BaFe12O19/Ni0.6Zn0.4Fe2O4复合材料的磁性能研究

采用两步溶胶-凝胶法,分别在850℃,950℃和1050℃下成功制备了BaFe12O19/Ni0.Zn0.4Fe2O4复合材料,利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、振动样品磁强计(VSM)对样品的化学成分、结构、形貌、磁性能进行了表征.结果表明,钡铁氧体大部分呈片状,Ni0.6Zn0.4Fe2O4呈颗粒状分散在钡铁氧体周围.与850℃制备的钡铁氧体和镍锌铁氧体纯相纳米粉体相比,850 ℃制备的BaFe12O19/Ni06Zn04Fe2O4复合粉体的矫顽力和剩余磁化强度介于BaFe12O19和Ni0.6Zn0.4Fe2O4之间;饱和磁化强度(Ms=55.61 emu/g)比钡铁氧体(Ms=53.33emu/g)和镍锌铁氧体(Ms=54.13 emu/g)的都有提高.不同煅烧温度制备的BaFe12O19/ Ni0.6Zn0.4Fe2O4复合粉体,当烧结温度为950℃时饱和磁化强度最大(M =64.84 emu/g);是一种性能优良的磁性材料.     

Synthesis and magnetic properties of the SiO2–BaFe12O19 glass–ceramic composites

Samples of the magnetic glass–ceramics SiO₂–BaFe₁₂O₁₉ were obtained from mixtures of Fe₂O₃–BaSO₄–SiO₂–Na₂CO₃–CaCO₃ following a two-step route. The samples were characterized using XRD analysis and scanning electron microscopy, and their room temperature magnetization hysteresis loops were measured. It was found that the magnetic phase was completely developed in the precursor BaFe₁₂O₁₉ material when it was calcinated above 1000 °C. The size of the particles of the BaFe₁₂O₁₉ phase depends on the thermal treatment conditions and on the SiO₂ concentration. The magnetic data showed that the high value of the coercive magnetic field is preserved despite the fact that both the remanent and the saturation magnetizations diminish substantially.     

LiFe5O8 and BaFe12O19 Fine Particles Crystallised in a Glassy Matrix

We investigated the magnetic and microstructure properties of the Fe₂O₃ - Li₂O - B₂O₃ and Fe₂O₃ - BaO - B₂O₃ - Sb₂O₃ glass strips (with dimensions 50 mm long, 6 mm wide and about 30-100 mikrometer thick) subjected to various heat treatments. The irreversible structure changes produced by heat treatments, were investigated by X-ray diffraction and magnetic measurements. The magnetic behaviour is discussed in terms of the evolution of the size of LiFe₅O₈ and BaFe₁₂O₁₉ crystals dispersed in the glassy matrix, with thermal annealing.     

Structural and magnetic properties of nanometric Zn0.5Co0.5Fe2O4 prepared by hydrothermal method

ABSTRACT

The study of the structural, morphology and magnetic properties of Zn_0.5Co_0.5Fe₂O₄ ferrite is the objective of this work. The sample was prepared by hydrothermal method and was characterized by X-ray diffraction (XRD), (SEM) and (TEM) micrographs and magnetization measurements.

The magnetic hysteresis loops, field cooling (FC) and zero field cooling (ZFC) curves, in temperature range (0-400K), were measured using XL-SQUID magnetometer and the values of blocking temperatures (T_B) were determined. The results indicated that Zn_0.5Co_0.5Fe₂O₄ sample were formed in a single spinel phase and gives the value for the lattice parameter (8.3952 Å) and nanosizes of particles (13.8 nm) were compared with these obtained from ZnFe₂O₄ sample prepared also by synthesis method (8.4261 Å and 14 nm). Although, the superparamagnetic behaviour for Co-Zn ferrite has observed at 350K with a blocking temperature (T_B = 300K), that is maximum at the value obtained in the case of Zn-ferrite (T_B = 12K).     

Magnetic properties and X‐ray photoelectron spectroscopy of nanocrystalline Ho3Al5O12

Nanocrystalline holmium aluminium garnet (Ho₃Al₅O₁₂) has been prepared for the first time by modified Pechini's reaction after sintering the precursor gel at 1223 K. The nanomaterial has been characterized by X‐ray diffraction (XRD), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). The XRD pattern confirms the formation of single‐phase Ho₃Al₅O₁₂; the average size of the nanoparticles has also been determined. X‐ray photoelectron spectroscopy (XPS) has been used to study the chemical composition and bonding in the as‐prepared samples. The binding energies of core‐level electrons in Ho, Al and O in the title material have been found slightly shifted compared to the values of the respective elements. DC magnetic susceptibility has been measured in the temperature range 2 – 260 K. Low effective magnetic moment of Ho³⁺, μ_eff = 1.35 µ_B and Weiss constant have been derived from the inverse magnetic susceptibility–temperature linear plot. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

单分散BaFe12-xCuxO19纳米颗粒磁性能及穆斯堡尔谱分析

采用水热法制备BaFe12-xCuxO19(x=0、0.2、0.4、0.6、0.8)钡铁氧体,探讨Cu2掺杂量对纳米BaFe12O19微观结构以及磁性能的影响.穆斯堡尔光谱分析结果显示,Cu2可以定量可控的掺入到BaFe12O19的晶格中.利用X射线衍射仪(XRD)和扫描电镜(SEM)对不同掺杂量的样品进行表征,结果表明,800 ℃热处理可以明显提高BaFe12O19纳米颗粒的结晶性,并随着Cu2掺入量的增多BaFe12O19的晶粒尺寸逐渐增大.从磁测量分析结果可以得知,适当掺入Cu2可以降低BaFe12O19的矫顽力与饱和磁化强度,使得BaFe12O19纳米颗粒开始从硬磁性能向软磁性能转变.     

Optical and Photocatalytic properties of Mn‐doped CuO nanosheets prepared by hydrothermal method

Mn‐doped CuO nanosheets were prepared through a hydrothermal method to enhance their photocatalytic property. The structural and morphological features were monitored by using X‐Ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) with energy dispersive spectroscopy (EDS). UV‐vis absorption spectra showed the enhance absorption performance both in UV and visible light region. The band gaps were also calculate and the minimum value was 1.25 eV. The photocatalytic activity was investigated by the degradation of methylene blue (MB), which indicated that the photoactivity of samples depended on the amount of Mn²⁺ incorporated into the CuO lattice. The improved performance of photocatalysts can be attributed to enhanced light absorption and lower electron‐hole recombination.     

水热法制备SrFe12O19铁氧体粉末及其烧结后结构和磁性能研究

采用水热法合成了M型SrFe12O19铁氧体粉末,并对其烧结前后的结构和磁性能进行了研究.实验发现,无论烧结前还是后样品都是单相铁氧体结构.烧结后,样品的矫顽力和饱和磁化强度分别从42.9 kA/m和48.1 emu/g显著增加到237.8 kA/m和64.9 emu/g,这与高温烧结后其晶粒的长大密切相关.实验还发现,烧结后样品中存在着剩磁增强效应,其原因可归于样品中不同磁硬度的纳米晶相之间的磁耦合作用.     

Optical properties of flower‐like CdS prepared by a hydrothermal method with SDBS as surfactant

In this article, flower‐like CdS structures have been prepared by a hydrothermal method with SDBS as surfactant. The influences of different experimental conditions on the morphologies, UV‐Vis and fluorescence properties of CdS have been investigated. The performances of CdS have been analyzed by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet‐visible (UV–Vis) and room‐temperature photoluminescence (PL). The XRD result indicates that the flower‐like CdS structures are of hexagonal phase. The FESEM results indicate that the main role of SDBS is to make the CdS crystals assemble together to form the flower‐like structures. The UV–Vis results show CdS has a strong absorption in the ultraviolet region and visible‐light region. The PL results show CdS has two emission peaks, respectively at 461 nm and 553 nm. The growth mechanism for the formation of flower‐like CdS structures is also described.     

Magnetic properties of Fe-Co-Nd-Y-B magnet prepared by suction casting

The magnetic properties of Fe_67−xCo₁₀Nd₃Y_xB₂₀ (x = 0, 2, 6, 10) alloys prepared by suction casting had been investigated. It was found that a small addition of Y (6%) was very effective in improving glass-forming ability (GFA) of Fe-Co-Nd-Y-B alloys. The as-cast Fe₆₁Co₁₀Nd₃Y₆B₂₀ alloy presented soft magnetic behavior. However, the alloy showed the hard magnetic behavior due to exchange coupling between soft and hard magnetic phases after annealing at 948 K for 30 min. The results provide a promising approach for the production of bulk magnets by the simple process of copper mold casting and subsequent heat treatment.     

Ba2Ti9O20-BaFe12O19复合陶瓷电磁性能的研究

本文采用流延成型法制备2-2型Ba2Ti9O20-BaFe12O19复合陶瓷。通过扫描电镜、能量散射光谱仪、X射线衍射、振动样品磁强计对复合陶瓷界面微观结构及磁、电性能进行了分析。结果表明:复合陶瓷的介电常数和介电损耗均大于单相Ba2Ti9O20,饱和磁化强度、剩余磁化强度均小于单相BaFe12O19,矫顽力大于单相BaFe12O19。随着烧结温度的升高,复合陶瓷的介电常数先增加后减小,介电损耗的变化则相反;饱和磁化强度、剩余磁化强度和矫顽力减小。在1180℃烧结4 h的复合陶瓷具有适合的磁、电性能:εr=115,tanδ=0.0054,Ms=21.9 A.m2/kg,Mr=12.5 A.m2/kg和Hc=63.0 kA/m。     

New data on the physical properties of Y3Al5O12-based nanocrystalline laser ceramics

Microhardness and fracture toughness of highly transparent Y₃Al₅O₁₂-and Y₃Al₅O₁₂: Nd³⁺-based nanocrystalline ceramics are measured for the first time. For the Y₃Al₅O₁₂: Nd³⁺ laser ceramics, the use of a longitudinal scheme with a diode-laser pumping at a wavelength of 1.3186 mm (⁴ F _3/2 → ⁴ I _13/2 channel) enabled one to attain an output power of continuous-wave lasing of ～3.7 W with 35% efficiency.     

Formation and properties of Fe-based amorphous/nanocrystalline alloy coating prepared by wire arc spraying process

Wire arc spraying process was used to deposit FeBSiCrNbMnY amorphous/nanocrystalline alloy coating onto stainless steel substrate. The microstructure of the coating was characterized by using X-ray diffraction (XRD), scanning election microscopy (SEM) equipped with energy dispersive X-ray analysis (EDXA) and transmission electron microscopy (TEM). The coating is about 500 μm in thickness with fully dense and low porosity. The microstructure of the coating is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of α Fe, Cr nanoscale particles with a scale of 30–60 nm in a residual amorphous matrix region. The formation mechanism of the amorphous and nanocrystalline alloy was discussed. Mechanical properties, such as microhardness and wear resistance of the coating were also analyzed. The Vickers hardness of the coating is around Hv = 900–1050. The relatively wear resistance of the amorphous/nanocrystalline alloy coating is about 3× than that of crystalline structure 3Cr13 martensite stainless steel coating under the same wear testing condition. The FeBSiCrNbMnY amorphous/nanocrystalline alloy coating has high microhardness and excellent wear resistance.     

Structure and properties of nanocrystalline Cu70Fe18Co12 obtained by mechanical alloying

Cu₇₀Fe₁₈Co₁₂ alloy is prepared by mechanical alloying of pure Cu, Fe, Co powder using a high energy ball mill, with increasing milling time ranging from 4 to 8, 24, 36 and 54 h. The variation of the morphology and the elemental distribution were measured at these different stages on various grains of the alloy using a scanning electron microscope with a dispersive energy analyzer. Atomic clusters of iron were observed on some grains after 8 h of milling, confirming the non-homogenisation of the powder at this stage. Beyond 12 h, the homogenisation is ensured over a volume of one cube micron. Microstructural changes during the mechanical alloying have been studied by X-ray diffractometry (XRD) and Mössbauer spectroscopy. X-ray diffraction measurements confirm the dissolution of iron and cobalt phases in the FCC matrix of copper after 24 h of milling with increase of the structural parameter. This same dissolution was also measured by Mössbauer spectroscopy, confirming that after 4 h of milling the CuFe phase begins to form and iron dissolution is incomplete with partial amount of alpha Fe phase surviving after 36 h of milling.     

Magnetic properties of ferromagnetic ultrafine particles prepared by vacuum evaporation on running oil substrate

Ultrafine particles of ferromagnetic metals (Fe, Co and Ni) were prepared by the vacuum evaporation onto a running oil substrate. Particles thus obtained were suspended in the oil and their average diameter was about 25 Å. An electron diffraction analysis indicated that the particles were oxidized and the main component was Fe₃O₄, CoO and NiO for Fe, Co and Ni fine particles, respectively. From magnetic measurements in the temperature range between 4.2 and 300 K, the main magnetic behavior of the fine particles can be explained in terms of the superparamagnetism or superantiferromagnetism. Furthermore, it was concluded that the Fe₃O₄ particles may be covered with several atomic layers of α-Fe₂O₃. For CoO and NiO particles, existence of an imperfect oxide structure was required besides the main components in order to explain the magnetic behavior.     

Multi‐factors on photocatalytic properties of Y‐doped Bi2WO6 crystallites prepared by microwave‐hydrothermal method

Different contents of Y‐doped Bi₂WO₆ crystallites were synthesized by a microwave‐hydrothermal method. The photocatalytic properties with different contents of Y‐doped Bi₂WO₆ crystallites were studied. The Y‐doped Bi₂WO₆ crystallites were also characterized by XRD, EDX, SEM and UV‐vis DRS and the multi‐factors on photocatalytic properties of Y‐Doped Bi₂WO₆ crystallites were discussed. The results indicate that Y³⁺ replacing Bi³⁺ enters into the Bi₂WO₆ lattice, producing a degree of Bi₂WO₆ lattice distortion. It also has an impact on the crystallinity of Bi₂WO₆ and the band gap is from 2.49 eV to 2.71 eV. The photocatalytic results show that when the content of Y doping becomes 10%, the degradation rate of rhodamine B is above 90% after 40 min irradiation, which shows that doping the proper rare earth ions is conducive to the photocatalytic properties of Bi₂WO₆ crystallites.     

Preparation and reactivities of composite nanocrystalline solids prepared by mechanical alloying

The formation of Fe---SiC composite nanocrystalline solids through ball milling is reported. The effects of mechanical deformation, crystallite size and gaseous elements on the solid state reaction between Fe and SiC are also investigated. The formation of Fe₃C after a long milling time is attributed to the kinetics of the reaction between nanocrystalline Fe and SiC.     

Refractive indices of laser nanocrystalline ceramics based on Y3Al5O12

Refractive indices of the nanocrystalline Y₃Al₅O₁₂ ceramic and a garnet single crystal of the same composition have been measured. In the visible and near IR range (0.4–1.064 μm), the prism method was used; in the medium IR range (2–6.2 μm), the interference method with the use of thin plates was applied. The refractive indices of these crystalline materials are practically the same over the entire spectral range studied and are described by the approximate formula proposed earlier for a single crystal. The parameters of the continuos-wave lasing in the nanocrystalline Y₃Al₅O₁₂ ceramic doped with Nd³⁺ and Yb³⁺ ions measured recently are presented.     

CIS and CIGS nanomaterials prepared by solvothermal method and their spectral properties

Uniform CIS and CIGS nanomaterials were successfully synthesized by a simple amino‐based assisted solvothermal technique using PVP‐30 as the surfactant. The influence of surfactant, temperature and Ga amount on the structure, morphology, phase and spectral property was analyzed in detail. The results show that CIS and CIGS nanomaterials with 40∼70 nm in diameter can be gained at 200 °C for 24 h. PVP‐30 surfactant can greatly improve the dispersion characteristics of particles. XRD pattern shows that the “three peaks” obviously shift to bigger 2θ after gallium implantation because of lattice contraction. EDAX and Raman show that the final product is close to CuIn_0.7Ga_0.3Se₂. The possible reaction mechanism has also been explained in detail. UV‐vis‐NIR spectra show that the absorption peak and absorption edge of CIGS with 1.278 eV bandgap obviously shift to a lower energy compared to CIS with 1.051 eV bandgap, which shows the potential application in enhanced conversion efficiency.