| Nowadays, the researches of bismuth layer-structured perovskite single-phase multiferroic focus mainly on four-layered or higher-layered perovskite preparation and performance of multiferroic. Four-layered Bi5Ti3Fe15(BFTO) attracts wide attention and research for its ferroelectricity(FE) order but yet needs to be further researched for its weak magnetic order. This paper strives to find out how the multiferroic order is affected and changed through the improvement of the doping and preparation process by studying the micro-structure, electricity and magnetism of ceramic samples.The BFTO samples prepared by multi-step calcination method, which is evolved from the conventional ceramic method, is used to prepare multiferroic ceramic sample Bi4NdTi3Fe1-xMxO15(M:Cr/Co/Mn; x=0.1/0.3/0.5/0.7) with a Nd doping in A site and magnetic element M of various content in B site. Characterization of the micro-structure and multiferroic performance of the three different samples in B site have been made and analysis of the dielectric nature of part of the samples has been conducted.According to the analysis, the samples prepared by multi-step calcination method formed crystal structure of layer-structured perovskite, which possesses simultaneously FE properties and ferromagnetism in room temperature and has a significant enhancement compared with pure phase BFTO.1) in samples of Cr doping in B site, when x=0.1, the remnant polarization2Pr is21.579μC/cm2, which increased by82.87%compared with11.8μC/cm2reported by some researchers. Remnant magnetism2Mr presents a decrease-increase trend with increasing doping amount. When x=0.7,2Mr is334μemu/g, which is the highest.2) as for samples of Co doping in B site,2Pr increases along with the increase of external electric field. Samples of x=0.1,0.3and0.5have roughly the same2Pr in the same electric field. Samples of x=0.7presents a fairly high2Pr. Within our limited measuring range,2Pr is23.84μC/cm2, which is twice of the result of pure phase BFTO. In terms of ferromagnetism, the2Mr shows a trend of increase-decrease wit an increase of Co doping amount.2Mr=76.7memu/g, which is the highest, appears in samples of x=o.3.3) samples of Mn4+substitute Fe3+in B site, x=0.1and0.5share roughly the same2Pr in the same electric field, while x=o.7is quite different in that 2Pr is greatly improved. In the strongest electric field allowed,2Pr is11.209μC/cm2. As for ferromagnetism,2Mr is roughly the same among samples of x=0.1,0.5and0.7, while2Mr of x=0.3is12to20times higher than other Mn doping samples, which2Mr is59.007memu/g. When compared with2Pr=11.8μC/cm2and2Mr=2.72μemu/g of pure phase BFTO ceramics reported by related researchers, the samples exhibit great enhancement of ferromagnetism.2Mr of Co doping in B site increased by6orders of magnitude and FE order remains stable when ferromagnetism is greatly improved. The2Pr of samples of Co doping with x=0.7is twice of the result of pure phase BFTO. Nd doping on A site of BFTO by multi-step calcination method shows that magnetic elements doped in B site can improve the multiferroic. What’s more, different doping elements affect little on BFTO performance. It is assumed that the radius of doping ions and the lattice deformation brought by different doping amount paly a vital role in affecting multiferroic of pure phase BFTO.Besides, through the study of magnetic capacitor effect of part of the samples, whose dielectric constant is influenced by external magnetic field. It is found that relative dielectric constant decreased under the influence of external magnetic field, which shows that the samples exhibit certain magnetic capacitor effect. According to the viewpoint of other researchers, the samples possess certain degree of magnetoelectric coupling. |
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