铁酸铋(BiFeO3，BFO)是至今唯一已知的室温单相多铁性化合物，由于其优异的电、磁、光性能，已成为研究的热点材料。目前针对BiFeO3的A 位、B位掺杂及A、B位共掺杂金属离子的改性研究较多，而针对O位的非金属离子掺杂的研究相对较少。 本论文分别使用室温固相反应前驱体法、高温固相法、水热法，详细的研究了F、Cl、Br、I、B、C、N、S等非金属离子掺杂对BiFeO3粉体磁性能和 光性能的影响。并使用Materials Studio 5.5计算软件的CASTEP模块对卤素掺杂BiFeO3的光磁性能进行理论计算及机理探讨。 具体的工作包括以下几个方面： (1) 在多铁材料的研究中，纯相BiFeO3样品的制备一直是研究的热点，本论文探索了一种室温固相反应前驱体法制备BiFeO3粉体的新工艺。通过热处理温 度、原料种类、NaNO3和聚乙二醇辅助等控制手段得到了BiFeO3微纳米粉末，使用室温固相反应前驱体法制备的BiFeO3粉体形貌以近球形颗粒为 主，不同的热处理温度及原料可以使BiFeO3粒径在18 nm到600 nm之间有效调控。受量子尺寸效应影响，BiFeO3光学吸收带隙和磁性能随着粒径减小而呈现出明显增大的趋势，NaNO3的添加使颗粒分散性得以改善， 聚乙二醇的添加使其磁性能显著增强。并且Cl、N非金属离子掺杂在增大磁性能的同时，能够减小吸收带隙，增强材料吸收太阳光的能力。 (2) BiFeO3材料在太阳能电池光电极、光解水制氢等方面有着广阔的应用前景。兼具可见光吸收特性和磁分离性质的BiFeO3，可以利用外磁场对材料在溶液 中进行定位，并且回收分离后可重复使用，从而大大节约成本。BiFeO3的光伏性能与极化具有紧密联系，使其光伏特性的调控有望通过电场、磁场两种不同方 式来实现。本论文用高温固相法合成了卤素(X：Fe=1-10%，X= F, Cl, Br, I)原子掺杂的BiFeO3。发现卤素掺杂明显提高了BiFeO3样品的磁性能，掺杂样品的最大矫顽场为87-207 Oe，最大剩余磁矩为8.25×10-4-4.85×10-3 emu/g。最大矫顽场按：I-BFO>F-BFO>Br-BFO>Cl-BFO>纯相BFO 变化，最大剩余磁矩按：Br-BFO>F-BFO>I-BFO>Cl-BFO>纯相BFO变 化。掺杂样品的吸收带隙与未掺杂样品相比更窄。掺杂后样品的最小光学吸收带隙按：纯相BFO>F-BFO>Br- BFO>I-BFO> Cl-BFO变化(分别为2.2 ev、2.1 ev、2.07 ev、2.04 ev、2.02 ev)。 (3) 目前新材料的设计和性能调控仍然常以“炒菜”式研究进行摸索和尝试。本论文使用Materials Studio 5.5计算软件的CASTEP模块，利用密度泛函理论(DFT)和虚晶近似(VCA)的方法对卤素元素掺杂O位后BiFeO3的生成焓、结构和光、磁性质 变化进行理论计算及机理探讨。分子模拟计算表明BiFeO3生成焓随F和Cl掺杂浓度的增加而减小，随Br和I掺杂浓度的增加而增加。BiFeO3晶格的 c轴膨胀随卤素原子掺杂浓度和原子序数的增大而增加。DFT法计算得到卤素离子掺杂BiFeO3的能带结构图，发现卤素掺杂后可以明显减小BiFeO3的 带隙，掺杂后BiFeO3的带隙按：I-BFO>Br-BFO>Cl-BFO>F-BFO>纯 相BFO变化与实验结果相近。CASTEP计算表明：卤素低掺杂时BiFeO3从反铁磁向铁磁性转变；而高掺杂时铁磁性又向反铁磁性转变，计算结果与实验 结果一致。 (4) 由于形状的各向异性及径向尺寸限定作用，非等轴形貌的颗粒在磁性能和光性能方面都具有优势。同时，非金属掺杂对形貌具有调控作用。研究非等轴形貌与非金属 掺杂协同作用下BiFeO3的磁、光性能的变化规律具有重要的科研价值。本论文在水热体系中研究了非金属离子(X：Fe=1-10%，X=F, Cl, Br, I, B, C, N, S)掺杂对BiFeO3物相结构、非等轴微观形貌的作用规律。XRD测试表明非金属掺杂后，BiFeO3晶格以膨胀为主，仅在B低掺杂时发现了晶格的收 缩。受非等轴形貌和非金属掺杂协同作用的影响，水热法比高温固相法更加明显地提高了BiFeO3样品的磁性能，掺杂样品的最大矫顽场为319-2650 Oe，最大剩余磁矩为7.6×10-3- 7.7.×10-2 emu/g。最大矫顽场按：B-BFO>Cl-BFO>C-BFO>N-BFO> F-BFO>I-BFO>S-BFO>Br-BFO>纯相BFO变化，最大剩余磁矩按Cl- BFO>F-BFO>B-BFO> C-BFO>N-BFO>S-BFO>I-BFO>Br-BFO>纯相BFO变 化。与固相法得到的粉体相比，水热反应得到的非等轴形貌粉体的光学带隙变窄。吸收带隙按：Br-BFO>I-BFO>C- BFO >Cl-BFO >N-BFO >B-BFO >纯相BFO>S-BFO>F-BFO变化(分别为2.2ev、2.17 ev、2.15 ev、2.11 e、2.1 ev、2.04 ev、2.03 ev、2.01 ev、1.98 ev)。

Bismuth Ferrite (BiFeO3, BFO) is the only known single-phase multiferroic material at room temperature. Because of its excellent electrical, magnetic and optical performance, it has been an extensively studied material. Most of the BiFeO3 modification studies focus on the metal ion doping in A site，B site, A-and B- site, while the study of the nonmetal ion doping in O site is relatively insufficient. In this dissertation, room temperature solid state precursor method, high-temperature solid-state method and hydrothermal method are adopted to synthesize nonmetal-doped (F, Cl, Br, I, B, C, N, S) BiFeO3 powder. The effects of nonmetal doping on the magnetic and optical properties of BiFeO3 powder are investigated in detail. The magnetic and optical properties of halogen-doped BiFeO3 have been calculated with CASTEP software package of Materials Studio 5.5. The major work can be described as follows: (1) The preparation of pure phase BiFeO3 is one of the hot issues in the research of multiferroic materials. A new technology for preparation of BiFeO3 powders by room temperature solid state precursor method is presented in this dissertation. BiFeO3 micron/nano-powders are synthesized by the heat treatment, raw material types, NaNO3- and polyethylene glycol-assisted control method. The main morphology of BiFeO3 powders synthesized by room temperature solid state precursor method is nearly spherical grain. The grain size of BiFeO3, ranging from 18 to 600 nanometers, can be effectively controlled by different heat treatment and raw materials Owing to the quantum size effect, the optical gaps and magnetic characteristics of BiFeO3 increased with the decreasing grain size. The dispersity of the particulate distinctly improved after NaNO3 was added. The magnetic characteristics of BiFeO3 increased significantly after polyethylene glycol was added. In addition, it was found that the magnetic characteristics of BiFeO3 increased and the optical band gaps decreased with nonmetal ion doping (Cl, N). (2) It is predicted that BiFeO3 has a broad prospect of application in fields such as optical electrode of solar cell and photochemical water splitting. BiFeO3 with visible light absorption and magnetic separation property can be positioned in solution by external magnetic fields.