多铁性铁酸铋的合成与改性

III
Abstract
Preparation and modification of multiferroic bismuth ferrite
(3) In this dissertation, the perovskite structure of CuCa 3Ti4O12 was introduced into the crystal structure of BiFeO3. X-ray diffraction (XRD) patterns showed the reduce of impurities with the addition of CuCa3Ti4O12, and eliminated when 20 mol% added. The transformation of pseudotetragonal structure was also observed. Impedance measurements suggested a growth of boundary resistance, and CuCa3Ti4O12 addition could block the conduction path and stabilize the motion of defects. A frequency dependent relaxation process was observed on the analysis of dielectric. The dielectric constant and the loss tangent of BiFeO3 as a function of frequency were found to be increased on increasing CuCa3Ti4O12 contents. The addition of CuCa3Ti4O12 could affect the spin structure. It was explained by the formation of oxygen vacancy and Fe4+ by ionic doping and structure transformation. Keywords: BiFeO3, ultrasonic irradiation assisted self-combustion method, doping, ferroelectricity, ferromagnetism, photocatalysis
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中文摘要
多铁性铁酸铋的合成与改性
铁磁性分析可知，CuCa3Ti4O12 的加入可以影响铁酸铋自身的自旋结构，这主要是由 于离子掺杂导致氧空位与 Fe4+形成， 以及晶格结构发生改变导致磁旋结构发生变化而 引起磁性能变化。 关键词：铁酸铋、超声自蔓延法、掺杂、铁磁性、铁电性、光催化
作
者：王奔
பைடு நூலகம்
指导教师：周竹发 教授
ferroelectricity, ferromagnetism and ferroelasticity. As a typical single-phase multiferroic, the perovskite structure of bismuth ferrite (BiFeO 3) exhibits ferroelectric and antiferromagnetic properties above room-temperature. Multiferroics show potential applications in the field of magnetic storage medium and new devices based on the mutual controls of magnetic and electric fields. Moreover, the research of multiferroics is also very important for the couping of magnetic and electric parameters. In this dissertation, BiFeO3 was discussed and analyzed in detail, and synthesis and properties were improved as well. The main contents and conclusions in this dissertation are listed in the following: (1) In this dissertation, BiFeO3 nanoparticles were prepared by the combination of ultrasonic radiation and self-combustion. X-ray diffraction (XRD) patterns showed that BiFeO3 nanoparticles were prepared with a small amount of impurities. The reducing size effect of ultrasonic radiation was studied by Transmission electron microscopy (TEM) and Particle size analyzer. It was observed that the magnetization was antiferromagnetism, and the intrinsic spin structure was interrupted by reducing size, hence, the latent magnetization was released. The UV–vis absorption spectra showed the narrow energy bandgap of BiFeO3 nanoparticles. The enhanced degradation of MO was confirmed by the effect of reducing size and porous in the surface, which contribute to the increasing activity of absorption. (2) In this dissertation, Sr2+and Nd3+ were introduced into the crystal structure of BiFeO3. X-ray diffraction (XRD) patterns showed the dopant help the formation of impurities and reducing size. Regarding smaller particles, even if small amount substitution content change can result in the phase transition from the rhombohedral distorted perovskite to the pseudotetragonal. The substitution of Sr 2+and Nd3+ was induced for the improvement of magnetism, which could be attributed to two aspects: on the one hand, dopant would result in the slope of spin; On the other hand, size effect could enhance the magnetism.
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Preparation and modification of multiferroic bismuth ferrite
Abstract
Preparation and modification of multiferroic bismuth ferrite
Abstract
Multiferroics are multifunctional materials which exhibit coexistence of
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多铁性铁酸铋的合成与改性
中文摘要
中文摘要
钙钛矿结构的铁酸铋(BiFeO3)作为一种典型的单相多铁性材料，其在室温下可以 同时呈现出铁电性与磁性。 这种多铁性材料在磁存储介质方面有着极其重要的应用前 景， 能够成为集铁电材料和磁性材料于一身的新型记忆材料，并且其电性能与磁性能 参数的耦合在基础物理方面也具有极其重要的意义。 本文针对铁酸铋纳米粉体制备、Sr2+与 Nd3+离子掺杂、CuCa3Ti4O12 掺杂进行了系 统地研究与分析，并对制备的铁酸铋材料的性能进行表征，研究的主要结论如下： (1) 结合超声化学法与自蔓延法，制备出纳米级铁酸铋粉体。X 射线衍射(XRD) 数据表明， 制备出的粉体是含有少量杂相的纳米级铁酸铋；利用透射电镜与粒径分析 仪对制备出的粉体进行分析， 发现超声可以有效地减少纳米颗粒的半径；铁磁性分析 表明，制备出的铁酸铋呈现反铁磁性，由于颗粒半径的减少，打乱了原有的自旋结构 分布，使得磁性能释放出来；紫外光度分析仪分析表明，制备出的铁酸铋具有较小的 能带和优良的光催化使用前景；由于超声自蔓延法可以减小粒径大小，增加颗粒表面 孔洞，在光降解实验中，能够参与到反应的活性空位增多，有利于颗粒对甲基橙的吸 附，进而提高了光催化性能。 (2) 将 Sr2+与 Nd3+离子掺入到纳米铁酸铋晶格中，通过 XRD 分析，发现离子的 掺杂可以有效抑制杂相的生成， 并且随着掺杂量的增加，晶格结构由菱方相转变成伪 正方相，同时，离子掺入后能够减小晶粒的尺寸；相对于在宏观尺寸下的铁酸铋，掺 杂量在较少的情况下可以引起相转变的提前发生；由于掺杂的作用，Sr2+与 Nd3+离子 都可以提高铁酸铋整体的磁性能，其原因主要是掺杂元素可以使自旋结构发生倾斜； 另一方面磁性能也随着纳米粒径的减小而得到提升。 (3) 引入具有钙钛矿结构的 CuCa3Ti4O12 掺入到铁酸铋中，通过 XRD 分析，随着 掺杂量的增加，杂相减少，当掺杂量达到 20mol%，杂相基本消失，晶格结构转变成 伪正方相结构；阻抗分析表明，CuCa3Ti4O12 的加入可以提高铁酸铋的晶界电阻，增 加其活化能，降低了缺陷含量，抑制载流子的运动；介电分析表明，CuCa3Ti4O12 的 加入可以提高铁酸铋的介电常数，其原因可能与空间电荷和内部阻挡层电容有关；由