Effect of particle morphology on the photocatalytic activity of BiFeO3 microcrystallites

Pure BiFeO₃ (BFO) microcrystallites with different morphologies were synthesized by a controlled hydrothermal process. The crystal structure, morphology and photocatalytic property of BFO microcrystallites were investigated. The results and analysis revealed that the OH^? concentration intensely affected the morphology, dimension and phase purity of BFO. Furthermore, it was found that the smallest and coarse BFO particles exhibited the lowest photocatalytic efficiency, which suggested that the particle morphology, especially defects intensely influence the photocatalytic activity of BFO, other than the particle size.     

Magnetodielectric properties of rare earth metal-doped BiFeO3 nanoparticles

Pure and rare earth metal ions (Gd³⁺, Tb³⁺, Dy³⁺)-doped BiFeO₃ nanoparticles have been synthesized by the sol–gel method. The effect of doping of rare earth metal ions on structural, magnetic, dielectric and magnetodielectric properties of synthesized nanoparticles have been investigated. Synthesized nanoparticles have been found to be possessing spherical morphology, with average particle size, 25–46 nm. Structural study confirms that 15 % mole fraction doping of the rare earth metal ions results in structural transformation from rhombohedral to orthorhombic phase. Magnetic study reveals that the synthesized nanoparticles exhibit well saturated ferromagnetic magnetic loops. Dielectric measurements show that doping of rare earth metal ions results in high dielectric constant as compared to that of pure BiFeO₃. Magnetoelectric coupling in the synthesized nanoparticles, established by performing magnetodielectric measurements, reveals that the doped nanoparticles exhibit high magnetodielectric coefficient as compared to its pure form. The high value of saturation magnetization, 5.22 emu/g, dielectric constant, 900 and magnetodielectric coefficient, 5.82 %, have been observed in Dy-doped BiFeO₃ nanoparticles. The observed trend in the properties of the synthesized nanoparticles has been explained on the basis of doping as well as size of the synthesized nanoparticles.     

Crystallisation effects on rare earth dopants in oxyfluoride glass ceramics

Transparent oxyfluoride glass-ceramic materials are of significant interest for the production of new optoelectronic devices. In this paper we report measurements of the detailed spectroscopy of rare earth dopants in both an oxyfluoride transparent glass ceramic and its glass precursor. We show that several spectroscopically different sites exist for the rare earth even in the glass precursor material, where a significant amount of the rare earth is already coordinated with fluorine. In the glass-ceramic material, these glassy fluorine-coordinated sites are replaced with crystalline sites, but a significant fraction of the rare earth ions are still within the glass phase. The fraction of rare earth ion that is incorporated into the crystalline phase is estimated from the rare earth spectroscopy, and the role of the rare earth coordination in the precursor glass is discussed.     

稀土铁酸盐的制备及光催化性能

在600℃温度下热分解配位前驱体,制备出5种稀土铁酸盐颗粒(ReFeO3,Re=Y3+、La3+、Sm3+、Gd3+和Ho3+).采用XRD、SEM、Uv-Vis DRS以及VSM等手段对所制备产物进行物相、表面形貌、能带结构以及磁性能等进行表征.XRD表明,含Y3+、La3+和Gd3+的前驱体灼烧后产物为单相正交晶系...     

Dependence of thermo-mechanical and mechanical properties of novel fluorophosphate glass on various rare earth dopants

The dependence of thermo-mechanical, and mechanical properties on various rare earth dopants (RE) including Nd₂O₃, Er₂O₃, and Yb₂O₃ in 0.4MgF₂-0.4BaF₂-0.1Ba(PO₃)₂-0.1Al(PO₃)₃ glasses (MBBA system) is systematically investigated. MBBA system doped with RE dopants presented the potential application in the field of communication and high power layer system in the previous reports. In this work, it is found that the density of the doped glass increases with an increasing of RE concentration, which could be understood in terms of cationic field strength (CFS) effect. The Knoop hardness is found to decrease with the loading time and dopant concentration due to the indentation size effect (ISE) effect. The observed decrease of thermal expansion coefficient and the increase of glass transition temperature T _g with increasing dopant concentration are elucidated in terms of the increasing number of strong covalent bonds with increasing RE dopant concentration. Those results will be of paramount importance before designing optical devices.     

稀土元素对AgCuNi合金铸态显微组织的影响

研究了稀土Y和复合稀土La、Y对AgCu-Ni合金铸态显微组织及力学性能的影响。研究结果表明,随着Y含量的增加,铸态组织晶粒尺寸减小,并由树枝晶逐渐转变为胞晶;稀土元素以化合物(AgCu)5RE形式偏聚在晶界上,当La、Y复合添加时,稀土元素呈共生态在晶界析出;随着RE含量的增加,AgCuNiRE合金显微硬度增加,当RE含量由0.6%增加到2.2%时,合金硬度值比AgCuNi合金增加了0.26~1.28倍。     

Characterization and photocatalytic activity of Y-doped BiFeO3 ceramics prepared by solid-state reaction method

Singe phase bismuth ferrite doped by yttrium (Bi_1?xY_xFeO₃, x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25) was synthesized by solid-state reaction followed by sintering. Their structural, morphological, ferroelectric, magnetic and optical properties were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), vibrating sample magnetometer (VSM) and UV–visible spectrophotometry. Rhombohedrally-distorted perovskite structure of bismuth ferrite was confirmed by XRD analysis and Rietveld refinement. Microstrain and crystallite size were analyzed using Williamson-Hall model. SEM micrographs showed agglomerated particles. The doping of yttrium into the BiFeO₃ (BFO) lattice enhanced the ferroelectric and magnetic properties and the leakage current density was reduced. The energy band gap was also decreased by increasing yttrium content, leading to an enhancement of light absorption capability. The photocatalytic activity of all samples has been evaluated by the decolorization of methyl orange (MO) under visible light irradiation. The results indicated that increasing the concentration of yttrium into the BiFeO₃ (BFO) structure improved the photodegradation up to 71%.     

稀土及硼含量对α-Fe/R2Fe14B纳米晶稀土永磁材料磁性能的影响

分析了自1993年至今国内外文献中报道的α-Fe/R2Fe14B纳米晶稀土永磁薄带的实验数据,研究了稀土含量及硼含量对材料磁性能的影响.结果表明,随稀土含量的增加,纳米晶稀土永磁薄带的矫顽力增加,剩磁趋于减小,稀土含量在8%～9%之间获得最佳的综合磁性能;较高的硼含量有利于获得高矫顽力,但不利于得到高剩磁,硼含量在5%～6%之间为宜.     

Enhanced photocatalytic activity of BiFeO3 particles by surface decoration with Ag nanoparticles

BiFeO₃ particles with different morphologies and sizes were synthesized via a hydrothermal process, where the morphology and size was tailored by using different KOH concentrations in precursor solution. The samples prepared at n(KOH) = 3, 4.5, 6, and 7.5 M are composed, respectively, of octahedron-shaped particles (500–600 nm), cube-like particles (200–500 nm), irregular spherical agglomerates (9–16 μm) formed from disk-like grains with diameter of 1.4–2.8 μm and thickness of 0.2 μm, and cuboid-shaped particles with length-to-width ratio of 1.4:1–3.5:1 and width size ranging from 80 to 280 nm. Ag nanoparticles were deposited on the surface of BiFeO₃ particles by a chemical reduction method to produce Ag@BiFeO₃ nanocomposites. The photocatalytic activity of prepared samples was evaluated by degrading rhodamine B under simulated sunlight irradiation. It is demonstrated that Ag-decorated BiFeO₃ particles exhibit an enhanced photocatalytic activity compared to bare BiFeO₃ particles. This can be explained by the effective transfer of photogenerated electrons from the conduction band of BiFeO₃ to Ag nanoparticles and hence increased availability of holes for the photocatalytic reaction. Hydroxyl radicals were detected by the photoluminescence technique using terephthalic acid as a probe molecule and are found to be produced over the irradiated BiFeO₃ and Ag@BiFeO₃ photocatalysts; especially, an enhanced yield is observed for the latter.     

稀土元素对FeCrMoCB系合金玻璃形成能力的影响

近年来,随着铁基大块非晶合金尺度不断取得新的突破,无磁非晶钢的开发和研究受到日益广泛的关注。然而,FeCrMoCB系非晶钢的玻璃形成能力很弱,仅能形成直径为1.5mm的大块非晶合金。采用铜模真空吸铸法,探讨Y、Pr、Gd、Tb等稀土元素对Fe48Cr15Mo14C15B6M2(M=RE)系合金玻璃形成能力的影响,实验结果表明,用2%(原子分数)的稀土元素Y、Pr、Gd、Tb分别替换Fe50Cr15Mo14C15B6中的Fe,能制备出一系列Fe48Cr15Mo14C15B6M2(M=RE)系非晶棒。Fe48Cr15Mo14C15B6M2(M=Pr,Y,Gd,Tb)非晶棒的最大直径依次可达3、8、12和12mm。     

稀土Er对Al-Mg合金组织和性能的影响研究

在Al-Mg合金的基础上,通过调整稀土元素Er的掺杂含量,制备了不同稀土Er掺杂量(0,0.3％,0.6％和0.9％)(质量分数)的Al-Mg合金.通过XRD、SEM、电子万能试验机和浸泡腐蚀试验研究了Al-Mg合金的晶体结构、微观形貌、力学性能和腐蚀性能.结果表明,所有Al-Mg合金的结晶性能都较好,未掺杂稀土Er的...     

The optical absorption edge of rare earth sesquisulfides and alkaline earth - rare earth sulfides

Optical band gaps were measured by diffuse reflectance spectroscopy on a series of Ln₂S₃ compounds of α, δ, ε and τ structure types and on a series of ternary sulfides MLn₂S₄ (M = Sr, Cd, Mg) of Th₃P₄, CaFe₂O₄ and spinel structure types. Sharp absorption edges are observed with band gaps ranging from 2.2 to 3.5 eV. Systematic changes occur with rare earth radii. Analysis of some of the absorption edges suggests direct forbidden transitions.     

络合物对制备纯相BiFeO_3纳米晶的影响

采用溶胶-凝胶法用聚乙烯醇(PVA)和酒石酸两种不同络合物制备了BiFeO3纳米晶。通过优化两种络合物的制备工艺,在400℃的低温下以酒石酸作络合物时,得到了纯相的BiFeO3纳米晶。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)测量分析了样品结构和形貌,研究了溶胶-凝胶制备工艺和不同络合物对BiFeO3纳米晶的形成及晶体结构的影响。     

Effect of Gd-substitution on phase transition and conduction mechanism of BiFeO3

The polycrystalline sample of (Bi_0.8Gd_0.2)FeO₃ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the sample confirms the formation of the desired compound with rhombohedral phase. The scanning electron micrograph of the sample showed uniform distribution of the plate- and rod-shaped grains. Studies of dielectric and electrical properties of the material were investigated within a wide range of temperature (25–400 °C) and frequency (1 kHz–1 MHz) using complex impedance spectroscopic method. The observation of hysteresis loop of the material confirmed that the material has a ferroelectric property at room temperature. The ac conductivity suggests that the sample obey Jonscher’s universal power law. The dc conductivity follows Arrhenius equation. Detailed studies of ac and dc conductivity show a negative temperature coefficient of resistance (NTCR) behavior of the sample.     

Structure evolution and photocatalytic activity of BiFeO3 powders synthesized by hydrothermal decomposition of metal-EDTA complexes

In the paper, the formation mechanism for pure phase BiFeO₃ (BFO) in an EDTA-assisted hydrothermal process with the presence of NaNO₂ was investigated in detail. The analysis revealed that the hydrothermal decomposition of Fe-EDTA complexes with the presence of NaNO₂ intensely influenced both the crystal structure and morphology of BFO powders. Moreover, pure BFO particles exhibited efficient photocatalytic activity under visible-light irradiation, suggesting their promising applications as photocatalysts.