铁酸铋基粉体的化学法制备、表征及性能研究

发布时间：2018-05-11 15:07

本文选题：铁酸铋 + 掺杂　；参考：《华南理工大学》2014年硕士论文

【摘要】：多铁性材料在某一温度范围内同时具有铁电和铁磁性能，在新一代信息存储器、传感器和自旋电子器件等领域有着重要的应用前景。铁酸铋（BiFeO3）是单相多铁性代表材料之一，因其具有很高的铁电居里温度（Tc=830oC）和反铁磁尼尔温度（Tn=370oC）而备受关注。然而，在BiFeO3制备过程中通常会生成Bi2Fe4O9和Bi25FeO40等杂质，导致其漏电流增大。制备单相BiFeO3材料并提高其铁电铁磁性能已成为国际上大研究热点之一。本论文分别采用溶剂热法、溶胶凝胶法—水热法、水热法和软化学法等化学法制备了BiFeO3及Bi1-xNdxFeO3（BNFO）、Bi1-xLaxFeO3（BLFO）纳米粉体，并用扫描电镜（SEM）、扫描电镜能谱（EDS）、X射线衍射仪（XRD）、差热分析仪（DTA）磁性能测试仪等分析测试手段对纳米材料的尺寸、结构、形貌及其电性能、磁性能进行了表征。主要内容如下：（1）首次采用乙醇-水混合溶剂作为水热溶剂，在120℃低温下成功地水热合成了纯BiFeO3纳米粉体。在合成过程中，溶剂的成分和比例是对铁酸铋的生成具有重要的影响。只有当乙醇-水比例在4:3和2:5之间时，才能在低至120℃下合成单相BiFeO3粉体。该温度是目前合成铁酸铋的最低温度。用4:3乙醇-水混合溶剂合成的BiFeO3纳米粉体主要是由尺寸在50nm~150nm的颗粒组成的立方结构。ZFC和FC磁性能测试表明，BiFeO3纳米粉体在冻结温度5K下，具有玻璃态转化的现象。BiFeO3纳米粉体在室温下展现出铁磁有序，者可用尺寸效应来解释，同时在BiFeO3样品中也得到了电滞回线。室温下的铁磁有序和铁电有序，证明了纯BiFeO3晶体具有多铁性能。（2）采用新颖的溶胶-凝胶-水热法合成了多铁性Bi1-xNdxFeO3(BNFO, x=0-0.35)粉体。结果发现，在x≤0.25时能合成单相的Bi1-xNdxFeO3晶体，而合适浓度的KOH和NaOH分别有利于合成纯的Bi1-xNdxFeO3和Bi2Fe4O9晶体。扫描电镜结果表明BNFO晶体呈球形，其尺寸对KOH的浓度很敏感。BNFO晶体的铁电居里温度随着Nd掺杂的增加而向低温移动。磁性能测试结果表明，随着Nd掺杂量的增加，样品的磁性能得到增强。此外，我们还讨论了Bi1-xNdxFeO3晶体的形成机制。（3）用水热法合成了镧掺杂的铁酸铋晶体（Bi1-xLaxFeO3，x=0，0.15，0.3和0.4）。在合成过程中，前驱体的成分、氢氧化钾的浓度、水热合成的温度和时间，都对Bi1-xLaxFeO3的结晶和颗粒形貌发挥着重要的作用。当x＜0.3时，可以合成纯的Bi1-xLaxFeO3晶体，而且随着La的掺入量的增加，铁电转变温度从834.2℃降低至828.7℃。讨论了Bi1-xLaxFeO3晶体的生长机理。而且，实验结果表明，，La的掺入大大的提高了剩余极化。（4）使用酒石酸作为络合剂，采用软化学法合成了Bi1xNdxFeO3粉体。通过XRD、DTA、FT-IR和TEM等方法表征合成的粉体。结果表明，采用500℃就能合成结晶良好的单相Bi1xNdxFeO3粉体，其尺寸在30~50nm之间。磁性能测试表明，随着Nd的掺入，BNFO的磁性能得到提高。当Nd掺杂量达到0.2时，Bi1xNdxFeO3纳米粉体的磁性能达到最大，此时矫顽场达Hc=15368Oe，剩余磁化强度Ms=0.1944emu/g，M-H回线面积达到最大。
[Abstract]:Ferroelectric and ferromagnetic properties at a certain temperature range have an important application prospect in the new generation of information memory, sensors and spintronic devices. Bismuth ferrate (BiFeO3) is one of the single-phase multi iron representative materials, because of its high ferroelectric Curie temperature (Tc=830oC) and antiferromagnetic Neal temperature (Tn= 370oC) has attracted much attention. However, in the process of BiFeO3 preparation, impurities such as Bi2Fe4O9 and Bi25FeO40 are usually generated, which leads to the increase of leakage current. The preparation of single-phase BiFeO3 material and the improvement of ferroelectric ferromagnetism have become one of the hot research topics in the world.
In this paper, BiFeO3 and Bi1-xNdxFeO3 (BNFO), Bi1-xLaxFeO3 (BLFO) nanoscale powders were prepared by solsol-gel method, sol-gel method, hydrothermal method, hydrothermal method and soft chemical method. Scanning electron microscopy (SEM), scanning electron microscopy (EDS), X ray diffractometer (XRD), differential thermal analyzer (DTA) magnetic energy tester and other analytical instruments were used in this paper. The size, structure, morphology, electrical properties and magnetic properties of nanomaterials were characterized.
(1) the ethanol water mixed solvent was used as a hydrothermal solvent for the first time, and the pure BiFeO3 nano powder was synthesized successfully at 120 C at low temperature. In the process of synthesis, the composition and proportion of the solvent have an important influence on the formation of bismuth ferrate. Only when the proportion of ethanol water is between 4:3 and 2:5, the single phase BiFeO3 can be synthesized at low to 120. The temperature is the lowest temperature for the synthesis of bismuth ferrite at present. The BiFeO3 nano powders synthesized by 4:3 ethanol water mixed solvent are mainly cubic structure.ZFC and FC magnetic properties of the particles in 50nm~150nm particles. It is shown that the BiFeO3 nano powder has the phenomenon of glass state transformation at the freezing temperature 5K, and the.BiFeO3 nano powder is in the chamber. The ferromagnetic order is displayed at the temperature, which can be explained by the size effect. At the same time, the hysteresis loop is also obtained in the BiFeO3 sample. The ferromagnetic order and the ferroelectric order at room temperature prove that the pure BiFeO3 crystal has the properties of multi iron.
(2) a novel polyferric Bi1-xNdxFeO3 (BNFO, x=0-0.35) powder was synthesized by a novel sol-gel hydrothermal method. The results showed that the single phase Bi1-xNdxFeO3 crystal could be synthesized at the x < 0.25. The suitable concentration of KOH and NaOH was beneficial to the synthesis of pure Bi1-xNdxFeO3 and Bi2Fe4O9 crystals respectively. The results of scanning electron microscopy showed that the BNFO crystal was spherical and its size was opposite. The concentration of KOH is sensitive to the ferroelectric Curie temperature of the.BNFO crystal moving to the low temperature with the increase of Nd doping. The magnetic energy test results show that the magnetic properties of the samples are enhanced with the increase of the amount of Nd doping. In addition, we also discuss the formation mechanism of the Bi1-xNdxFeO3 crystal.
(3) lanthanum doped bismuth ferrite crystals (Bi1-xLaxFeO3, x=0,0.15,0.3 and 0.4) are synthesized by hydrothermal method. In the process of synthesis, the composition of the precursor, the concentration of potassium hydroxide, the temperature and time of hydrothermal synthesis, play an important role in the crystallization and particle morphology of Bi1-xLaxFeO3. When x < 0.3, the pure Bi1-xLaxFeO3 crystal can be synthesized. With the increase of the amount of La, the transition temperature of ferroelectric decreased from 834.2 to 828.7 C. The growth mechanism of Bi1-xLaxFeO3 crystal was discussed. Moreover, the experimental results showed that the addition of La greatly increased the residual polarization.
(4) using tartaric acid as the complexing agent, Bi1xNdxFeO3 powder was synthesized by soft chemical method. The powder was characterized by XRD, DTA, FT-IR and TEM. The results showed that a good crystalline single phase Bi1xNdxFeO3 powder could be synthesized by 500 C. The size of the powder was between 30~50nm. The magnetic properties test showed that the magnetic properties of BNFO were obtained with the incorporation of Nd. When the doping amount of Nd reaches 0.2, the magnetic properties of Bi1xNdxFeO3 nano powders reach the maximum, at this time the coercive field reaches Hc=15368Oe, the residual magnetization is Ms=0.1944emu/g, and the area of the M-H return line reaches the maximum.

【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM221

【共引文献】