| BiFeO3is currently the most widely studied single-phase multiferroic materials.On the one hand, multiferroic material is a new multi-functional materials, it has abroad application prospect in spintronics, high speed memory and other areas. On theother hand, BiFeO3is the only single-phase multiferroic material both exhibitingferroelectric and multiferroic magnetic materials above room temperature. From theview of application, the current magnetic memory device read fast but the write speedis slow, magnetic memory device write fast but the read speed is slow. Multiferroicmaterials are likely to combine the advantages of both the magnetic memory deviceand magnetic memory device. Meanwhile, from the perspective of condensed matterphysics, multiferroic material has raised many fundamental issues and challenges inferroelectricity, magnetic and strongly correlated electron physics, making it a hottopic in the quantum control field. In recent years, the broad research of BiFeO3hasmade people have a deep understanding of the physical mechanism and successfullyexplore its possible applications. Some novel preparation methods and concepts havebeen developed and put forward, through combine with ferromagnetic material toachieve a strong magnetoelectric coupling. However, there seems to be moreproblems and challenges compared to the current research achievements. BiFeO3currently face three major problems. First, the leakage current in bulk material is solarge that the measured polarization is very small, which is too far from the theoreticalcalculation (100μC/cm2). Second, because of its incommensurate antiferromagneticspin arrangement with a period of about62nm, the modulation structure leads to themagnetic moments cancel out with each other. So BiFeO3with a macroscopic scaleshows only a very weak magnetization. Three, the magnetoelectric couplingcoefficient of BiFeO3is too small, which is not enough to the mutual regulationbetween the electric and magnetic fields. Silicates have been attracted great interestsowing to its abundant and environmental benign. In2005, Dr. Nyte’n from UppsalaUniversity in Sweden synthesized Li2FeSiO4materials for the first time,electrochemical test results show that this material has a certain electrochemicalactivity.My thesis work includes the following aspects:(1) We prepared BiFeO3and La-doped LaxBi1-xFeO3nanoparticles by sol-gel method. And explore the effects of different annealing process in the structure and magneticproperties.(2) We have prepared the La and Lu co-doped La0.1LuxBi0.9-xFeO3ceramics byconventional solid-state reaction method. When the Lu content exceeds5%, the XRDpattern can be indexed by two sets of different XRD patterns corresponding toLuFeO3and BiFeO3phases. There exists a significant shift of magnetic hysteresisloops, this phenomenon can be attributed to the impact of exchange bias interactionbetween the two Cant-AFM phases.(3) We have prepared in situ carbon-coated lithium-ion battery cathode materiallithium iron silicate by sol-gel.600°C is the optimal annealing temperature, with highcrystallinity, no impurity phases, good uniformity of the particles, and the particlesize distribute at20~30nm, the weight percentage of carbon is about12%. With ashort annealing time it will exist a large number of site-exchange of Li and Fe, andwith the annealing time increase,the site-exchange of Li and Fe will be decreased.Electrochemical tests discovered that both electron conductive and lithium ionsdiffusion coefficient are increased with the existence of a large number ofsite-exchange of Li and Fe.600°C annaling with4h have good crystallinity and thereexist a large number of site-exchange of Li and Fe, thus showing excellentelectrochemical performance, at the rate of1C, the initial discharge capacity is173mAh/g, at the rate of100C, the discharge capacity is80mAh/g, and even in the highrate of300C, the discharge capacity is45mAh/g. |
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