Synthesis Of BiFeO₃Ceramicsand Nanowires And Study On Effects Of Aliovalent Dopant On Their Physical Properties

More and more attention has been paid to multiferroic materials, owing to their physical mechanisms and potential applications for the design of multifunctional device. BiFeO3(BFO) is one of the few known multiferroic materials, with the high ferroelectric Curie temperature (Tc-1103K) and high antiferromagnetic Neel temperature (TN～643K). BFO has a rhombohedrally distorted perovskite structure, which belongs to the R3c space group. It is also an interesting candidate of application due to its coupling between ferroelectric and magnetic ordering at room temperature. Except for the advantages, BFO also has some inherent problems such as the difficulty of purification, weak magnetic characteristics and lower magnetoelectric coupling coefficient. Its antiferromagnetic characteristics are given by a spatially modulated spin structure that does not allow net magnetization and inhibits the observation of a notable linear magnetoelectric effect coupling between polarization (P) and magnetization (M). Therefore, the weak magnetization has limited the applications of BFO ceramic.La0.1Bi0.9AgxFe(1-x)03(LBFAX, x=0-0.05) ceramics were synthesized successfully by a modified rapid thermal process. It is found that the LBFAX with Ag dopant have dense microstructure with a reduced grain size. Simultaneously, Ag doping can increase dramatically the electrical conductivity of LBFAX ceramics by2-4orders of magnitude depending on the Ag concentration. The enhanced electrical conductivity of LBFAX ceramics was analyzed and attributed to the increasing concentration of oxygen vacancies induced by Ag doping.La0.1Bi0.9-xSrxFeO (3-x2)(LBFSX0≤x≤0.8) ceramics were synthesized by solid-state reaction method, and their magnetic properties and conductive characteristics were investigated and discussed. With the increase of the Sr2+concentration, the phase transits gradual from rhombohedral to pseudo cubic. Electrical and magnetic properties show strong dependence on Sr2+dopant level. The measurement demonstrates that LBFSX with30%Sr2+dopant exhibits the lowest values of the leakage current, dielectric constant (ε) and dielectric loss (tanδ). And the highest value of saturation magnetization of about4.5emu/g is observed in60%Sr-doped LBFSX.Nd0.1Bi0.9FeO3(NBFO),one-dimensional (ID) nanomaterials were synthesized using a sol-gel based electrospinning method. The samples were calcinedat different temperatures. As observed, it is clear that NBFO400and NBFO450exhibit the one-dimensional tubular structure with large inner diameter of～55nm and wall thickness of～20nm. The observation of an enhanced saturation magnetization and small hysteresis loss in NTs paves a new ways for improving magnetic properties of BFO, which can find applications in magnetic recording devices.