Co_(0.5)Zn_(0.5)Fe_2O_4/SiO_2磁性纳米复合粉体的制备

采用溶胶-凝胶法以正硅酸乙酯和金属硝酸盐分别作为SiO2和铁氧体的前驱体成功制得Co0.5Zn0.5-Fe2O4/SiO2磁性纳米复合粒子.利用XRD、DSC-TG、Raman和SEM研究了热处理温度和酸添加量对样品晶体结构和晶粒尺寸的影响,并用谢乐公式估算平均晶粒尺寸.最后用振动样品磁场计(VSM)对样品的磁性能进行检测.结果表明,随热处理温度的升高,样品由非晶态转变成SiO2基体中结晶较完整的尖晶石结构的单相铁氧体纳米晶,晶粒尺寸为12.65nm.晶粒尺寸随热处理温度的升高和酸添加量的增加不断变大.对材料的磁性能的研究结果表明,合成的纳米Co0.5Zn0.5Fe2O4/SiO2,其比饱和磁化强度为9.17emu/g,矫顽力为67Oe.     

Synthesis and characterization of magnetic and microwave absorbing properties in polycrystalline cobalt zinc ferrite (Co<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>) composite

In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co_0.5Zn_0.5Fe₂O₄ was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co_0.5Zn_0.5Fe₂O₄ provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material.     

High performance sintering NiCuZn ferrites absorber sheet for HF application

By using a new and simple blade casting method, a lighter, thinner and higher absorption property sintering NiCuZn ferrite electromagnetic wave absorber sheet was first demonstrated. The electromagnetic wave absorption ability was enhanced by sintered NiCuZn ferrite absorbent. The experiment results reveal that NiCuZn ferrite with thickness 0.1 mm absorber sheet achieves its maximum reflection loss value above 0.5 dB at 13.46 MHz. Meanwhile, the absorption bandwidth is larger than 1 MHz is profitable for wideband electromagnetic wave absorbing. The absorption properties could be controlled by the variation of Nickel content in the spinel lattice and the sintering temperature of NiCuZn ferrites. More homogenous microstructure of SEM micrograph and better crystalline XRD pattern may be responsible for the best absorption ability at 1,150 °C sintering temperature. The absorption properties were also successfully analyzed in this work, which took into account both the frequency at the reflection loss minimum (f _r) shift correlated with the value of inductance (L) and impedance (Z) of sintered toroidal cores and the power reflection loss (Γ) depending on ε″, μ″, and $\sqrt {\varepsilon \mu }$ , where ε and μ are complex relative dielectric permittivity and permeability, respectively, for the attenuation material. The sintering NiCuZn ferrites could merit to be potential candidates as electromagnetic attenuation materials to meet the demands for miniaturization, broader relative bandwidths at HF (3–30 MHz) and beneficial for fabrication of radio frequency identification metal tag.     

NbO3-LiNbO3无铅压电陶瓷的烧结特性和压电性能研究

采用传统陶瓷烧结工艺制备了（1-x）（K0．5Na0．5）NbO3-xLiNbO3无铅压电陶瓷，研究了陶瓷的结构、烧结特性及电性能特征．制备的（K0．5Na0．5）NbO3-LiNbO3陶瓷为单一的钙钦矿结构，室温下其相结构随LiNbO3含量增加逐渐由正交相向四方相转变，显微结构也由于LiNbO3含量的不同而表现出很大差异．与（K0．5Na0．5）NbO3陶瓷相比，（K0．5Na0．5）NbO3-LiNbO3陶瓷的烧结温度降低，烧结特性得到改善．（K0．5Na0．5）NbO3-LiNbO3陶瓷表现出优越的压电性能，其中0．94（K0．5Na0．5）NbO3—0．06LiNbO3（x=0．06）陶瓷的压电常数d33达到205pC／N，机电耦合系数kp为40．3％，kt达到49．8％．     

Ni0.5Zn0.5Nd0.02Fe1.98O4-聚苯胺纳米复合材料的制备及电磁性能（英文）

在Ni0.5Zn0.5Nd0.02Fe1.98O4纳米粒子表面原位聚合苯胺制备了Ni0.5Zn0.5Nd0.02Fe1.98O4-聚苯胺(PANI)纳米复合材料.铁氧体含量为0%、15%和30%样品的结构、形貌和电磁性能分别采用X射线衍射仪(XRD)、透射电子显微镜(TEM)和HB8510B网络分析仪进行了研究.结果表明,聚苯胺包覆层对Ni0.5Zn0.5Nd0.02Fe1.98O4的结晶度有一定影响.在X波段(8.2～12.4 GHz),复介电常数的实部随铁氧体含量的增加而减小,虚部随铁氧体含量的增加而增大.复磁导率的实部和虚部都随铁氧体含量的增加而增大.     

纳米晶锌铁氧体的聚丙烯酰胺凝胶法制备、表征及其电磁性能

采用聚丙烯酰胺凝胶法合成了尖晶石型锌铁氧体（ZnFe2O4）,采用差分扫描-热重同步分析仪（DSC-TG）,红外光谱（FT-IR）,X射线衍射（XRD）,透射电镜（TEM）和波导法对干凝胶和产物进行了表征．红外光谱显示当煅烧温度从500℃升高到700℃时,铁-氧（FPO）键的特征吸收峰从541cm^-1移动到566cm^-1;XRD表明干凝胶为无定形态,在煅烧温度为500℃、煅烧时间为2h时,凝胶形成纯相的尖晶石型纳米晶ZnFe2O4;由透射电镜可知煅烧温度为500℃、600℃和700℃时,粉体的平均粒径分别为15nm、35nm和60nm;纳米晶体ZnFe2O4在8．2～12．4GHz的测试频率范围内具有介电损耗和磁损耗随着热处理温度的升高,介电常数、介电损耗、磁导率和磁损耗明显增大．     

Synthesis, Characterization and Electromagnetic Studies on Nanocrystalline Nickel Zinc Ferrite by Polyacrylamide Gel

Nanocrystalline nickel zinc ferrite powders （Ni=Zn1-xFe2O4, A for x=0, B for x=0.2, C for x=0.5, D for x= 0.8 and E for x= 1） were synthesized by polyacrylamide gel method. X-ray diffraction （XRD）, transmission electron microscopy （TEM） and wave-guide were used to characterize the composition. The XRD results show that the dried gel powders are amorphous, and the characteristic peaks of the spinel Ni0.5Zn0.5Fe2O4 appear after the gel is calcined at 400℃ for 1 h. When the calcining temperatures are 600 and 800℃, the average grain sizes are identified by TEM to be 10 and 30 nm, respectively. The NixZn1-xFe2O4 powders have both dielectric loss and magnetic loss in the frequency range of 8.2-11.0GHz. With the increase of Ni^2＋ ions content, the dielectric parameters （ε′） and permeability （u′） of the NixZn1-xFe2O4 powders decrease while the dielectric loss （ε″）, magnetic loss （u″） and the reflection loss increase.     

Preparation and characterization of the bismuth sodium titanate (Na0.5Bi0.5TiO3) ceramic doped with ZnO

This study investigates effects of the zinc oxide (ZnO) addition and the sintering temperature on the microstructure and the electrical properties (such as dielectric constant and loss tangent) of the lead-free piezoelectric ceramic of bismuth sodium titanate (Na_0.5Bi_0.5TiO₃), NBT, which was prepared using the mixed oxide method. Three kinds of starting powders (such as Bi₂O₃, Na₂CO₃ and TiO₂) were mixed and calcined. This calcined NBT powder and a certain weight percentage of ZnO were mixed and compressed into a green compact of NBT–ZnO. Then, this green compact of NBT–ZnO was sintered to be a disk doped with ZnO, and its characteristics were measured. In this study, the calcining temperature was 800 °C, the sintering temperatures ranged from 1000 to 1150 °C, and the weight percentages of ZnO doping included 0.0, 0.5, 1.0, and 2.0 wt%. At a fixed wt% ZnO, the grain size increases with increase in the sintering temperature. The largest relative density of the NBT disk obtained in this study is 98.3% at the calcining temperature of 800 °C, the sintering temperature of 1050 °C, and 0.5 wt% ZnO addition. Its corresponding dielectric constant and loss tangent are 216.55 and 0.133, respectively.     

参杂尖晶石型镍基铁氧体的磁性能与介电性能

采用溶胶-凝胶法制备了立方晶系尖晶石型镍基铁氧体微粉Ni0.5M0.5Fe2O4（M=Zn、Mn、Cu）,采用X射线衍射仪、扫描电子显微镜、振动样品磁强计和矢量网络分析仪对粉末的结构、形貌、磁性以及电磁性能进行了表征,结果表明,三种粉末在室温下具有超顺磁性,其饱和磁化强度MS分别为76．0、59．4和54．4emu·g-1。在2—11GHz范围内,Ni0.5M0.5Fe2O4的电磁损耗角正切值tgδ随频率的增大而逐渐减小;Ni0.5M0.5Fe2O4和 Ni0.5M0.5Fe2O4的tgδ随频率的增大先增大后减小。     

Ni0.5Zn0.5Fe2O4粉末化学镀铜前后的电磁性能

本文用溶胶-凝胶自燃烧法制备了Ni0.5Zn0.5Fe2O4粉末颗粒,以甲醛为还原剂在Ni0.5Zn05Fe2O4颗粒表面进行了化学镀铜,制备了Cu/Ni0.5Zn0.5Fe2O4复合粉体.用扫描电镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)对镀铜前的Ni0.5Zn0.5Fe2O4颗粒以及镀铜后的复合纳米颗粒进行了表征.对镀铜前的Ni0.5Zn0.5Fe2O4粉体和不同镀铜量的Cu/Ni0.5Zn0.5Fe2O4复合粉体进行了电磁性能的研究,结果表明镀铜后镍锌铁氧体的吸波性能明显提高,增重量为65%的Cu/Ni0.5Zn0.5Fe2O4复合粉体在频率为11GHz处反射率可达-12dB左右.     

Ni_(0.5)Zn_(0.5)Fe_2O_4铁氧体的制备及其电磁损耗性能

以Zn(NO3)2.6H2O、Ni(NO3)2.6H2O和Fe(NO3)3.9H2O及柠檬酸为原料,采用溶胶-凝胶法制备前驱体,在1 200℃下煅烧3 h合成ZnFe2O4和Ni0.5Zn0.5Fe2O4铁氧体粉体。利用差热分析、X射线衍射、扫描电镜、透射电镜和红外光谱等测试手段对产物进行分析和表征。结果表明:ZnFe2O4和Ni0.5Zn0.5Fe2O4属于立方晶系尖晶石结构,结晶完整,晶粒大小在100 nm左右。在0.2~1.8 GHz的频率下对产品进行了电磁损耗性能测试,发现Ni0.5Zn0.5Fe2O4具有较好的电磁损耗特性。     

Cellulose-precursor synthesis of nanocrystalline Co0.5Cu0.5Fe2O4 spinel ferrites

Nanocrystalline Cu_0.5Co_0.5Fe₂O₄ powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.     

M型钡铁氧体制备及吸波特性研究

为进一步研究M型铁氧体的吸波性能,以硝酸铁、硝酸钡为原料,采用溶胶凝胶自蔓延法,制备了M型钡铁氧体纳米粉.借助XRD、TG-DTA、SEM、矢量网络分析仪对铁氧体材料的晶体结构、凝胶热分解过程、表面形貌及微波吸收特性进行了研究,同时根据传输线原理,通过理论计算预测了材料的最佳匹配厚度.研究表明:所制得的铁氧体为晶相单一的M型钡铁氧体,频率在6～18GHz,预测最佳匹配厚度为0.35cm,最小反射损耗达-13.5dB,反射损耗小于-10dB的带宽为0.7GHz,说明M型钡铁氧体具有电磁波吸收效应.     

Synthesis and Electrical Properties of Li-modified Bi_(0.5)Na_(0.5)TiO_3-BaTiO_3 Lead-free Piezoelectric Ceramics

Lead-free piezoelectric ceramics (1-y)Bi0.5(Na1-xLix)0.5TiO3-yBaTiO3 with x=0-0.125 and y=0.02-0.12 were fabricated by a solid-state reaction process, and their dielectric, piezoelectric and ferroelectric properties were investigated. The results show that the addition of Li+ significantly improves the sintering performance and piezoelectric properties of the ceramics. X-ray diffraction (XRD) patterns indicate that the ceramics possess pure perovskite structure. At room temperature, the ceramics provide hig...     

Thermomechanical Analysis of (Cu0.5Tl0.5)-1223 Substituted by Pr and La

The thermomechanical analysis (TMA) of Cu 0.5 Tl 0.5 Ba 2 Ca 2 x R x Cu 3 O 10 δ,where R=Pr and La,with 0.0≤x≤0.15,was carried out in temperature range from 450 to 1145 K.The samples were prepared by singlestep solid state reaction technique.The prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The superconductivity of the prepared samples was investigated by electrical resistivity measurement.The results showed that low substitution content enhanced the (Cu 0.5 Tl 0.5)1223 phase formation,while the higher substitution content degraded this phase.The higher superconducting transition temperatures T c were found to be 114 K and 109 K at x= 0.025 for Pr-and La-substitutions,respectively.The average linear thermal expansion coefficient increased as x increased,while the shrinkage temperature decreased as x increased.Those results were emphasized by porosity and Vickers microhardness calculations.Debye temperature θ D was calculated from the linear thermal expansion coefficient data and correlated to T c to estimate the electron-phonon coupling λ ep.     

新型溶胶-凝胶工艺制备La0.5Ca0.5MnO3薄膜及性能分析

鉴于以醇盐为原料溶胶-凝胶制备La0.5Ca0.5MnO3薄膜工艺中存在诸多苛刻因素,本文以无机盐为原料采用溶胶-凝胶工艺在SiO2/Si(100)衬底上制备了La0.5Ca0.5MnO3薄膜.并用XRD、SEM和TEM等分析手段对薄膜进行了表征,通过不同磁场下电阻-温度(R-T)曲线,研究了样品的磁电阻(CMR)效应...     

Ni0.5Co0.5Fe2O4铁氧体/氰酸酯-环氧树脂复合材料的制备和性能

采用水热法合成Ni_0.5Co_0.5Fe₂O₄铁氧体,并应用于氰酸酯-环氧树脂（CE-EP）复合材料的增韧改性,研究Ni_0.5Co_0.5Fe₂O₄铁氧体对CE-EP固化反应、力学性能及热稳定性的影响。XRD和SEM结果表明,所合成的Ni_0.5Co_0.5Fe₂O₄铁氧体结晶性好、纯净、呈块状,粒径约为20 nm。性能研究表明,Ni_0.5Co_0.5Fe₂O₄铁氧体的加入对CE和EP间的固化反应速度影响不大,且不会改变树脂基体的固化反应机制。与纯CE-EP树脂体系相比,Ni_0.5Co_0.5Fe₂O₄铁氧体/CE-EP复合材料在保持CE-EP玻璃化转变温度（T_g）的基础上明显改善了其韧性,当Ni_0.5Co_0.5Fe₂O₄铁氧体质量分数为3wt%时,其冲击强度和弯曲强度达到最大值,较纯CE-EP树脂基体分别提高了65%和30.3%;但其热分解温度略有降低,可能是由于Ni_0.5Co_0.5Fe₂O₄铁氧体对CE-EP树脂基体高温分解的催化作用造成的。      

Preparation, magnetic and microwave absorption properties of La0.5Sr0.5MnO3/La(OH)3 composites

La_0.5Sr_0.5MnO₃/La(OH)₃ composites with different weight ratio of La_0.5Sr_0.5MnO₃ particles and La(OH)₃ nanowires have been prepared by tuning the reaction time under hydrothermal conditions. The structure, morphology and magnetic properties have been investigated. Additionally, by the measurements of the complex permittivity, permeability and microwave absorption properties in the frequency range of 1-12 GHz, the results shown that the weight ratio of La(OH)₃ nanowires has great influence on reflection loss. Excellent absorption property can be obtained when the ratio is 1.4%, which is attributed to the enhanced electromagnetic match as well as the proper dielectric loss and magnetic loss. The enhanced electromagnetic match is originated from the improved frequency dispersion of the complex permittivity and permeability due to the presence of dielectric La(OH)₃ nanowires.     

Enhanced microwave absorption performance of graphene/doped Li ferrite nanocomposites

In the present study, Microwave absorbing Li-Sr, Li-Co ferrite nanoparticles and RGO/Li-Sr, RGO/Li-Co ferrite nanocomposites containing Li ferrite and reduced graphene oxide (RGO) were synthesized to further improve the microwave absorption performance of Li ferrite nanoparticles (LiFe₅O₈). The Li-Sr and Li-Co nanoparticles were synthesized by thermal treatment method, the RGO/Li-Sr and RGO/Li-Co nanocomposites were obtained by a polymerization method and were characterized by different techniques. The electromagnetic wave absorption properties of the samples were evaluated by vector network analyzer (VNA) in the frequency range of 2–18 GHz. The magnetic and dielectric loss, impedance matching, and electromagnetic wave absorption of the samples are significantly improved through the addition of RGO. Experimental results revealed that the RGO/Li-Co nanocomposite considerably increased microwave absorption. The minimum reflection loss (RL) of RGO/Li-Co also was found to reach −46.80 dB at the thickness of 3 mm and the effective absorption bandwidth (≤-10 dB) amounted to 6.80 GHz (from 10.52 to 17.32 GHz), which was much higher in comparison with pure Li and Li-Co ferrites nanoparticles. Due to the synergistic effect between magnetic loss and dielectric loss and the good impedance matching, the RGO/Li-Co nanocomposite may be regarded as a new candidate for microwave absorbing materials characterized with a broad effective absorption bandwidth at thin thicknesses.     

One-dimensional SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers and enhancement magnetic property

SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers of diameters about 100 nm with mass ratio 1:1 have been prepared by the electrospinning and calcination process. The SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrites are formed after calcined at 700 degrees C for 2 hours. The composite ferrite nanofibers are fabricated from nanosized Ni(0.5)Zn(0.5)Fe2O4 and SrFe12O19 ferrite grains with a uniform phase distribution. The ferrite grain size increases from about 11 to 36 nm for Ni(0.5)Zn(0.5)Fe12O4 and 24 to 56 nm for SrFe12O19 with the calcination temperature increasing from 700 to 1100 degrees C. With the ferrite grain size increasing, the coercivity (Hc) and remanence (Mr) for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers initially increase, reaching a maximum value of 118.4 kA/m and 31.5 Am2/kg at the grain size about 40 nm (SrFe12O19) and 24 nm (Ni(0.5)Zn(0.5)Fe2O4) respectively, and then show a reduction tendency with a further increase of the ferrite grain size. The specific saturation magnetization (Msh) of 63.2 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers obtained at 900 degrees C for 2 hours locates between that for the single SrFe12O19 ferrite (48.5 Am2/kg) and the single Ni(0.5)Zn(0.5)Fe2O4 ferrite (69.3 Am2/kg). In particular, the Mr value 31.5 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers is much higher than that for the individual SrFe12O19 (25.9 Am2/kg) and Ni(0.5)Zn(0.5)Fe2O4 ferrite (11.2 Am2/kg). These enhanced magnetic properties for the composite ferrite nanofibers can be attributed to the exchange-coupling interaction in the composite.