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1.
向军  宋福展  沈湘黔  褚艳秋 《物理学报》2010,59(7):4794-4801
采用溶胶-凝胶法结合静电纺丝技术制备了Ni0.5Zn0.5Fe2O4/SiO2复合纳米纤维.利用热重-差热分析、X射线衍射、场发射扫描电镜、高分辨透射电镜和振动样品磁强计研究了前驱体纤维的热分解及相转化过程以及焙烧温度和SiO2含量对目标纳米纤维的相组成、微观结构、形貌及磁性能的影响.结果表明,在450 ℃焙烧时,立方尖晶石结构已基本形成.随着焙烧温度由450 ℃升高到100  相似文献   

2.
向军  沈湘黔  宋福展  刘明权 《中国物理 B》2009,18(11):4960-4965
NiZn ferrite/polyvinylpyrrolidone composite fibres were prepared by sol–gel assisted electrospinning.Ni0.5Zn0.5Fe2O4 nanofibres with a pure cubic spinel structure were obtained subsequently by calcination of the composite fibres at high temperatures.This paper investigates the thermal decomposition process,structures and morphologies of the electrospun composite fibres and the calcined Ni0.5Zn0.5Fe2O4 nanofibres at different temperatures by thermogravimetric and differential thermal analysis,x-ray diffraction,Fourier transform infrared spectroscopy and field emission scanning electron microscopy.The magnetic behaviour of the resultant nanofibres was studied by a vibrating sample magnetometer.It is found that the grain sizes of the nanofibres increase significantly and the nanofibre morphology gradually transforms from a porous structure to a necklace-like nanostructure with the increase of calcination temperature.The Ni0.5Zn0.5Fe2O4 nanofibres obtained at 1000 C for 2 h are characterized by a necklace-like morphology and diameters of 100–200 nm.The saturation magnetization of the random Ni0.5Zn0.5Fe2O4 nanofibres increases from 46.5 to 90.2 emu/g when the calcination temperature increases from 450 to 1000 C.The coercivity reaches a maximum value of 11.0 kA/m at a calcination temperature of 600 C.Due to the shape anisotropy,the aligned Ni0.5Zn0.5Fe2O4 nanofibres exhibit an obvious magnetic anisotropy and the ease magnetizing direction is parallel to the nanofibre axis.  相似文献   

3.
Nanocrystalline Zn0.5Mn0.5Fe2O4 was synthesized through the pyrolysis of polyacrylate salt precursors prepared via in situ polymerization of the metal salts and acrylic acid. The pyrolysis behavior of the polymeric precursors was studied by use of thermal analysis. The as-obtained product was characterized by powder X-ray diffraction (XRD), transmission electron microscope (TEM), electron diffraction (ED) pattern, scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) analysis. The results revealed that the particle size is in the range of 15–25 nm for Zn-Mn ferrites with good crystallinity. Magnetic properties of the sample at 300 K were measured using a vibrating sample magnetometer, which showed that the sample exhibited characteristics of superparamagnetism.  相似文献   

4.
The microwave dielectric properties of La1-xBx(Mg0.5Sn0.5)O3 ceramics were examined with a view to their exploitation for mobile communication. The La1-xBx(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La0.995B0.005(Mg0.5Sn0.5)O3 ceramics revealed no significant variation of phase with sintering temperatures. A maximum apparent density of 6.58 g/cm3, a dielectric constant (εr) of 19.8, a quality factor (Q × f) of 41,800 GHz, and a temperature coefficient of resonant frequency (τf) of −86 ppm/°C were obtained for La0.995B0.005(Mg0.5Sn0.5)O3 ceramics that were sintered at 1500 °C for 4 h.  相似文献   

5.
采用固相合成工艺,制备了Bi05Ba05Fe05Ti049Nb001O3(BBFTN)热敏陶瓷,借助X射线衍射仪、扫描电子显微镜、阻温测试仪和交流阻抗谱考察其微结构、直流电阻、介电特性、阻抗和电学模量方面的电学性能. 结果表明:BBFTN材料依然为立方钙钛矿结构,平均晶粒尺寸约为10 μm,晶格常数相对于BaTiO3的晶格常数有所变大;室温电 关键词: 05Ba05Fe05Ti049Nb001O3')" href="#">Bi05Ba05Fe05Ti049Nb001O3 微结构 电学性能  相似文献   

6.
The [TMA]2Zn0.5Cu0.5Cl4 hybrid material was prepared and its dielectric spectra were measured in the 10−1 Hz-106 Hz frequency range and 200-305 K temperature interval. The dielectric permittivity showed a ferroelectric-paraelectric phase transition at 293 K. Double relaxation peaks are observed in the imaginary part of the electrical modulus, suggesting the presence of grain and grain boundary in the sample. The frequency dependent conductivity was interpreted in term of Jonscher's law: σ(ω)=σdc+n. The temperature dependent of the dc conductivity (σdc) was well described by the Arrhenius equation: σdcT=σo×exp(−Ea/kT).  相似文献   

7.
The sol was obtained by sol-gel method. Then, the sol was dripped onto the absorbent cotton template. The gel was obtained after the evaporation of water. Strontium ferrite microtubules were prepared after carrying out calcination process at different temperatures. The phase, morphology and particle diameter and the magnetic properties of samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM), respectively. The effects of Fe3+/Sr2+ mole ratio and calcination temperature on the crystal structure, morphology and magnetic properties of ferrite microtubules were studied. The external diameters of obtained SrFe12O19 microtubules were found to range between 8 and 13 μm; the wall thicknesses ranged between 1 and 2 μm. When the Fe3+/Sr2+ mole ratio and the calcination temperature were 11.5 and 850 °C, respectively, the coercivity, saturation magnetization and remanent magnetization for the samples were 7115.1 Oe, 70.1 and 42.4 emu/g, respectively. The mechanism of the formation and variation in magnetic properties of the microtubules were explained.  相似文献   

8.
Nanoplates of the MgAl2O4 spinel doped with Eu3+ ions were prepared by a microwave assisted hydrothermal method. Structural properties of the precursor calcined at 700 and 1000 oC powders were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). According to the obtained XRD patterns the formation of single-phase spinels after calcination was confirmed. The average spinel particle size was determined to be 11 nm after calcination at 700 °C and it increased up to 14 nm after calcination at 1000 °C. The photoluminescent properties of prepared powders with different Eu3+ ion concentrations (0-5% mol) were investigated using excitation and emission spectroscopy at room and low temperatures (77 K).  相似文献   

9.
Nanocrystalline octahedra of cobalt ferrite CoFe2O4 powders were synthesized using the organic acid precursor route. The effect of the calcination temperature, Fe3+/Co2+ molar ratio, calcination time and type of organic acid (oxalic, benzoic and tartaric acids) on the formation, crystallite size, microstructure and magnetic properties was studied systematically. The Fe3+/Co2+ molar ratio was varied from 2 to 1.739 while the annealing temperature was controlled from 400 to 1000 °C for various periods from 0.5 to 2 h. The resulting powders were investigated using X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). XRD results indicate that a well crystallized, single spinel cobalt ferrite phase was formed for the precursors annealed at 600-800 °C for 2 h, using oxalic and tartaric acids as precursors for Fe3+/Co2+ molar ratio 1.818. The crystallite size of as-formed powders was in the range of 38.0-92.6 nm at different operating conditions. The calcination temperature and Fe3+/Co2+ molar ratio have a significant effect on the microstructure of the produced cobalt ferrite. The microstructure of the produced powders was found to be octahedra-shaped. The crystalline, pure cobalt ferrite powders with magnetic properties having a maximum saturation magnetization (76.1 emu/g) was achieved for the single phase at Fe3+/Co2+ molar ratio 1.818 and annealing temperature of 600 °C for 2 h using tartaric acid precursor.  相似文献   

10.
(In1−xFex)2O3 (x = 0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In1−xFex)2O3 powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In1−xFex)2O3 samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe2+ and Fe3+ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49-1.73 μB/Fe and the Curie temperature around 783 K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe2+ and Fe3+ ions via an electron trapped in a bridging oxygen vacancy.  相似文献   

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