The Preparation And Investigation Of Rare Earth Element Doped Layered Perovskite Materials

Along with the improvement of science and technology, single functional material couldn’t meet the diversity of practical application any more, thus seeking multi-functionalized material is the tendency of future technology. The realization of multi-functionalization depends on the coupling of multiple internal parameters and therefore response of multiple external fields. Layered oxides are the excellent candidates for the multi-parametric single phase materials due to their volatile crystal structure. However, most of these layered oxides belong to ferroelectric and dielectric system and there is nearly no coexist of magnetism and electricity above room temperature. In 2009, Mao, Chen, and Lu et al successfully manufactured a new single-phase magnetoelectric material Bi5Fe0.5Co0.5Ti3O15 through the atomic layer insertion method, which exhibited large ferroelectric and ferromagnetic response at room temperature. These researches show the concept of "recombined multi-parametric oxides quantum functional material". The previous studies of these materials were mainly about the electromagnetic and dielectric properties of ceramic and thin film, which may find possible applications in information storage, sensors or hard disk field and so on.Centering around this material system, the present thesis is mainly about the preparation and characterization of novel Co-doped layered oxide nano-materials containing rare earth elements and magnetic elements, tended to widen the application of such materials. By doping the layered oxide nano-material, we achieved both photo-catalysis under visible light and rapid magnetic recovery. We also used positron annihilation tactics to explore the relation between preparation temperatures and formation of defects. The thesis is organized as follows:Chapter 1:We introduce the development history of multiferroic materials and what our group explores in this field. As the possible application field including photocataysis, the principle of photocatalysis is also introduced, as well as the ferroelectricity and ferromagnetism behaviors, respectively. The research direction of the works in this thesis is also summarized:the preparation and performance research of nanostructured Bi5FeTi3O15 doped with rare earth metal elements, and also the control of morphology and properties, in order to fit different application purposes.Chapter 2:Different preparation methods for Bi5Fe0.95Co0.05Ti3O15 are introduced at first, including hydrothermal method, coprecipitation method, and citrate combustion method. Nanoparticles with different characteristic morphology, ferromagnetic and photocatalytic properties can be by obtained by varying the preparation methods, which can be used for different purposes.Chapter 3:Nanomaterials with improved photocatalysis and magnetism may enrich their applications in actual situations where both high light activity and good room-temperature (RT) magnetic recyclability are required. In this work, europium and cobalt co-doped Bi5FeTi3O15 nanoflowers were synthesized by a hydrothermal method, with goals to improve both photocatalysis activity and magnetism. The resulted Bi5-xEuxFe0.95Co0.05Ti3O15 nanoflowers exhibit good room temperature ferromagnetism, as well as acceptable UV-and visible-light-driven degradation capabilities, which can be improved by optimizing the Eu content. The improved magnetism supported a full retreat of such nanoflowers in water solution by applying a magnetic field at the RT environment.Chapter 4:The effect of sintering temperature on the multiferroic property was investigated in the work of this chapter, especially that the positron annihilation tactics have been taken to explore the defects evolution. The ferromagnetism was enhanced gradually with the increase of the annealing temperature (700-900 ℃) due to the grain grown and pinning effect weaken, while the ferroelectric polarization decreased sharply when the annealing temperature was higher than 800 ℃, and the reason may be the concentration of the defects which induced the electric polarization decreased to the minimum at about 800 ℃. This work suggested the importance of sintering temperature on the multiferroic property of ceramic and reveals the relationship between defects and property.Chapter 5:The main results of the works are summarized, and the future works for this research are suggested..