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。     

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%。     

W型铁氧体BaCoZnRe0.1Fe15.9O27的制备及吸波性能研究

为研究稀土掺杂W型铁氧体材料的吸波性能,实验用溶胶-凝胶法制备了W型铁氧体BaCoZnRe0.1Fe15.9O27(Re=Ce、La、Nd),研究了Re3+掺杂对W型铁氧体性能的影响.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、振动样品磁强计(VSM)和矢量网络分析仪等分析其物相组成、形貌、磁性能和微波吸收性能.结果表明:制得的Re3+掺杂W型铁氧体为六角片状结构,呈顺磁性;当样品BaCoZnFe16O27中掺杂Re3+离子后,样品的晶粒尺寸变小,ε’减小,ε″增加,磁性能增强;BaCoZnNd0.1Fe15.9O27样品的饱和磁化强度(M s)值最大,其tanδ在10.1 GHz处达到最大值0.58,吸波性能在2~13 GHz内最好.     

(1-x)Pb(Fe2/3W1/3)O3-xPb(Mg1/2W1/2)O3多铁性材料的有序结构及磁性能

以无机盐为前驱体,利用溶胶-凝胶法固溶合成了(1-x)Pb(Fe2/3W1/3)O3-xPb(Mg1/2W1/2)O3多铁性固溶体.XRD分析表明,在0≤x≤1.0的掺杂范围内,700℃煅烧所得产物都具有钙钛矿结构;x=0时得到的纯Pb(Fe2/3W1/3)O3为长程无序结构,x=1.0时可获得完全有序的纯Pb(Mg1/2W1/2)O3相,其单胞为Pb(Fe2/3W1/3)O3单胞的2倍;当0相似文献   

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.     

溶胶-凝胶法制备锌掺杂Sr_3Co_2Fe_(24)O_(41) Z型铁氧体及其性能

利用柠檬酸溶胶-凝胶法合成了锌掺杂Sr_3(Zn_xCo_(1-x))_2Fe_(24)O_(41),(x=0～0.8)的Z型铁氧体.测试其结构、磁性能、电磁性能与吸波特性.实验结果表明,适量掺杂Zn~(2+)有利于磁性能及吸波性能的改善,在x=0.2时比饱和磁化强度最大,可达51.36 A·m~2·kg~(-1);吸波性能优良,最大吸收量为35.12dB;合成最佳温度为1200℃烧结2小时.     

Tb掺杂对BiFeO3粉晶结构和磁性的影响

采用溶胶-凝胶法制备了Tb掺杂的BiFeO3粉晶,其掺杂浓度为0≤x≤0.2,分别用X射线衍射仪、Ra-man散射仪和综合物性测量系统对Bi1-xTbxFeO3粉晶样品的结构、Raman活性振动模式和磁性进行了测量和分析。实验结果表明:当Tb掺杂量x在0.10～0.125时,母体BiFeO3的结构由菱形R3c相变为正交Pnma相,同时伴随着铁电-顺电相的变化。另外,随着掺杂浓度的增大,Bi1-xTbxFeO3的磁性逐渐增强,并且在铁电-顺电相相变边界处(x=0.10),剩余磁化强度Mr达到最大值0.223emu/g,约为纯相BiFeO3的8倍。随着Tb掺杂量进一步增大(x≥0.125),样品的剩余磁化强度开始逐渐减小,其原因是在正交相的样品中磁矩逐渐形成了很好的反平行排列。     

锆镍掺杂量及烧结温度对M型钡铁氧体吸波性能的影响

利用溶胶-凝胶法,在1 200～1 400℃烧结制备了Zr~(4+)-Ni~(2+)共掺杂钡铁氧体Ba(ZrNi)_xFe_(12-2x)O_(19)(x=0.6～0.9),研究了掺杂量及烧结温度对M型钡铁氧体晶相结构、微观形貌、电磁性能和吸波性能的影响。结果表明随着锆镍掺杂量和烧结温度的增加,样品的晶体结构和化学成分不发生变化,都形成了片状的单相锆镍掺杂钡铁氧体。晶粒尺寸随掺杂量增加几乎不变化而随烧结温度提高逐渐从100～300 nm增加到1～2 mm。所有样品中均可观察到多自然共振峰,自然共振强度随掺杂量的增加整体呈下降的趋势,而介电常数随烧结温度升高会显著增加。最终,1 400℃烧结的掺杂量x=0.6的样品可获得最优异的吸波性能,在匹配厚度3.25 mm下,最小反射损耗为-16.4dB,同时有效吸波频宽可达5.22 GHz(8.62～13.84 GHz)。     

Cr掺杂Ba0.5Sr0.5Co0.8Fe0.1Cr0.1O3-δ钙钛矿型膜的透氧性能研究

采用固相反应法合成了钙钛矿型Ba0.5Sr0.5Co0.8Fe0.2-xCrxO3-δ(x=0.00,0.10)透氧膜粉体。利用XRD和SEM研究了Ba0.5Sr0.5Co0.8Fe0.2-xCrxO3-δ(x=0.00,0.10)的晶体结构和烧结性能,考察了在700~850℃范围内Ba0.5Sr0.5Co0.8Fe0.2-xCrxO3-δ(x=0.00,0.10)膜片的氧渗透性能。结果表明,它们均显示出优良的透氧性能,850℃时的透氧量分别为1.05mL/(min.cm2)、0.85mL/(min.cm2)。透氧稳定性的研究表明,Cr掺杂Ba0.5Sr0.5-Co0.8Fe0.1Cr0.1O3-δ在800℃时显示出较高的稳定性,证实用Cr离子部分取代Ba0.5Sr0.5Co0.8Fe0.2O3-δ的Fe离子能明显提高钙钛矿的结构稳定性。     

多铁性材料Bi1-xBaxFeO3的微波吸收性能

用溶胶-凝胶法制备了Bi1-xBaxFeO3(x=0.0,0.15,0.25,0.35,0.4),用X射线衍射(XRD)和扫描电镜(SEM)表征了样品的晶体结构、微观形貌,用综合物性测试系统(PPMS)测试了样品的室温磁滞回线,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、复磁导率并计算了电磁损耗因子和微波反射率,分析了材料的微波吸收性能和电磁损耗机制。结果表明:Bi1-xBaxFeO3粉晶呈球状,晶体结构为钙钛矿型,呈较弱的铁磁性;当x=0.35、厚度d=2.7mm时,在频率f=10.64GHz位置的吸收峰值为30.43dB,10dB带宽为2.4GHz,微波吸收以介电损耗为主兼具一定的磁损耗。     

用精铁矿粉制备BaZnCoTi-W型微波吸收铁氧体材料

利用称重、磁性探测和XRD图谱相结合的方式,分析了精铁矿粉的氧化相变过程,发现在750℃时,精铁矿粉被氧化生成α-Fe2O3;采用氧化工艺,直接用精铁矿粉和BaCO3一次烧结制备W型钡铁氧体BaZn1-aMnaCo1+0.5xTi0.5xFe16-XO27,分别研究了Co2+Ti 4+含量(x值)和涂层厚度对磁性能的影响,结果表明:当厚度为2.1mm及x=1.25时,样品在x全波段内(8～12GHZ)吸收衰减大于10dB,吸收峰达到31dB。     

基于多朗德因子和低磁晶各向异性场的钒镍共掺杂钡铁氧体毫米吸波材料

采用溶胶-凝胶法制备了V5+掺杂和V5+-Ni2+共掺钡铁氧体.采用SEM、XRD、XPS等手段对粉末的微观结构进行了表征,并利用矢量网络分析仪对电磁性能进行了测试.与V5+取代体系相比,V5+-Ni2+共掺杂钡铁氧体可减小其磁晶各向异性场和引入三个不同的Landé因子(g),具有更好的吸波性能.当V5+-Ni2+共掺...     

A study on the behavior of laminated electromagnetic wave absorber

Since ferrites are electromagnetic wave absorbing materials of composition-dependent resonance type, useful frequency ranges are typically narrow. In the present study, laminated electromagnetic wave absorbers composed of ferrite-ferrite or ferrite-dielectric layers were constructed to improve electromagnetic wave absorbing properties. When ferrites of different composition and thickness were layered, center frequency of the laminated ferrite could be changed over a range of values lying between the center frequencies of each ferrite. Compared with monolithic ferrites, ferrite-dielectric laminates exhibited broader frequency ranges with 20 dB or more attenuation     

La掺杂纳米晶Ni-Zn铁氧体的制备及电磁性能

采用高分子凝胶法制备了Ni0.5Zn0.5LaxFe2-xO4（x=0,0.02,0.05和0.08）纳米晶铁氧体.采用X射线衍射仪（XRD）、透射电镜（TEM）和HP8510网络分析仪分别对其结构、形貌和电磁性能进行了研究.结果表明,当x=0,0.02和0.05时,所得粉体为纯立方晶系尖晶石结构.Ni0.5Zn0.5Fe2O4粉体平均粒径为70nm.随着La离子掺杂量的增加,红外光谱中550cm-1处吸收峰向高波数移动,420cm-1处吸收峰向低波数移动.La离子的掺杂对Ni-Zn铁氧体的电磁性能有一定的影响.在X波段,与Ni0.5Zn0.5Fe2O4铁氧体相比,掺杂La的Ni-Zn铁氧体的tanδm值降低,tanδε值升高.Ni0.5Zn0.5La0.02Fe1.98O4铁氧体的tanδε平均值为0.616.     

平面六角晶系铁氧体混合材料涂层的优良吸波特性*

对W型和Y型复合组分平面六角晶系铁氧体的制备及两者混合材料涂层的吸波特性进行了研究,并对其复相对介电系数和复相对磁导率以及吸收衰减量随微波信号频率、掺杂Co^2 、Ti^4 含量、涂层厚度的变化进行了测试和分析,发现当表示含杂量的x=0.75,y=0.4时,铁氧体的吸波性能最佳,其匹配厚度为1.64mm,吸收衰减量最大可达37.5dB。     

Structural and Magnetic Studies of Rare-Earth Substituted Nickel Ferrites

Polycrystalline ferrites NiFe₂O₄ and NiFe_1.99R_0.01O₄ (R=Sm, Gd, Eu, and La) samples were prepared by usual ceramic method. The structural and the magnetic properties of the samples were characterized by X-ray powder diffraction (XRD), Mössbauer Effect (ME) spectroscopy, and vibrating sample magnetometer (VSM). Indexed XRD patterns confirm the formation of pure cubic spinel phase. The lattice parameters (a) of the rare earth (R) doped samples were smaller than that of the pure Ni-ferrite. Mössbauer effect spectroscopy was used to study the distribution of cations in tetrahedral (A) and octahedral [B] sites of the spinel. The hysteresis loops indicated that the saturation magnetization and coercivity increased with R-substitution and appeared to be greatly affected by the nature of R ions. The obtained results are interpreted based on the rearrangement of cations between the A-site and B-site.     

Exchange coupling controlled ferrite with dual magnetic resonance and broad frequency bandwidth in microwave absorption

Ti-doped barium ferrite powders BaFe_12−xTi_xO₁₉ (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were synthesized by the sol–gel method. The phase structure and morphology were analyzed by x-ray diffraction (XRD) and scanning electron microscopy, respectively. The powders were also studied for their magnetic properties and microwave absorption. Results show that the Ti-doped barium ferrites (BFTO) exist in single phase and exhibit hexagonal plate-like structure. The anisotropy field H_a of the BFTO decreases almost linearly with the increase in Ti concentration, which leads to a shift of the natural resonance peak toward low frequency. Two natural resonance peaks appear, which can be assigned to the double values of the Landé factor g that are found to be ∼2.0 and ∼2.3 in the system and can be essentially attributed to the existence of Fe³⁺ ions and the exchange coupling effect between Fe³⁺ and Fe²⁺ ions, respectively. Such a dual resonance effect contributes a broad magnetic loss peak and thus a high attenuation constant, and leads to a dual reflection loss (RL) peak over the frequency range between 26.5 and 40 GHz. The high attenuation constants are between 350 and 500 at peak position. The optimal RL reaches around −45 dB and the practicable frequency bandwidth is beyond 11 GHz. This suggests that the BFTO powders could be used as microwave absorbing materials with extraordinary properties.     

High entropy rare earth hexaborides/tetraborides (HE REB6/HE REB4)composite powders with enhanced electromagnetic wave absorption performance

The increasing electromagnetic hazards including electromagnetic interference and electro-magnetic pollution,which were stemmed from massive usage of electromagnetic technology,have triggered widespread concerns.To cope with this challenge,electromagnetic wave absorbing materials with high performance are greatly needed.Composite construction has been widely applied in electromagnetic (EM) wave absorbing materials to achieve high per-mittivity,high permeability and impedance matching.However,high-temperature stability,oxidation and corrosion resistance are still unignorable issues.Herein,high entropy hexa-borides/tetraborides (HE REB6/HE REB4) composites with synergistic dielectric and magnetic losses were designed and successfully synthesized through a one-step boron carbide reduction method.The five as-prepared (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)B6/(Y0.2Nd0.2Sm0.2Eu0.2Er0.2)B4,(Y0.2Nd0.2Sm0.2 Er0.2Yb0.2)B6/ (Y0.2Nd0.2Sm0.2Er0.2Yb0.2)B4,(Y0.2Nd0.2Eu0.2Er0.2Yb0.2)B6/ (Y0.2Nd0.2Eu0.2Er0.2Yb0.2)B4,(Nd0.2 Sm0.2 Eu0.2 Er0.2Yb0.2)B6/ (Nd0.2 Sm0.2 Eu0.2 Er0.2Yb0.2)B4 and (Y0.2 Sm0.2 Eu0.2 Er0.2Yb0.2)B6/(Y0.2 Sm0.2 Eu0.2 Er0.2Yb0.2)B4 contain two phases of HE REB6 and HE REB4.Among them (Y0.2 Nd0.2Sm0.2 Eu0.2 Er0.2)B6/ (Y0.2Nd0.2Sm0.2Eu0.2Er0.2)B4 (HE REB6/ HE REB4-1) and (Y0.2Nd0.2Sm0.2Er0.2Yb0.2)B6/(Y0.2Nd0.2Sm0.2Er0.2Yb0.2)B4 (HE REB6/ HE REB4-2) exhibit excellent EM wave absorption proper-ties.The optimal minimum reflection loss (RLmin) and effective absorption bandwidth (EAB) of HE REB6/HE REB4-1 and HE REB6/HE REB4-2 are-53.3 dB (at 1.7 mm),4.2 GHz (at 1.5 mm) and-43.5 dB(1.3 mm),4.2 GHz (1.5 mm),respectively.The combination of conducting HE REB4 with magnetism into HE REB6 as a second phase enhances dielectric and magnetic losses,which lead to enhanced EM wave absorption performance.Considering superior high-temperature stability,oxidation and corrosion resistance of HE REB6 and HE REB4,HE REB6/HE REB4 composite ceramics are promising as a new type of high-performance EM wave absorbing materials.