【作者】 董晓伟；

【导师】 金绍维；

【作者基本信息】 安徽大学 ， 材料物理与化学， 2011， 硕士

【摘要】 多铁性材料是一类同时具有两种或两种以上单一铁性(如铁磁-反铁磁性,铁电-反铁电性,及铁弹性)的材料,而且不同铁性之间的耦合协同作用可产生一些新奇的效应,例如,磁化强度和自发极化之间的磁电耦合效应,这些多功能特性为多铁性材料在电子器件等领域开启新的应用前景。在众多的多铁性材料中,BiMnO3因同时具有铁磁性和铁电性而备受人们关注。然而,因Bi基化合物的不稳定性和易挥发性,使得很难实现单一钙钛矿相的BiMnO3,另一方面,BiMnO3具有较低的铁磁转变温度Tc和室温下的高漏导性,这些都极大地限制了BiMnO3可能的应用。本文采用溶胶-凝胶法制备了多铁性Bi1-xLaxMnO3和Bi0.8La0.2Mn1-xFexO3陶瓷样品材料,研究了烧结温度对Bi1-xLaxMnO3样品钙钛矿相的影响,从而得到了制备单一钙钛矿相Bi1-xLaxMnO3的最佳烧结温度为一窄小的温区(925-950℃),并在此基础上研究了La掺杂对Bi1-xLaxMnO3的结构和磁性能影响。最后在确定最佳烧结温度和La掺杂含量之后,进一步研究了在Mn位掺杂Fe对Bi0.8La0.2Mn1-xFexO3样品的结构与电磁性能的影响。全文分为四章,各章的主要内容可概括如下：第一章本章简单回顾了多铁性材料的研究及其进展,介绍了单相多铁材料匮乏的原因和几种实现铁电铁磁共存的机制。重点介绍了BiMnO3的结构和电磁性能,在此基础上,介绍了目前BiMnO3研究中面临的一些问题,并根据相关文献提出了一些可能提高BiMnO3电磁性能的方法与方案。第二章本章主要介绍了本论文中Bi1-xLaxMnO3和Bi0.8La0.2Mn1-xFexO3样品的制备和测试表征等方法,并对每次测试的实验细节和仪器做了简要的说明。第三章本章研究了烧结温度和La掺杂依赖的Bi1-xLaxMnO3(BLMO,0.1≤x≤0.4)样品的结构和磁性能,我们的结果显示存在一个窄小的温度区间(925-950℃),在此温度区间烧结的BLMO具有稳定的钙钛矿相。随着La掺杂减少,样品中BLMO钙钛矿相减弱,铁磁转变温度(Tc)由53K降至41K,而饱和磁化强度经历了先降低再升高的变化。这可归因于La含量较少的样品中Bi空位浓度的增加诱导了Mn-O-Mn键角的减小和局域Mn4+离子的增多,使得Mn3+和Mn4+离子的铁磁超交换增强和Mn?+离子的dz2轨道有序受到局域破坏。第四章在最佳烧结温度和La掺杂的条件下,本章我们研究了在B位掺杂Fe对Bi0.8La0.2Mn1-xFexO3(BLMFO,0≤x≤0.9)样品的结构和电磁性能的影响。XRD测试显示x=0,0.1的样品的结构具有正交对称性,而x=0.3-0.9的样品的结构则具有四方对称性,研究发现样品的磁性能与其单胞结构有强烈的依赖关系。M-T曲线和M-H曲线测量显示出样品的磁相为：x=0,0.1的样品为FM态,随Fe含量x值的增加,样品的发生FM-AFM转变,x=0.3-0.9的样品表现出FM-AFM共存的磁特征。另外,P-E曲线测量表明样品的铁电性随Mn含量的增加逐渐减弱,这归因于过量的Mn离子会导致样品中Fe2+离子含量的增加,从而增加样品的漏导。更多还原

【Abstract】 One particular current interest is multiferroic materials in which two or three ferroic properties, namely, ferroelectricity(FE), ferromagnetism(FM), and ferroelasticity coexist in the same phase. Particularly, the combination of ferromagnetism and ferroelectricity with coupling between the spontaneous polarization and the magnetization through the magnetoelectric(ME) effect, because they can support novel functionalities in electronic devices. Multiferroic BiMnO3 has been widely renewed interest because BiMnO3 exhibits ferroelectricity and ferromagnetism ordering simultaneously. However, because of the high volatility of Bi for numerous Bi-based compounds, it is difficulty in preparing single perovskite BiMnO3. On the other hand, BiMnO3 also can’t support the applications because it’s low Curie temperature(Tc) for the ferromagnetic property and high leakage current at roomtemperature(RT).In this thesis, Multiferroic Bi1-xLaxMnO3 and Bi0.8La0.2Mn1-xFexO3 ceramics samples were synthesized by the sol-gel method. The sintering temperature influence on the perovskite phase of Bi1-xLaxMnO3 samples was carefully studied, it is shown that there was a narrow range of sintering temperature(900～950℃) for the stable perovskite BLMO sample. On this basis, it was carefully investigated that the La doping effect on the structural and magnetic properties of the Bi1-xLaxMnO3 samples sintered at 950℃. And then, the Fe doping effect on the structural and electromagnetic properties of the Bi0.8La0.2Mn1-xFexO3 samples sintered at 950℃was also carefully studied.The whole thesis consists of four chapters, the main contents in each chapter are presented as follows:Chapter 1:The general review of the history and present research situation of the multiferroic materials. We make a brief introduction to the reasons for lack of single-multiferrioc materials and several mechanisms for the coexistence of the ferroelectricity and ferromagnetism. And then, we particularly introduced the structure and electromagnetic properties of BiMnO3. On this basis, we introduced several problems in research of BiMnO3, and then we brought out several methods to improve the electromagnetic properties of BiMnO3 by the relevant literature.Chapter 2:The Bi1-xLaxMnO3 and Bi0.8La0.2Mn1-xFexO3 ceramics preparation methods and the samples measurement methods are introduced, especially the details and instruments of each experimental are introduced.Chapter 3:The sintering temperature influence on the perovskite phase of Bi1-xLaxMnO3 samples was carefully studied by using X-ray diffraction (XRD), scanning electronic microscope (SEM), fourier transformation infrared spectroscopy(FT-IR), and the thermo gravimetric analysis-differential thermal analyses (TG-DTA). It was also carefully investigated that the La doping effect on the structural and magnetic properties of the BLMO samples sintered at 950℃. Our results indicated that the perovskite phase of samples was weakened as La doping reducing, the Curie temperature Tc decrease from 53K to 41K, corresponding to the saturation magnetization experienced a lowering and then an enhancing. It was ascribed to the increase of Bi vacancies in La doping reducing samples, which induced a decrease of Mn-O-Mn bond angle and an increase of Mn4+ ions. This resulted in an enhancing of the ferromagnetic superexchange between Mn3+ and Mn4+ ions and a disrupting of the dz2 orbital ordering around the Mn3+ matrix.Chapter 4:The structural, magnetization, and electrical properties of Bio.8Lao.2Mn1-xFexO3 samples were carefully investigated. It was found samples with x=0,0.1 shown a distorted orthorhombic crystal structure, and a distorted tetragonal crystal structure for x≥0.3, and we also found a clear correlation between the magnetization and the crystal structure. A magnetic transition from a ferromagnetic (FM) state (x=0,0.1) to a antiferromagneic (AFM) state (x≥0.3) with increasing Fe content, and the samples had a competition between FM and AFM at room temperature for x≥0.3 were observed by M-T and M-H curves. Compared the polarization hysteresis loops of the sample for x=0.9 and x=0.7, it is seen with decreasing x, the samples have a higher leakage current, which leading to the weakened ferroelectric(FE). It was ascribed to that excessive Mn-doped in Bi0.8La0.2MnxFe1-xO3 system can increase the ratio of Fe2+/Fe3+, which weaken the ferroelectric.更多还原