W型Ba0．8La0．2Co2Fe16O27微波吸收材料的制备与表征

采用柠檬酸溶胶凝胶法制备了稀土W型六角铁氧体Ba0.8La0.2Co2Fe16O27粉晶,用DSC-TGA、FT-IR、XRD、SEM分析了样品的形成过程、微观形貌、粒径和晶体结构,根据微波矢量网络分析仪测试的样品在2～18GHz微波频率范围的电磁参数计算了电磁损耗角正切及微波反射率.研究结果表明, 煅烧2h能得到单一的W型相Ba0.8La0.2Co2Fe16O27 ;晶粒为六角块状结构,大小均为200nm左右;Ba0.8La0.2Co2Fe16O27样品厚度为1.9mm时,12GHz位置处吸收峰为16.2dB,10dB频宽为4.0GHz;微波吸收主要由磁损耗引起.     

纳米镍铜铁氧体粒子的制备与微波吸收特性研究

采用溶胶 凝胶法制备了纳米镍铜铁氧体粒状材料,并对其吸波性能进行研究。实验结果表明,镍铜铁氧体有很好的微波吸收特性,在微波波段有两个吸收峰,较大的吸收峰在 9. 834GHz 处,其值为13.3dB,半峰宽度为3.612GHz。然后,把不同微量稀土铈掺杂到镍铜铁氧体当中,发现适量的稀土铈能提高镍铜铁氧体的吸波性能。较大的吸收峰向高频移动到10.049GHz,其吸收值提高到 21.906dB,半峰宽度展宽为 4.322GHz。镍铜铁氧体是一种有应用价值的新型微波吸收材料。     

化学共沉淀法制备的纳米Ni0.5Zn0.5CexFe2-xO4铁氧体微波吸收特性研究

采用化学共沉淀法制备了纳米Ni0.5Zn0.5CexFe2-xO4(x=0,0.005,0.01,0.015)铁氧体吸波材料,用AV3618型微波矢量网络分析仪测试了样品在8.2～12.5GHz范围内的微波吸收特性,实验结果表明:稀土元素铈的含量影响材料的吸波性能,当x=0.01时, 纳米Ni0.5Zn0.5CexFe2-xO4铁氧体的吸波性能最佳.对于Ni0.5Zn0.5Ce0.01Fe1.99O4铁氧体吸波材料,当涂层厚度为1mm时,在测试频段内有三个吸收峰,在8.8GHz处,其最大吸收衰减量为15.4dB,10 dB以上带宽达3.8GHz,适量掺杂稀土元素铈是提高镍锌铁氧体吸波材料性能的一种有效途径.     

Sr0.7La0.15Ce0.15Fe11.7Zn0.3O19/PAn复合材料的制备及微波吸收性能

用溶胶-凝胶法制备了La、Ce、Zn掺杂锶铁氧体Sr0.7La0.15Ce0.15Fe11.7Zn0.3O19纳米粉晶,再通过原位聚合反应法制备了掺杂锶铁氧体/聚苯胺(PAn)复合材料.用XRD、SEM、FTIR对样品进行表征,用微波网络分析仪测量了样品在2～12.4GHz频率范围的微波反射率(R).研究结果表明,聚苯胺包覆于掺杂锶铁氧体粒子表面,Sr0.7La0.15Ce0.15Fe11.7Zn0.3O19/PAn微波吸收性能优良,具有磁损耗和电损耗协同作用.复合样品厚度为3mm时,10GHz频率位置吸收峰值为-28dB,10>dB吸收带宽为4.7GHz.从R随频率变化的曲线趋势看,最佳匹配厚度为2.6mm,吸收峰值接近-40dB,峰值频率高于12.4GHz,>10dB吸收带宽预计达到5.5GHz.     

(1-x)BaFe12O19/xBaTiO3复合吸波材料的制备及微波吸收性能

采用溶胶-凝胶法制备了(1-x) BaFe12O19/xBaTiO3复合吸波材料(x=0、0.1、0.3、0.5、0.7、0.9、1).研究了钛酸钡含量对复合样品晶体结构、微观形貌以及微波性能的影响.结果表明,于900℃煅烧的样品形成了BaFe12O19相和BaTiO3相共存的BaFe12O19/BaTiO3复合体系;当钛酸钡含量在0.3～0.7时,复合样品的介电损耗和磁损耗显著增强,提高了微波吸收性能,拓宽了有效吸收频带;当厚度为3mm时,x=0.5的复合样品在频率为13GHz处的最强吸收峰为14.8dB,x=0.7的复合样品的有效吸收频宽可达3.4GHz.     

W型铁氧体Ba（MnCu）xCo2-2xFe16O27的微波吸收性能

采用溶胶-凝胶法制备了(MnCu)组合掺杂W型钡钴铁氧体Ba(MnCu)xCo2-2xFe16O27(x=0.1、0.2、0.3、0.4、0.5)样品。用XRD和SEM对样品的晶体结构、表面形貌、粒径进行了表征,用微波矢量网络分析仪测试了该样品在2~18GHz微波频率范围的电磁参数,根据测量数据计算电磁损耗角正切及得出微波反射率与频率的关系,探讨了该材料的微波吸收性能与电磁损耗机理。研究结果表明,Ba(MnCu)xCo2-2xFe16O27晶粉呈微米级六角片状形貌,煅烧温度1235℃以上的晶体结构为W型,是一种宽频带强损耗微波吸收材料。当x=0.3时,厚度为2.3mm的样品在频率为10GHz处的吸收峰为24dB,10dB以上频带宽度达8.8GHz。样品的微波吸收主要来自畴壁共振、磁化弛豫和自然共振引起的磁损耗,介电损耗较弱。     

稀土元素对W型钡铁氧体微波吸收特性的作用

采用化学共沉淀法制备W型钡铁氧体,研究稀土元素Dy、Nd、Pr掺杂对铁氧体微波特性的作用.发现:稀土元素的掺入能有效调整铁氧体的微波电磁参数,使自然共振频率向高频移动,并明显提高试样的高频弛豫特征,同时减小复介电常数,以利于阻抗匹配.在一定范围内增大Dy的掺杂量x,有利于进一步获得低介电损耗和高磁损耗,用数值计算模拟方法得到x=0.05时匹配厚度下铁氧体在2～18GHz范围的反射率曲线:吸收峰值达-52.34dB,吸收率小于-10dB的带宽7.9GHz,结果表明稀土Dy掺杂有利于制备轻、薄铁氧体吸波材料.     

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.     

多铁性材料BiFe_(1-x)Co_xO_3的微波吸收特性研究

用溶胶-凝胶法制备BiFe1-x Cox O3样品,用X射线衍射仪、扫描电镜、能谱分析对样品的结构、微观形貌、元素组成进行了表征,用微波矢量网络分析仪测试了样品在2～18GHz微波频率范围的复介电常数、复磁导率,并计算了损耗角正切及微波反射率。结果表明,当掺杂量x=0、x=0.1、x=0.2,煅烧温度800℃时,产物的主相为钙钛矿型BiFeO3,同时还有杂相Bi25FeO40,颗粒形貌为尺寸约1.5μm的立方形;Co的掺入有利于提高体系的微波吸收性能。当样品厚度为1.8mm,x=0.2时,吸收峰值为-26.5dB,带宽为2.08GHz,在高频段有良好的微波吸收,材料兼具介电损耗和磁损耗但介电损耗相对较强。     

Mn在BaTiO3中的固溶及其对BaTiO3结构影响的研究

运用XRD、SEM、HRTEM研究了Mn2O3掺杂对钛酸钡陶瓷结构的影响.随着烧结温度上升,发现Mn2O3掺杂钛酸钡样品的晶格常数在c轴方向增大.在烧结温度相同的情况下,Mn2O3掺杂能够抑制钛酸钡晶粒的生长,Mn3 在烧结的过程中逐渐的固溶进入钛酸钡晶格.从结构角度出发,提出了Mn固溶进入晶格后,在其周边微区可能产生压应力,这是样品在还原气氛下烧结仍保持高电阻现象的原因之一.     

Dy1-xSrxFeO3的制备及其电磁吸收性能

采用传统固相法,制备了Dy1-xSrxFeO3(x=0、0.1、0.2、0.3、0.4)粉体,研究了其微波电磁性能。利用X射线衍射技术研究了其结构和相组成。利用扫描电镜观察粉体颗粒微观形貌。利用网络分析仪测试了其2～18GHz的电磁参数,并通过软件对其微波吸收性能进行了模拟,利用紫外-可见-红外分光光度计测量了其在930～1250nm波长区间的反射率。结果表明粉体为钙钛矿结构;当x=0.3,涂层厚度d=2.8mm时,在11GHz处吸收出现峰值,约为-20dB,2～18GHz范围内吸收>-10dB的频宽约为2.9GHz;当x=0.3时,粉末压片在950～1200nm波长区间的红外吸收性能最好,其反射率约为0.05%。     

The microwave absorbing properties of La<Subscript>0.8</Subscript>K<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript> synthesized by sol–gel method

In this paper, La_0.8K_0.2MnO₃ powder was synthesized by sol–gel method. The phase structure, morphology of the composite have been characterized by X-ray diffraction, field emission scanning electron microscope. Testing of the microwave absorption was carried out by using the network analyzer Agilent HP-8722ES at room temperature. The results show that the La_0.8K_0.2MnO₃ powder has excellent absorbing property. The maximum reflection loss is ?33.51 dB at about 12.22 GHz with a thickness of only 1.25 mm. Moreover, the bandwidth with the reflection loss above 10 dB reaches about 2.1 GHz.     

静电纺制备Fe3O4/PEK-C纳米复合膜及其吸波性能

静电纺丝技术是一种新颖、高效且简单的制备连续纳米纤维的方法,纳米复合纤维膜的优异特点赋予了纳米吸波剂新的吸波通道。本文采用静电纺丝工艺制备Fe3O4/PEK-C纳米复合纤维膜,利用SEM和TGA表征纳米复合纤维膜的微观形貌和热稳定性,用矢量网络分析仪测试样品在8.2~12.4 GHz的电磁参数与吸波性能。结果表明,Fe3O4/PEK-C纳米复合纤维膜呈现出超细纤维彼此交织构成的立体网络结构,其热稳定性、复介电常数和复磁导率均随着Fe3O4含量的增加而增加,介电损耗和磁损耗得到加强。当纳米复合纤维膜的厚度为1.8 mm时,其反射损耗在整个测试波段均处于-5 dB以下,-10 dB以下有效吸收频宽为2 GHz,频率在8.6 GHz处吸收强度达到最大值-15.4 dB。预期可作为隐身复合材料的吸波功能层。     

Synthesis and microwave absorption enhancement of Fe-doped NiO@SiO2@graphene nanocomposites

Fe-doped NiO@SiO₂@graphene nanocomposites have been successfully fabricated for the first time, in which Fe-doped NiO nanoparticles are about 3 nm in diameter. In order to measure their electromagnetic properties, Fe-doped NiO@SiO₂@graphene (25 wt%) wax composites were then prepared. The experimental results show that Fe-doped NiO@SiO₂@graphene nanocomposites exhibit significantly enhanced microwave absorption performance in terms of both the maximum reflection loss value and the absorption bandwidth in comparison with NiO@SiO₂@graphene. The maximum reflection loss of Fe-doped NiO@SiO₂@graphene nanocomposites can reach −51.2 dB at 8.6 GHz with a thickness of 4 mm, and the absorption bandwidth with the reflection loss below −10 dB is 4 GHz (from 7 to 11 GHz). Therefore, this kind of nanocomposites may have the potential as high-efficient absorbers for microwave absorption applications.     

Electromagnetic wave absorption performance of Ti2O3 and vacancy enhancement effective bandwidth

The microwave absorption properties of Ti2O3 were systematically investigated.Experimental results indicate that Ti2O3 has microwave absorption performance with a minimum reflection loss value of-37.6 dB at 18.6 GHz and an effective absorption bandwidth(RL＜-10 dB)of 2 GHz.Further,vacancy defects were introduced into Ti2O3 by carbothermal reduction.Interestingly,the effective absorption bandwidth of Ti2O3 with vacancy defects reach 3.2 GHz.First-principles calculations provide evidence that vacancy defects result in the changes of electric dipole state,leading to a wider effective absorption bandwidth.These results have significance in understanding the origin of electromagnetic phenomena and developing electromagnetic wave absorption materials.     

Sol–gel synthesis,characterization and microwave absorbing properties of nano sized spherical particles of La0.8Sr0.2Mn0.8Fe0.2O3

LSMFO (La_0.8Sr_0.2Mn_0.8Fe_0.2O₃) nano sized powders were synthesized by modified EDTA assisted sol–gel synthesis using EDTA:metal ion = 0.5. Another new synthesis method, sol–gel self combustion using PVA, was also devised for the synthesis of LSMFO and the effects of the PVA mole ratio was investigated. The characterization techniques, XRD, FE-SEM, TG/DTA and ICP, confirmed the formation of the pure phase LSMFO by both the methods. The material attained spherical morphology instead of previously reported rod like structure. Sizes of synthesized powders vary from 14.5 nm to 23 nm. TG/DTA results suggest that LSMFO can be synthesized by the self combustion at temperatures as low as 200 °C. Synthesized LSMFO has excellent microwave absorbing properties in the range of 0.05–18 GHz and appreciable effective bandwidth, 2 GHz, with microwave absorption in excess of 10 dB and peak reflection loss of 25 dB which suggests that the materials can be used as effective microwave absorbers.     

Enhanced electromagnetic wave absorption properties of polyaniline-coated Fe3O4/reduced graphene oxide nanocomposites

Fe₃O₄-reduced graphene oxide-polyaniline (Fe₃O₄–RGO–PANI) ternary electromagnetic wave absorbing materials were prepared by in situ polymerization of aniline monomer on the surface of Fe₃O₄–RGO nanocomposites. The morphology, structure and other physical properties of the nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, vibration sample magnetism, etc. The electromagnetic wave absorbing properties of composite materials were measured by using a vector network analyzer. The PANI–Fe₃O₄–RGO nanocomposites demonstrated that the maximum reflection loss was ?36.5 dB at 7.4 GHz with a thickness of 4.5 mm and the absorption bandwidth with the reflection loss below ?10 dB was up to 12.0 GHz with a thickness in the range of 2.5–5.0 mm, suggesting that the microwave absorption properties and the absorption bandwidth were greatly enhanced by coating with polyaniline (PANI). The strong absorption characteristics of PANI–Fe₃O₄–RGO ternary composites indicated their potential application as the electromagnetic wave absorbing material.     

Microwave absorption characteristics of CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript> perovskite/carbon nanotube composites

The CH₃NH₃PbI₃ (MAPbI₃) and CH₃NH₃PbI₃/carbon nanotube (MC) composite have been successfully synthesized by a facile in situ solution method, which are investigated as the microwave absorption materials. For the MAPbI₃ particles, the minimum reflection loss is only ?4.9 dB around 16.4 GHz due to the poor relative complex permittivity. Then, the relative complex permittivity of MC composites could be adjusted by changing the mass fraction of CNTs in composite, which is a vital role for the dielectric loss. The reflection loss of MC-5 composite (MAPbI₃/CNT, 5:1 wt%) can be improved to ?35.7 dB with thickness of 1.3 mm at 13.1 GHz. When the thickness is <3.0 mm, the microwave absorption bandwidth of MC-5 is 11.8 GHz (5.0–16.8 GHz) under the reflection loss lower than ?20 dB. The quarter-wavelength (λ/4) matching model is used to discuss the microwave absorption mechanism of MC composites. These results indicate that MC-5 composite could be used as the microwave absorption materials with strong reflection loss, lightweight and broad bandwidth.     

Regulating microwave absorption and energy bandgap using cauliflower-like polyaniline coated on La0.8Sr0.2FeO3 nanoparticles

In this research, La_0.8Sr_0.2FeO₃/cauliflower-like polyaniline (PANi) nanocomposite was architected based on a novel complementary method using dodecylbenzenesulfonic acid as a doping agent. The prepared nanocomposite was characterized using Fourier transform infrared, X-ray powder diffraction, field emission scanning electron microscopy, vibrating sample magnetometer diffuse reflection spectroscopy, and vector network analyzer analyses. All of the used analyses attested that the pure structure of materials has been synthesized. Polarizability, energy bandgap, magnetic property, and microwave absorbing features were tailored by loading the various mass fraction of PANi. Exclusive interactions between the nanoparticles with alkaline property and aniline monomers along the experimental route led to the preparation of nanocomposite with unique morphology. Inserting PANi augmented softness and isotropic magnetic property of the prepared nanocomposite, desirable for microwave absorption. Moreover, polyacrylonitrile (PAN) was applied as a novel microwave absorbing matrix. The maximum reflection loss (RL) of La_0.8Sr_0.2FeO₃/PANi_10%/PAN was ??69.24 dB at 12.62 GHz with an efficient bandwidth of 6.47 GHz (RL?<???10 dB) meanwhile the efficient bandwidth was enhanced to 6.97 GHz (RL?<???10 dB) for La_0.8Sr_0.2FeO₃/PANi_30%/PAN nanocomposite.