magnetic elements,such as Fe,Mn,Ni,etc.,and this will provide the possibility of the orderly generation of magnetism and make the materials multiferroic.However,most of the research on such materials is focused on thin films.Due to the surface or strain effect of the thin film,its properties may be different from that of the bulk.The properties of thin films are affected by the substrate,and the study of the intrinsic properties of the material is affected to a certain extent.High-quality crystalline materials make it easier to obtain the intrinsic properties of the materials.Therefore,we proposed to prepare Bi5Ti3XO15(X=Cu,Mn,Ni,V)ceramisc and crystals in this paper.They were prepared by different methods,and their crystal structures,ferroelectric properties and magnetic properties were systematically studied by X-ray diffraction,ferroelectric test system,magnetic measurement system and other characterization methods.(1)This subject proposes to prepare a series of Bi5Ti3XO15(X=Cu,Mn,Ni,V)ceramics with a layer structure of Aurivillius phase bismuth by a two-step sintering method.The two-step sintering method has the advantages of low sintering temperature,uniformity and compactness of the ceramics produced,and is conducive to improving electrical properties.Bi5Ti3XO15(X=Cu,V,Ni)ceramics have stable ferroelectricity under different applied electric fields(2-7k V).At 7k V,the residual polarization(2Pr)of the three samples is 5.68?C/cm²,4.66?C/cm²,1.54?C/cm².However,Bi₅Ti₃XO₁₅(X=Mn)does not have a ferroelectric circuit,and a dielectric fracture occurs when an external electric field of 10 k V is applied.Magnetic studies have found that Bi5Ti3XO15(X=Cu,Ni)has a coercive field of 0 at room temperature and is paramagnetic,but exhibits ferromagnetism at low temperatures(5K);while Bi5Ti3XO15(X=Mn)shows a weak anti-ferromagnetic,with a competion of ferromagnetic and ferrimagnetic ordering at low temperature(5K);Bi5Ti3XO15(X=V)ceramics have a negative correlation with the applied magnetic field,showing diamagnetic properties.(2)This subject proposes to prepare a series of Bi5Ti3XO15(X=Cu,Mn,Ni,V)crystals of Aurivillius phase bismuth layer structure by the micro-floating zone method.The micro-floating zone method is an effective method for exploring new crystals.It has many advantages such as many adjustable parameters,short growth period,and convenient real-time observation.It is a good method for obtaining high-quality bismuth-containing oxides with uniform composition.The Bi5Ti3XO15(X=Cu,V,Ni)crystal is a ferroelectric at room temperature.Under a applied electric field at 7 k V,its 2Pr is 16.26?C/cm²,13.64?C/cm²,and 4.74?C/cm²,respectively.The coercive force of the Bi₅Ti₃XO₁₅(X=Mn)crystal after polarization is zero,and the hysteresis loop is linearly correlated with the applied electric field,indicating that the dielectric hysteresis loop is measured.In the Bi5Ti3XO15(X=Cu)reciprocal susceptibility and temperature fitting curve,the horizontal axis intercept is 0,and there is hysteresis in the ferroelectric loop.The analysis may have a short-range magnetic sequence.The hysteresis loop of Bi5Ti3XO15(X=Ni)is linear at 5K and 300K,and its Curie-Weiss fitting curve passes through the origin,which is paramagnetic at room temperature and ferromagnetic at low temperature.Based on the Curie-Weiss law,it was found that the field cooling(FC)curve higher than the 45 K transition temperature can be fitted well,where the 45.6 K Weiss temperature is a positive value,indicating low temperature ferromagnetic order.The reverse hysteresis loop of Bi5Ti3XO15(X=V)indicates that it is diamagnetic.This study shows that due to the barriers from the(Bi2O2)²⁺layer and the pseudo-perovskite layer,it is difficult to form long-range magnetic order in such Aurivillius phase.