尖晶石型Ni0.8Zn0.2Fe2O4纳米晶体的制备及电磁性能研究

以金属离子的柠檬酸盐为前驱体，通过sol-gel自燃烧的合成方法制备了镍锌铁氧体（Ni0．8Zn0．2Fe2O4）纳米晶体。采用FT-IR、DSC-TG、XRD、TEM波导等方法对产物以及产物的电磁性能进行了表征。结果表明，在前驱体中，金属离子与柠檬酸以络合物的形式存在，凝胶在220℃完成自燃烧反应，随着热处理温度的升高，粉体的粒径逐渐增大，纳米晶体在8-12GHz的测试条件下具有介电损耗与磁损耗，随着涂层厚度的增加，混合媒质的微波反射率逐渐增加，反射率吸收峰随着厚度的增加向低频移动。     

脉冲激光沉积制备外延Ni_(0.8)Zn_(0.2)Fe_2O_4薄膜的应变与磁性能研究

用脉冲激光沉积设备,分别在SrTiO3(001)(STO)和MgO(001)基片上外延生长了单层Ni0.8Zn0.2Fe2O4(NZF)薄膜。经X射线衍射分析,在STO和MgO基片上制备的NZF薄膜均为单一c取向的外延薄膜,由PHI扫描可知薄膜均为四重对称结构。由NZF薄膜的倒易空间图可以计算得到在STO和MgO基片上应变分别为0.0704和-0.0124。分别对不同基片上的NZF薄膜进行磁强计测量可得,在STO基片上沉积的NZF薄膜的面内和面外饱和磁化强度分别为269.6和224.78 emu/cm3,面内和面外的矫顽场分别为2.68×104和4.78×104A/m,在MgO基片上沉积的NZF薄膜的面内和面外饱和磁化强度分别为219.11和180.75 emu/cm3,面内和面外的矫顽场分别为3.46×104和5.32×104A/m。     

Mn0．8Zn0．2Fe2O4／MgAl-LDHs复合材料的磁性能和磁热效应

采用共沉淀法将纳米锰锌铁氧体粒子(Mn0.8Zn0.2Fe2O4)与镁铝双金属氢氧化物(MgAl-LDHs)进行组装合成了磁性纳米镁铝双金属氢氧化物,并通过TEM,FTIR、DTA、XRD、VSM等方法对其进行表征.样品的结构分析结果表明,复合材料具有典型的核壳结构,镁铝双金属氢氧化物被赋予磁性后并没有改变其层状结构的典型特征.样品的磁学性能和磁热性能测试结果表明,铁氧体的含量对复合材料的磁性能和磁热效应起着决定性作用;MgAl-LDHs对铁氧体粒子没有显著的磁屏蔽效应,复合材料的饱和磁化强度与铁氧体的含量呈正线性相关,而复合材料的矫顽力随MgAl-LDHs含量的增加呈现先减小后增大的趋势,但整体变化幅度很小,同时MgAl-LDHs对铁氧体粒子磁热效应的影响也极小.     

Magnetic and dielectric properties of Ni0.8Zn0.2Fe2O4/HDPE composites for high-frequency application

A low loss high-frequency magnetic composite with Ni_0.8Zn_0.2Fe₂O₄ (NZO) ultrafine particles embedded in a high density polyethylene (HDPE) matrix was fabricated by using a simple low-temperature hot-pressing technique. The magnetic and dielectric properties of the as-prepared composites were investigated in details. The results indicate that as the volume of the ceramic fillers increase, the permittivity, permeability, dielectric and magnetic loss of the composite all increase. The cut-off frequencies of the composites are all above 1 GHz. Because of the low resistivity of NZO, the dielectric losses of the composites are big and decrease with frequency below 100 MHz. Good frequency stabilities of the permittivities and permeabilities, and low dielectric and magnetic losses within the measurement range have been observed. For the composite containing 30 vol% NZO, the permittivity, dielectric loss, permeability and magnetic loss are 3.7, 0.0025, 2.2 and 0.002 at 100 MHz, respectively.     

Structural, Magnetic, and Dielectric Properties of PEG Assisted Synthesis of Mn0.5Ni0.5Fe2O4 Nanoferrites

The Mn_0.5Ni_0.5Fe₂O₄ nanoferrites with different morphology were prepared using the PEG assisted coprecipitation method. The two different iron salts were used for preparing the Mn–Ni ferrites with different morphologies by the coprecipitation air oxygenation method. Spherical and acicular nanoparticles were obtained by the calcination of the precursor. The phase, morphology, and crystallite size of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Magnetic properties were measured by the vibrating sample magnetometer (VSM). The saturation magnetization (M _s ), coercivity (H _c ) and Bohr magneton (n _B ) were found to be increased with an increase in effective anisotropy. The dielectric properties were found to decrease with the increased heterogeneity in the samples. The dielectric constant (ε′) and dielectric loss (tanδ) measured from 20 Hz to 1 GHz and variation in magnitudes show dependence on morphology of the prepared samples. Impedance spectroscopic measurements revealed that the electrical conduction in ferrite ceramics is due to resistance of grains interior.     

聚吡咯/Ni0.5Zn0.5Fe2O4复合物的合成与表征

采用超声场下原位聚合法制备聚吡咯/Ni0.5Zn0.5Fe2O4(PPy/NZFO)复合物。分别采用X射线衍射仪(XRD)、扫描电镜(SEM)、四探针测试仪和矢量网络分析仪对其结构、形貌、电性能和吸波性能进行研究。结果表明:APS/Py摩尔比为0.75的条件下可获得团聚程度较小、粒径大小比较均匀的聚吡咯颗粒。随着超声聚合反应时间的延长,聚吡咯颗粒的粒径呈现增大趋势。PPy/NZFO复合物的电导率与PPy含量成正比。复合物的吸波性能较纯PPy有很大提高,在5~20GHz频率范围内,NZFO含量为40%(质量分数)的复合物反射损耗都在-12dB以上,在18.15GHz处具有最大的反射损耗-16.76dB,-15dB有效带宽为1.65GHz。     

La0.8Pb0.2Fe0.8Ni0.2O3纳米粉体的制备及其CO气敏性能研究

采用柠檬酸法制备了多晶La0.8Pb0.2Fe0.8Ni0.2O3,并对其结构、电导特性和CO气敏特性进行了研究.结果表明,该材料属正交晶系钙钛矿结构,显示了p型半导体导电特性,并且在工作温度120～340℃范围内对CO气体均具有较高灵敏度,显示出对CO气体的良好气敏性能.     

Structural and magnetic properties of room temperature milled Co0.2Zn0.8Fe2O4 spinel oxide

We report the nanoparticle Co_0.2Zn_0.8Fe₂O₄ spinel oxide, synthesized by room temperature mechanical milling. The system is stabilized mainly in spinel oxide phase after 78 hrs milling time and no other phases have been observed from the XRD spectra of the 100 hrs milled sample. We have studied the particle size effects on structural as well as on magnetic properties by annealing the 100 hrs as milled sample at different temperatures for 12 hours. The XRD and TEM data show that the particle size decreases with increasing milling time upto 60 hrs and then show an increasing trend with milling time. The particle size also increases with annealing the 100 hrs as milled sample with better crystalline structure. It is observed that the magnetic properties of the annealed samples can be correlated with the structural change without breaking the crystal symmetry of the cubic spinel phase of Co_0.2Zn_0.8Fe₂O₄ spinel oxide. The change in the crystal structural as revealed by the XRD spectra can be associated with the non-equilibrium to equilibrium cationic distribution between tetrahedral (A) and octahedral (B) sites of the spinel structure.     

Synthesis and Magnetic Properties of Fe3O4 Nanoparticles

Magnetic Fe₃O₄ nanoparticles with size below 10 nm have been prepared by the aqueous phase coprecipitation method. The Fe₃O₄ nanoparticles show typical superparamagnetism. Comparison is made between the dispersed sample and the powder sample, and the results are discussed.     

Electrical and magnetic properties of Ni0.8Zn0.2Fe2O4/silica composite prepared by sol-gel method

Ultrafine Ni_0.8Zn_0.2Fe₂O₄ particles dispersed in silica (SiO₂) matrix are produced by sol-gel method. The powders were subjected to X-ray diffraction to confirm the formation of crystalline phases. The physical properties such as bulk density, true density, % of porosity and % of linear shrinkage were studied. The magnetic permeability as the function of frequency from 1 kHz to 13 MHz and temperatures from room temperature to 300°C were studied for samples sintered at temperature 1250°C. The AC electrical resistivity as the function of frequency and DC electrical resistivity as the function of temperature were studied. The AC-resistivity of the order of 10⁵ cm and DC-resistivity 10⁸ cm were obtained at room temperature. Microstructural features of sintered samples show the presence of ferrite grains of 1–2 m size.     

Effect of Sintering on Magnetic Properties of Ni0.55Zn0.45Fe2O4

Bulk Ni_0.55Zn_0.45Fe₂O₄ samples were obtained by sintering their nanopowder at 1100 ^°C, 1200 ^°C, and 1300 ^°C. Improvement in crystallinity on sintering was identified from increase in intensity of the XRD peaks and grain development in SEM micrographs. Saturation magnetization increased from 81.7 emu/g to 85.3 emu/g as the sintering temperature increased from 1100 ^°C to 1300 ^°C. Initial permeability increases whereas the relative loss factor, resonance frequency, and DC resistivity decreases with increasing the sintering temperature. Curie temperatures obtained from low field AC normalized susceptibility and permeability measurements are in good agreement. The DC resistivity of the samples in the present case is two orders higher than the reported values of samples prepared using conventional ceramic method.     

Synthesis and Study of Structural,Morphological and Magnetic Properties of ZnFe2O4 Nanoparticles

Superparamagnetic zinc ferrite (ZnFe₂O₄) nanoparticles were prepared by a surfactant assisted hydrothermal method and subjected to the heat treatment. The structure, vibrational, morphology, and magnetic properties of synthesized product were characterized by XRD, FT-IR, HR-SEM, and VSM measurements. XRD result confirms the formation of regular spinel structured ZnFe₂O₄ with space group of Fd3m and an average crystalline size was calculated as 21 nm and 28 nm for the samples annealed in air atmosphere at 300 °C and 600 °C. The HR-SEM image shows that the particles are in spherical shape with small aggregation. A room temperature superparamagnetic behavior was observed for both samples. The saturation magnetization (M _s) of 12.0 emu/g and 9.10 emu/g were observed for the samples annealed in air atmosphere at 300 °C and 600 °C, respectively.     

Magnetic Properties of Cu0.48Ni0.52Fe2O4 and Thermal Process of Precursor

The spinel Cu_0.48Ni_0.52Fe₂O₄ was synthesized by calcining Cu_0.48Ni_0.52Fe₂(C₂O₄)₃?5H₂O above 300 °C in air for 1.5 h. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, FT-IR, X-ray powder diffraction, and vibrating sample magnetometer. The result showed that magnetic properties of Cu_0.48Ni_0.52Fe₂O₄ were influenced by calcination temperature, and Cu_0.48Ni_0.52Fe₂O₄ obtained at 600 °C had a specific saturation magnetization of 40.0 emu?g^?1. The thermal process of Cu_0.48Ni_0.52Fe₂(C₂O₄)₃?5H₂O below 450 °C experienced two steps which involved, at first, the dehydration of the five crystal water molecules, then decomposition of Cu_0.48Ni_0.52Fe₂(C₂O₄)₃ into cubic Cu_0.48Ni_0.52Fe₂O₄ in air. In the DTG curve, two DTG peaks indicated that precursor experienced mass loss of two steps.     

Synthesis,structural and electrical properties of triethylene glycol (TREG) stabilized Mn0.2Co0.8Fe2O4 NPs

Triethylene glycol (TREG) stabilized Mn_0.2Co_0.8Fe₂O₄ NPs was synthesized by a glycothermal reaction. XRD analysis identified the product as Mn_0.2Co_0.8Fe₂O₄ with a high phase purity. Nano-sized particles with an average size of about 6–8 nm were obtained with nearly single crystalline nature with TEM analysis. Superparamagnetic-like behavior of TREG stabilized Mn_0.2Co_0.8Fe₂O₄ NPs was observed by VSM. The binding between TREG and Mn_0.2Co_0.8Fe₂O₄ NPs was investigated with FT-IR and found to be via O on the TREG and NP surface. TG analysis indicated that the Mn_0.2Co_0.8Fe₂O₄ NP content was about 40%, with a TREG-shell content to be around 60%. Overall conductivity of the nanocomposite is in the range of 10^?10 to 10^?7 S cm^?1 with a strong dependence on temperature and frequency, indicating ionic conductivity. The nanocomposite exhibited lower ?’ and ?″ compared to TREG stabilized Mn_0.2Co_0.8Fe₂O₄ NPs due to the doping of co-doping of manganese and cobalt.     

Synthesis and Magnetic Properties of Bulk Ferrites Spinels Ni0.5Zn0.5Fe2O4: Experimental an Ab-Initio Study

Polycrystalline Ni_0.5Zn_0.5Fe₂O₄ ferrites have been prepared using the solid-state reaction technique. The structure of ferrite was measured using an X-ray diffractometer (XRD). It is shown that the structure of Ni_0.5Zn_0.5Fe₂O₄ ferrites is a single spinel structure. The magnetic properties of the samples were tested at room temperature by a superconducting quantum interference device (SQUID) to determine magnetic properties versus temperature and applied magnetic field. Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), the ferromagnetic and half-metallic behaviors was observed with LDA (local density approximation) and LDA–SIC (local density approximation-self-interaction correction) approximation.     

Ce0.8Sm0.2O1.9基纳米复合材料的共沉淀合成与氧离子导电性

用化学共沉淀法制备了Ce_0.8Sm_0.2O_1.9-La_9.33Si₆O₂₆纳米复合氧离子导电材料,通过X射线衍射和透射电子显微镜对合成材料的相结构进行了分析,利用交流阻抗分析测试研究了材料的离子导电性. 结果表明,纳米复合材料的煅烧粉末的平均晶粒尺寸为20nm、烧结陶瓷体的平均晶粒尺寸为44nm;700℃时,纳米复合导电体的离子导电率为0.25Ω/cm;在整个测试温度范围内,纳米复合导电体比纯La_9.33Si₆O₂₆提高了3个以上数量级,并高于纯相Ce_0.8Sm_0.2O_1.9的导电性.     

高密度锂离子电池正极材料LiNi0.8Co0.2O2合成的研究

以二次干燥化学共沉淀法制得高密度前驱体Ni0.8Co0.2(OH)2,再与LiNO3混合经两个恒温阶段烧结(600℃恒温6h、800℃恒温24h)得到高密度LiNi0.8Co0.2O2.探讨了锂源、镍源、合成温度、合成时间等因素对产品的影响,从而优化了LiNi0.8Co0.2O2的合成工艺.所得非球形LiNi0.8Co0.2O2 粉末振实密度高达3.24g/cm3,大幅度地提高正极材料的体积比能量.X射线衍射分析表明合成的LiNi0.8Co0.2O2具有规整的层状NaFeO2结构,预示着材料具有良好的电化学性能.     

Influence of manganese dioxide and Ba2Co2Fe12O22‐additives on the magnetic power loss of Ni0.8Zn0.2Fe2O4 ferrites

Manganese dioxide and Ba₂Co₂Fe₁₂O₂₂ added Ni_0.8Zn_0.2Fe₂O₄ ferrites were prepared by solid state reaction process. The structure and magnetic properties of the ferrites were investigated by X‐ray diffractometer and magnetic flux density‐magnetic field analyzer. It was found that the magnetic loss shows increase‐decrease‐increase variation trend with the increase of manganese dioxide additive concentration, and the optimal concentration of manganese dioxide doping is about 1.2 wt.%. Compared with the sample without manganese dioxide doping, further investigation revealed that the hysteresis loss coefficient and eddy current loss coefficient decreased in 1.2 wt.% manganese dioxide doping nickel zinc ferrite, but the residual loss coefficient increased with manganese dioxide doping.