Study On The Preparation And Magnetic/electric Prdopoperties Of Doped Bi_m+1Fe_m-3Ti₃O_3m+3 Multiferroic Material

As a kind of materials with both ferroelectricity and ferromagnetism,multiferroic materials have been widely studied because of their potential applications and extraordinary coupling effects.Bim+1Ti3Fem-3O3m+3 as a single-phase multiferroic material with layered perovskite structure has ferroelectricity and weak magnetism at room temperature,simultaneously.It has been considered as one of the most potential singlephase multiferroic materials at room temperature.This work successfully prepared pure Bim+1Ti3Fem-3O3m+3 powders and ceramics.The crystal structures were investigated and the magnetoelectric properties were analyzed via XRD Rietveld refinements.The pure orthorhombic powders possessed homogeneous composition and had flake grain.With increasing of m values,the rate of a/b increased first and then decreased slightly.The maximum rate of a/b was 0.99696 at m = 6 via the analysis of XRD refinement.By the temperature dependent dielectric curve,second-order phase transition happened at high temperature.By means of Nd doping and magnetic ions doping,the ferroelectric and ferromagnetism properties of this kind of material were optimized successfully.The influence of process parameters during fabrication was also studied.In this project,we found that the ratio of solvent and catalyst need to be strictly controlled to fabricate Bim+1Ti3Fem-3O3m+3 and its doped components using sol gel method.After obtained the uniform xerogel,segmental calcination process is needed to obtain the pure phase ceramics powders.For Nd doped ceramics,Nd substituted the B-site to replace Bi in perovskite structure(ABO3).The sinter ability of ceramics was improved obviously,and the relative density of ceramic was up to 96%.The breakdown-field increased from 80 k V to 180 k V,and the remnant polarization reached to 15.2 ?C/cm2 for 0.5 Nd doping.The enhancement in ferromagnetism of Nd doped ceramics is subtle and the doped component is still paramagnetic at room temperature.Magnetic-ion(Co/Ni/Mn)doping significantly changed the ferromagnetic properties of Bi6Fe2Ti3O18 ceramics.Especially in the x = 0.5 Co-doped component,ceramics showed ferromagnetism at both room temperature and liquid helium temperature.High susceptibility(Ms=4.21 emu/g)was obtained in Co-doped ceramics.It can be proved that the magnetism is intrinsic by Raman spectrum and Bohr magneton number calculations.The susceptibility was relatively small(Ms=3.48 emu/g)for Ni-doped materials.For Mndoped samples,the material exhibited superparamagnetism at low temperature while it was still paramagnetism at room temperature.In addition,the doping Co improved the ferroelectric properties of ceramics where the leakage current of materials decreased and the residual polarization value increased up to 9.6 ?C/cm2.