溶胶-凝胶法制备La1-xSrxMnO3及其电磁性能研究

采用溶胶凝胶法,制备了La_1-xSr_xMnO₃(LSMO)纳米微粉。探究了Sr^₂₊的掺杂量对LSMO晶体结构、磁学性质、电磁特性和微波吸收性能的影响。结果表明,随Sr^₂₊含量的升高,样品的晶格常数和Mn-O-Mn键角增大,平均晶粒尺寸逐渐下降,样品出现从反铁磁性向铁磁性的转变,复介电常数呈先增大后减小的趋势。在2~18GHz内,x=0的样品在厚度为2mm时有最佳吸波效果,反射率小于-10dB对应的有效吸波频段为12.5~18GHz;Sr^₂₊的掺杂可使吸波频段有效的向低频移动,在X波段内,x=0.2的样品在厚度为2.3mm时的有效带宽达2.6GHz,证明LSMO是一种性能优异的介电损耗型吸波材料。     

Optical properties of buffer and superconducting layers of the YBa2Cu3O7 ?δ/La1.75Ba0.25CuO4/La0.8Ba0.2MnO3 heterostructure for second-generation superconducting cables on an Ni5% W tape

An epitaxial YBa₂Cu₃O_{7 − δ}/La_1.75Ba_0.25CuO₄/La_0.8Ba_0.2MnO₃ heterostructure has been obtained on a biaxially textured tape of an Ni5% W alloy. It is shown that when films of a buffer layer of La_0.8Ba_0.2MnO₃ applied onto a tape of an Ni alloy in a reducing atmosphere are annealed in an oxygen atmosphere it is the compensation of oxygen vacancies that plays the dominant role in the formation of optical and magnetooptical properties of the layer, rather than stresses at the film-substrate interface. The shape of the reflection spectrum of the buffer layer after annealing corresponds to that of an La_0.8Ba_0.2MnO₃ single crystal, which indicates that the oxygen content is close to the stoichiometric one. The temperature dependences of the transverse Kerr effect and coefficient of light reflection of the films at a fixed wavelength can be used for the evaluation of T _c and the temperature of the optical response of the metal-insulator transition of the buffer layer on the basis of lanthanum manganite. Original Russian Text ? O.Yu. Gorbenko, A.R. Kaul’, Yu.P. Sukhorukov, E.A. Gan’shina, S.V. Samoylenkov, N.N. Loshkareva, A.V. Telegin, O.V. Melnikov, O. Stadel, 2007, published in Fizika Metallov i Metallovedenie, 2007, Vol. 104, No. 6, pp. 578–585.     

Synthesis of nano-structured La0.8Ba0.2MnO3 perovskite via a mechano-thermal route

In this study, barium-doped lanthanum manganite, La_0.8Ba_0.2MnO₃, was synthesized via a mechano-thermal route employing high energy ball milling and subsequent heat treatment. The structural evolution, morphology and thermal behaviour of the powders were evaluated using XRD, FESEM, and DTA/TGA, respectively. DTA/TGA results showed that the calcination temperature of the carbonates significantly decreased by increasing the milling time. The results revealed that single phase perovskite was formed at 900 °C in a milled sample for 2 h and this temperature decreased to 600 °C by increasing the milling time to 30 h. The mean crystallite size also decreased from 32 to 20 nm by increasing the milling time from 2 to 30 h. The reaction sequence of La_0.8Ba_0.2MnO₃ formation via the mechano-thermal route is proposed using XRD and DTA/TGA results. FESEM micrographs showed that the mean particle size of the perovskite phase is increased slightly from 30 to 40 nm by increasing the heat treatment temperature from 600 to 900 °C.     

Direct production of porous cathode material (La1−x Sr x MnO3) using a reactive DC thermal plasma spray system

The cathode material (La_0.8Sr_0.2MnO₃) in solid oxide fuel cells (SOFCs) was plasma sprayed on mild steel in a reactive DC thermal plasma spray process. This high-speed process of depositing thin films for the components of SOFCs was examined experimentally. The results showed that a coating layer of La_0.8Sr_0.2MnO₃ with a particular porosity could be obtained directly using both prereacted La_0.8Sr_0.2MnO₃ and mixed raw materials (La₂O₃, SrCO₃, and MnO or MnCO₃) as feed materials with or without a pore former. The heat treatment of the plasma coating material at 1073 K (800 °C) for 3 h significantly enhanced the desired crystallization of La_0.8Sr_0.2MnO₃ in the coated material.     

Sr0.8Re0.2Fe11.8Co0.2O19(Re=La,Nd)的制备、表征及吸波性能

采用溶胶凝胶法,制备Sr0.8Re0.2Fe11.8Co0.2O19(Re=La,Nd)复合铁氧体。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表征粉体的结构及电磁性能。结果表明:得到的粉体为纯净的磁铅石型铁氧体,La3+掺杂样品的各项性能明显改善。在室温条件下,稀土离子掺杂后样品的Ms受到稀土离子掺杂的影响较小,Hc则明显提高;La^3+掺杂样品和Nd3+掺杂样品的Ms值接近,前者的Hc值则明显强于后者的,Sr0.8La0.2Fe11.8Co0.2O19的Ms和Hc分别为58.08A m^2/kg和362.0kA/m。稀土离子掺杂使铁氧体样品的复介电常数(ε′和ε″)增大,与Nd3+掺杂样品相比,La3+掺杂样品的介电损耗和磁损耗改善更为明显。利用传输线理论优化设计时发现,在1.2~2.4 mm之间,随着厚度的增加,Sr0.8La0.2Fe11.8Co0.2O19的反射率峰值先减少后增加,逐渐向低频移动;在厚度为2.0 mm时,其反射率峰值达到最小值为27.8 dB(11.8 GHz),小于10 dB的吸波带宽为5.2 GHz(9.5~14.7 GHz)。     

Development of a cathode layer (La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript>) in a solid Oxide fuel cell using a reactive plasma spray

A porous cathode layer (La_0.8Sr_0.2MnO₃) using mixed raw materials (La₂O₃, SrCO₃, and MnCO₃) was produced with a reactive plasma spray. Modeling for the particle vaporization process was carried out to investigate the particle behavior in a plasma flame. The reactively plasma sprayed deposits displayed large amounts of La_0.8Sr_0.2MnO₃ with relatively small amounts of SrO, MnO, and very little carbon. The degree of La_0.8Sr_0.2MnO₃ increased with decreasing feeding rate of the feedstock at 30 kW. A smooth surface and homogeneous pore distribution with pore size of less than 1 mm were obtained at low pressure (0.33 bar).     

La1-xKxMnO3的微波吸收特性

用溶胶-凝胶法制备La1-xKxMnO3粉晶,用X射线衍射仪和扫描电镜表征样品的晶体结构和微观形貌,用微波矢量网络分析仪测试了该样品在2~18 GHz微波频率范围的复介电常数和复磁导率,并计算损耗角正切及微波反射率,分析K掺杂量和样品厚度对体系微波吸收性能的影响及微波损耗机制。结果表明:晶体结构为钙钛矿型,颗粒形貌为不规则椭球状或短棒状;当样品厚度为2.40 mm、x=0.3时,吸收峰值为27.1 dB,10 dB以上有效吸收频带宽度达10.6 GHz。纳米La1-xKxMnO3兼具介电损耗和磁损耗,介电损耗相对较强。磁损耗因子和介电损耗因子随微波频率的变化相反,是基体中铁磁与反铁磁团簇在微波电磁场作用下相互转变引起。     

La-Ho-Fe合金的制备及其微波吸收特性研究

采用电弧熔炼及高能球磨工艺制备出LaxHo2-xFe17(x=0.0, 0.2, 0.4, 0.6, 0.8) 合金微粉,借助XRD、SEM、VSM和网络矢量分析仪等仪器分别研究La替换对合金微粉的结构、形貌、磁性能及其微波吸收性能的影响。结果表明, 随着La含量的增加,饱和磁化强度和平均颗粒大小都有所增加。LaxHo2-xFe17合金的最小反射峰频率向低频方向移动。其中La0.2Ho1.8Fe17合金具有最好的吸波效果,在最佳匹配厚度1.8 mm下,La0.2Ho1.8Fe17合金的最小反射损耗在8.72 GHz处达到-28.72 dB,反射损耗小于-10 dB的频带宽度达到2.32 GHz。当厚度在1.2-2.4 mm范围里,La0.2H1.8Fe17合金的反射损耗均小于-10 dB,这表明LaxHo2-xFe17是有前途的微波吸收材料,并具有良好的吸收特性。     

Crystal microstructure, infrared absorption, and microwave electromagnetic properties of （La1-xDyx）2/3Sr1/3MnO3

The manganite perovskite polycrystal samples of (La_1−x Dy _x )_2/3Sr_1/3MnO₃ (x = 0, 0.1, 0.2, 0.35, and 0.5) doped with Dy were prepared by solid state reaction in atmosphere to measure their X-ray diffraction (XRD) patterns, scanning electric microscope (SEM) images, infrared absorption spectra, and microwave electromagnetic properties. The displacement of the XRD peaks of the samples was found, and the 2ϑ increases from 0.05° to 0.5°. The grains of undoped La_2/3Sr_1/3MnO₃ not only have the greatest size, but also the most regular shape. The size of the grains decreases as the Dy doping content increases from 0 to 0.5. The infrared absorption spectra of all samples were measured at room temperature. An absorption peak corresponding to the stretching vibration mode of Mn-O bonds appears within the range of 591–629 cm⁻¹. The absorption peak shifts from a higher frequency to a lower one with the decrease of the average ionic radius of A-site. The frequency dependence of microwave-absorbing properties, imaginary components of the complex magnetic permeability μ″ and dielectric permeability ε″ for all samples was measured at room temperature from 8 to 13 GHz. The results show that the loss of microwave absorption can be attributed to both the magnetic and electric losses. The increase of Dy content not only enhances the microwave absorption but also causes the displacement of the absorption peaks.     

Wideband electromagnetic wave absorber using doped barium hexaferrite in Ku-band

Substituted barium hexaferrite BaMg_0.25Mn_0.25Co_0.5Ti_1.0Fe₁₀O₁₉ was prepared in powder configuration by solid state reaction. The ferrite powders were mixed with polyvinylcloride (PVC) plasticizer to fabricate a microwave absorbing composite. X-ray diffraction (XRD), scanning electron microscope (SEM), vibrating sample magnetometer (VSM), and vector network analyzer were employed to characterize phase identification coupled with size and morphology of powder and microwave absorption properties of synthesized composites. It was found that the maximum reflection loss of −40 dB was appeared at frequency range of 12-18 GHz. In the present work, new cation substitutions in iron sites in the crystal lattice of barium ferrite, which can easily tune the bandwidth of the reflection loss, were used. To the best of our knowledge, this is the first study which displays the wideband absorber by employing single layer hexaferrite backed on the surface of copper.     

Dy对Pr2Fe17合金微波吸收特性的影响

采用电弧熔炼及高能球磨工艺制备出 DyxPr2-xFe17 (x =0.0, 0.1, 0.2, 0.3, 0.4) 合金微粉,借助XRD、SEM、振动样品磁强计和网络矢量分析仪等仪器分别对合金微粉的结构、形貌、磁性能及其微波吸收性能进行了研究。研究发现, 随着Dy含量的增加,DyxPr2-xFe17微粉的饱和磁化强度降低。DyxPr2-xFe17合金的最小反射峰频率随Dy含量的增加往高频方向移动,最小反射损耗呈先增大后减小的变化趋势;其中Dy0.3Pr1.7Fe17合金具有最好的吸波效果,在最佳匹配厚度2.5 mm下,Dy0.3Pr1.7Fe17合金的最小反射损耗在5.04 GHz处达到-42.38 dB左右,反射损耗小于-10 dB的频带宽度达到了1.20 GHz。     

Synthesis and characterization of nanosized urchin-like α-Fe2O3 and Fe3O4: Microwave electromagnetic and absorbing properties

Urchin-like α-Fe₂O₃ and Fe₃O₄ nanostructures were prepared from the precursor urchin-like α-FeOOH under reducing atmosphere. The dependence of reduction temperature on their morphology, microstructure, and microwave electromagnetic and absorbing characteristics were systematically studied. It is found that the reduction temperature plays an important role in the microstructure and electromagnetic characteristics of the resulting products. In present study, the urchin-like α-Fe₂O₃ with dual absorption peaks can be formed at the relatively low temperature (e.g. 300 °C). Urchin-like Fe₃O₄ can be obtained just at 350-400 °C, which presents excellent microwave absorption property, with the minimum reflection loss of −29.96 dB and below −20 dB in 3.76-8.15 GHz corresponding to 3-4 mm thickness. The excellent microwave-absorption properties are a consequence of a proper electromagnetic matching and enhanced absorbing abilities resulting from the urchin-like shape and inverse spinel-type crystal structure.     

高性能雷达吸波涂层的制备及其损伤行为

以羰基铁粉为吸收剂、聚氨酯为胶黏剂,制备具有优异吸波性能的雷达吸波涂层,并基于矢量网络分析仪、电磁模拟软件Ansoft HFSS以及弓形框测试系统,对涂层电磁特性、损伤模型以及吸波性能进行研究。结果表明:雷达吸波涂层在垂直入射条件下具有优异的吸波性能,当涂层厚度为0.8 mm时,其反射损耗峰在7.2~12.8 GHz均达到?8 dB;在斜入射条件下也具有优异的吸波性能,当涂层厚度为0.8 mm、入射角为60°时,其反射损耗峰在5.5~18 GHz均达到?10 dB。相比于失效模式如雷达吸波涂层分层脱粘,损伤脱落对其吸波性能的影响更为明显。随着损伤脱落面积的增加,雷达吸波涂层的吸收强度（尤其是X波段）明显降低,且最小反射损耗峰往高频移动。通过对高性能雷达吸波涂层的脱落、分层等损伤行为的研究,为后续进行雷达吸波涂层维护与建立失效性评估标准具有极大的现实和军事意义。     

Effect of Critical Plasma Spray Parameters on Microstructure and Microwave Absorption Property of Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>/Cordierite Coatings

Ti₃SiC₂/cordierite coatings with different critical plasma spray parameters (CPSP) were fabricated via atmospheric plasma spraying method. The microstructure and phase constitution of the as-sprayed Ti₃SiC₂/cordierite coatings were characterized. The effects of CPSP conditions on the electromagnetic shielding, and dielectric and microwave absorption properties of coatings in the frequency of 8.2-12.4 GHz were also measured and investigated. The results showed that both real and imaginary part of the complex permittivity decrease with increasing CPSP values, which can be ascribed to the decomposition of some Ti₃SiC₂ into TiC. The calculated reflection loss of the as-sprayed Ti₃SiC₂/cordierite coatings with different CPSP conditions and thicknesses indicates that coatings with CPSP 0.3, 0.35, and 0.425 exhibit excellent microwave absorption property in the thickness of 1.5 mm. In order to broaden the bandwidth of the coatings, a double-layer coating system was designed. The calculated reflection loss results show that when the thickness of matching layer is 0.3 mm and the thickness of absorbing layer is 1.5 mm, the double-layer coating system shows a proper microwave absorption property with a minimum absorption value of ?17.37 dB at 9.67 GHz and a absorption bandwidth (RL less than ?5 dB) of 4.16 GHz in the investigated frequency.     

Synthesis and microwave absorbing properties of polyaniline/MnFe2O4 nanocomposite

Conductive polyaniline (PANi)-manganese ferrite (MnFe₂O₄) nanocomposites with core-shell structure were synthesized by in situ polymerization in the presence of dodecyl benzene sulfonic acid (DBSA) as the surfactant and dopant and ammonium persulfate (APS) as the oxidant. The structure and magnetic properties of manganese ferrite nanoparticles were measured by using powder X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. Its morphology, microstructure and DC conductivity of the nanocomposite were characterized by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and four-wire-technique, respectively. The microwave absorbing properties of the nanocomposite powders dispersing in resin acrylic coating with the coating thickness of 1_.4 mm were investigated by using vector network analyzers in the frequency range of 8-12 GHz. A minimum reflection loss of −15.3 dB was observed at 10.4 GHz.     

Infrared emissivity of Sr doped lanthanum manganites in coating form

The Sr doped lanthanum manganite coatings were prepared using La_0.8Sr_0.2MnO₃ particles and epoxy modified polyurethane as pigment and resin matrix, respectively. The structure, morphology, surface roughness and infrared normal emissivity (?_N) in the 3-5 and 8-14 μm wavebands of the samples were systematically investigated. With the increase of La_0.8Sr_0.2MnO₃ pigment, the ?_N of the coatings decreases and the ?_N values in the 8-14 μm waveband are higher than those in the 3-5 μm waveband. The surface roughness has no significant effect on the infrared emissivity of LSMO coatings. For 50% LSMO coating, the sample shows variable-emissivity property in the 8-14 μm waveband and the emissivity property remains unchanged before and after ultraviolet irradiation.     

Electromagnetic and microwave absorbing properties of W-type barium ferrite doped with Gd<Superscript>3+</Superscript>

W-type barium ferrites doped with Gd3+,Ba1-xGdx(Zn0.3Co0.7)2Fe16O27(x = 0,0.05,0.10,0.15,0.20),were prepared by a sol-gel method.The effects of Gd3+ substitution on their microstructure,electromagnetic properties and microwave absorptive behavior were analyzed.The XRD patterns showed the single phase of W-type barium ferrite when x ≤ 0.15.Microwave electromagnetic properties of samples were studied at the frequency range from 2 GHz to 18 GHz using a network analyzer(Agilent 8722ET).The complex permittivity ...     

钴-铁沉积碳化硅颗粒及其吸波性能

目的提高碳化硅微粒的微波吸收性能。方法利用改进的化学镀法,以硫酸钴和硫酸亚铁为主盐,次亚磷酸钠为还原剂,施镀温度为50℃,使用机械搅拌和超声分散相结合的方法,在预处理后的微米碳化硅颗粒表面沉积钴铁合金。通过X射线衍射仪(XRD)、X射线能谱仪(EDS)和扫描电子显微镜(SEM)分别对化学镀前后材料的结晶状态、组成成分和形貌特征进行了表征;利用矢量网络分析仪对化学镀前后材料在2~18 GHz频率范围内的电磁性能进行了测试,并通过计算得到了材料微波反射率损耗。结果钴铁合金呈微球状均匀沉积在碳化硅表面,有效地改善了碳化硅材料的电磁性能和微波吸收性能。碳化硅的介电常数虚部存在界面极化和缺陷极化两个弛豫峰(9.1、13.8 GHz),而沉积钴铁合金后,碳化硅材料Co-Fe/SiC增加了两个弛豫峰:介电弛豫峰(11.7 GHz)和磁弛豫峰(12.6 GHz)。正是由于Co-Fe合金对微波信号的介电弛豫和磁弛豫,有效提升了材料的吸波性能。当吸波层厚度为2.4 mm时,反射率在10 dB以上的吸收带宽达到3.8 GHz,20 dB带宽可以达到1.5 GHz。当吸波层厚度为2.3 mm时,频率为12.7 GHz时达到最大吸收峰值–43 dB。结论在碳化硅材料表面沉积钴铁合金是一种有效改进材料微波吸收性能的方法,且该材料是一种高效、宽频的微波吸收材料。     

Design of mesostructured γ-Fe2O3/carbon nanocomposites for electromagnetic wave absorption applications

We propose and demonstrate a scheme to enhance microwave absorption property through mesoporous structure with high regularity. The mesostructured nanocomposites, embedding γ-Fe₂O₃ within carbon matrix, exhibit a strong and broadband attenuation of microwave in the frequency range of 0.5-18 GHz, mainly due to the better impedance matching. C-2Fe-900 exhibits strong absorption characteristics with an absorption peak of −32.0 dB at 6.4 GHz. The absorption peak intensity and position can be adjusted by changing the matching thickness of the coating. Reflection loss below −10 dB (i.e., absorption above 90%) is obtained in the frequency range of 1.9-10.7 GHz.     

玻璃包覆FeSiBNbCu非晶丝的微波吸收性能(英文)

制备以石蜡为基体并具有玻璃包覆Fe73.5Si13.5B9Nb3Cu1非晶丝不同填充比的同轴介电样品,在相对较高的微波吸收频段(2~18 GHz)下研究短丝填充比(质量分数3%~9%)和样品厚度(1~7 mm)对同轴介电样品的微波吸收性能的影响规律。采用X射线衍射谱(XRD)、差示扫描量热分析(DSC)、扫描电子显微分析(SEM)和矢量网格分析仪(SNA)表征材料的微结构并评价其吸波性能。结果表明,不同填充比的同轴介电样品的复磁导率和复介电常数存在重要的频率范围(6~18 GHz)。模拟结果显示,具有3 mm厚度和7%填充比的样品具有较好的微波吸收性能,其反射率在14 GHz时达到峰值-34 dB。这对于开发具有更宽微波吸收范围应用的微丝介电材料是十分有益的。