微波锂系铁氧体的磁性能研究

本文用正交试验设计方法研究了微波锂系铁氧体的微观结构参数(气孔率和平均晶粒尺寸)和微波磁性能(饱和磁化强度、共振线宽和介电损耗)随成分、工艺的变化规律,获得了可应用在低功率器件中的6366A/m(80_(?))的铁磁共振线宽铁氧体。首先,根据极差对不同成分、工艺对各参数和性能的影响进行了分析,表明Mg和Ti(1∶1)的取代量对多晶锂铁氧体材料的气孔率、饱和磁化强度和共振线宽的影响最显著,而Ca和V(2∶1)的取代量和烧结温度则分别对平均晶粒尺寸和介电损耗的影响最显著。同时,也对各因素的影响机理作了相应的探讨。最后,本文对多晶锂系铁氧体的成分-组织-性能间的联系进行了线性回归分析,结果表明气孔率和平均晶粒尺寸在很大程度上决定着多晶系铁氧体的共振线宽,并且前者的作用比后者的作用要大。     

Bi2O3掺量对Li0.45Ni0.2Ti0.1Fe2.25O4铁氧体显微结构及磁性能的影响

采用氧化物法陶瓷工艺,在缺铁配方的基础上,制备不同Bi2O3掺量的Li0.45Ni0.2Ti0.1Fe2.25-δO4(δ=0.06)铁氧体样品。结果表明,添加Bi2O3没有在锂铁氧体中形成杂相,烧结后陶瓷样品物相组成单一,结晶状况良好;适量的Bi2O3能有效改善材料微观形貌,促进锂铁氧体的烧结致密化,有助于提高材料的饱和磁化强度4πMs和剩磁比R,降低矫顽力Hc。Bi2O3掺量为1.5%(质量分数)的样品具有较好的综合性能,表观密度d为4.72g/cm3,饱和磁化强度4πMs为2.3T,剩磁比R为0.853,矫顽力Hc为2.3×102 A/m。     

镨掺杂钡铁氧体-聚吡咯复合膜的制备和性能

分别用溶胶-凝胶法和原位氧化聚合法制备了镨掺杂钡铁氧体/聚吡咯复合膜,借助X射线衍射仪(XRD)、红外光谱(FTIR)、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手段表征了复合膜的结构和形貌,研究了样品的磁性能和吸波性能.结果表明,复合膜的饱和磁化强度Ms和剩余磁化强度Mr均比钡铁氧体单膜的低...     

Bi2O3对烧结LiZn铁氧体性能的影响

采用氧化物陶瓷工艺制备了掺Bi2O3的Li0.4Zn0.2Fe24O4铁氧体．用XRD、SEM、密度测试和磁性能表征，研究了Bi2O3对LiZn铁氧体性能的影响．结果表明：Bi2O3能有效抑制烧结过程中的锂挥发，促进固相反应，降低烧结温度，但过多的Bi2O3会阻止晶粒生长；适量掺杂Bi2O3可以提高LiZn铁氧体的饱和磁感应强度和矩形比，降低铁氧体的矫顽力．     

Bi_2O_3和Bi(NO_3)_3掺杂对锂锌铁氧体微观结构和微波吸收性能的影响

采用溶胶凝胶法与后期煅烧相结合,制备了纯锂锌铁氧体及掺杂氧化铋和硝酸铋的铁氧体.扫描电镜和X射线衍射研究发现:氧化铋和硝酸铋的加入可对锂、锌的化舍物的过量汽化产生有效的抑制作用,而这有利于减小所得铁氧体材料的实际组分偏差.但铋的化合物的加入也会对锂锌铁氧体的低频吸波性能产生略微的减弱效果.     

MnZn功率铁氧体的研究进展及发展趋势

介绍了宽温超低损耗、高频低损耗和高温高饱和磁感应强度(Bs)MnZn功率铁氧体材料的研究现状,以及添加剂的种类和制备方法的研究,世界上主要软磁铁氧体公司近几年的最新产品情况,指出了MnZn功率铁氧体的发展趋势.从目前的发展状况来看,应用在中低频的功率MnZn铁氧体材料不但要求在较宽的温度范围内具有较低的损耗,同时要求具有高的起始磁导率和饱和磁感应强度.而对于高频功率MnZn铁氧体材料则继续向高频低损耗发展.     

锶废渣直接制备锶钡铁氧体材料研究

以重庆市大足区天青石锶废渣为原料,采用化学共沉淀法制备了锶钡铁氧体(Sr_xBa_1-xFe₁₂O₁₉)。通过XRD、SEM对锶钡铁氧体进行表征,探究沉淀pH值、焙烧温度、焙烧时间对锶钡铁氧体物相组成、微观形貌的影响。实验结果表明,在沉淀pH值为12、焙烧温度900℃、焙烧时间2 h的条件下,制备出的锶钡铁氧体无杂相且呈明显的六角或近六角片状形貌,饱和磁化强度(Ms)60.29 Am²/kg,剩余磁化强度(Ms)32.16 Am²/kg,矫顽力(Hc)30.08 kA/m,具有永磁体高饱和磁化强度(Ms)和高矫顽力(Hc)的特性。     

黄钠铁矾渣制备镍锌铁氧体及其表征

利用化学共沉淀法,以黄钠铁矾渣为原料制备镍锌铁氧体。以正丁胺为沉淀剂,在室温条件下,通过共沉淀铁、镍、锌(镍、锌由硫酸锌、硫酸镍按Ni0.5Zn0.5Fe2O4比例补加)制备镍锌铁氧体样品。采用SEM、XRD和FT-IR对该样品进行表征。结果表明,制备所得的样品为镍锌铁氧体。同时,通过磁滞回线显示,镍锌铁氧体比饱和磁化强度为9.04A·m2/kg,比剩余磁化强度为0.65 A·m2/kg,矫顽力为2.47kA/m,具有软磁材料的低比剩余磁化强度和低矫顽力的特性。     

Co1-xZnxFe2O4铁氧体气凝胶的制备及其性能研究

采用醇-水溶液加热法结合超临界流体干燥(SFCD)制备了Co10xZnxFe2O4铁氧体气凝胶,对样品进行了XRD、BET、VSM、ICP及TEM等表征.结果表明.所得铁氧体气凝胶为单一尖晶石结构,具有较高的比饱和磁化强度、较大的矫顽力以及较高的比表面积;在一定范围内,改变Zn含量可以改善CoZn铁氧体气凝胶的性能.     

阴极保护用陶瓷涂层阳极

在钮扣形的99%钝钛和铌基材上等离子喷涂导电性锂铁氧体而制成一种阴极保护用阳极。选择锂铁氧体是因为它在钛和铌基材上具有极好的附着力,而且具有良好的导电性、低溶解速率以及长期稳定性。描述了钛基材在氯化物溶液中的点蚀性状;最差的保护电位为9.66伏。对涂层阳极在恒电流条件下以0.2安/厘米~2的电流密度在电解槽中进行了溶解试验。利用失重测最法测定了锂铁氧体涂层阳极在两个月试验期内的溶解速率,在充气的3.5%氯化钠溶液内测定值为1～2克/安·年。未观察到对涂层的任何损害作用。钮扣形阳极经独到的设计以便于在不排除水的情况下安装在地下管线、船舶或诸如航道闸门和高架贮水槽等水中结构上。     

铁电陶瓷/铁氧体复合材料的相结构与介电性能

研究了铁电陶瓷/铁氧体混合烧结体的相结构与介电性能。在900℃制备出铁电陶瓷/铁氧体复合材料,该复合材料是介电材料相与铁氧体材料相共存的复相陶瓷。铁电陶瓷/铁氧体复合材料的介电性能在低温区域主要是介电材料相起作用,而铁氧体材料主要在高温部分对复合材料的介电性能起作用。采用两相混合分布的介电常数计算公式拟合了复相陶瓷的介温曲线,并提出修正指数因子α和β,建立修正方程。      

移相器材料Zn、Ti、Sn替代锂铁氧体

为了研制高性能自动跟踪同步通信卫星相控天线阵中的移相器材料,采用普通陶瓷工艺,并加入微量杂质：Bi₂O₃、NiO、Co₂O₃和MnCO₃,且利用氧气氛烧结制备了目前尚未见报道的铁氧体Li_0．625Zn_0．1Ti_0．25Sn_0．1Fe_1．925O₄．结果表明,该材料具有较高的居里温度和较低的介电损耗.并对锂铁氧体Li_0.5（1-y）Zn_yFe_{2.5（1-0.2y）}O₄的微波特性进行了讨论.     

Design of drop-in microstrip circulator

The operation of a ferrite drop-in circulator is theoretically predicted and experimentally confirmed. The cavity model is applied both to the ferrite disc and the dielectric region directly below the ferrite disc. The standing-wave condition required by the dielectric cavity plus the two ferrite circulation conditions determine uniquely three design parameters for the circulator: the magnitude biasing field, the radius of the ferrite disc, and the dielectric constant of the dielectric sleeve surrounding the ferrite disc. In addition, the characteristic impedance of the microstrip feeder lines was purposely designed for 50 Ω in order to eliminate the need for impedance transformers. We found that for a thin dielectric substrate with dielectric constant smaller than that of the ferrite, the circulation frequency can be slightly above FMR resonance. Three circulators were fabricated using design parameters calculated by our theory. The measurements are in reasonable agreement with predicted performance of the device     

铁电陶瓷/铁氧体叠层共烧体的介电特性

采用电介质物理学等效电路分析方法研究了Pb(Ni1/3Nb2/3)O3基铁电陶瓷与NiZnCu铁氧体叠层共烧体的介电频率响应,探讨了共烧体界面对介电性能的影响.结果表明,叠层共烧体的介电常数随频率的增加而减小,介电损耗随着频率的增加先增大后减小,有明显的损耗峰出现;界面扩散层对叠层共烧体电学响应有影响,叠层共烧体等效电路可视为介电材料层、铁氧体材料层和界面扩散层C re-R re等效电路的串联,并且界面扩散层会对叠层共烧体低频部分的介电响应起作用.     

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.     

High-frequency dielectric behaviour of Li–Mg ferrites

Dielectric properties such as dielectric constant (ε′) and dielectric loss tangent (tanδ) of mixed Li–Mg ferrites have been measured at room temperature in the frequency range 1 to 13 MHz using an HP 4192A impedance analyser. Plots of dielectric constant (ε′) vs. frequency show a normal dielectric behaviour of spinel ferrites. The frequency dependence of dielectric loss tangent (tanδ) is found to be abnormal, giving a peak at certain frequency for all mixed Li–Mg ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent.     

Dielectric properties of Al-substituted Co ferrite nanoparticles

A series of polycrystalline spinel ferrites with composition, CoFe_2−x Al _x O₄ (0 ≤ x ≤ 1), have been synthesized by sol-gel method. The effect of Al-substitution on structural and dielectric properties is reported in this paper. X-ray diffraction analysis revealed the nanocrystalline nature in the prepared ferrite samples. The particle size, D, decreases with increase in Al-content. The lattice parameter, a and X-ray density, d _x , decreased with increase in Al-content. The dielectric properties for all the samples have been studied as a function of frequency in the range 100 Hz–10 MHz. Dielectric properties such as dielectric constant, ɛ′, dielectric loss, ɛ″ and dielectric loss tangent, tan δ, have been studied for nanocrystalline ferrite samples as a function of frequency. The dielectric constant and dielectric loss obtained for the nanocrystalline ferrites proposed by this technique possess lower value than that of the ferrites prepared by other methods for the same composition. The low dielectric behaviour makes ferrite materials useful in high frequency applications.     

CaCu3Ti4O12/NiCuZn铁氧体基磁电复合材料研究

将CCTO(CaCu3Ti4O12)与NiCuZn铁氧体进行复合,系统地研究了组分变化对这种新型磁电复合材料的烧结性能、晶相结构、显微结构和磁电性能的影响。随后,为了实现复合材料的低温烧结以及综合考虑复相陶瓷的磁电性能,选取80%(质量分数,下同)NiCuZn铁氧体/20%CCTO组分,以BBSZ(Bi2O3-H3BO3-SiO2-ZnO)玻璃作为助熔剂,研究了CCTO/NiCuZn铁氧体基复合材料的烧结行为和磁电性能。结果表明,掺杂BBSZ后,900℃下烧结的所有样品的密度均达到了复相陶瓷理论密度的95%,且复相陶瓷的介电常数和磁导率在1～30 MHz范围内均不依赖于频率的变化。在10 MHz的频率下,当BBSZ的含量从0增加到3%时,复相陶瓷磁导率μ从13.2增加到47.9,磁损耗tanδμ从0.022下降到0.017,同时,样品的谐振频率从109Hz左右移动到3.2×108Hz。相应地,复相陶瓷的介电常数ε从9.2增加到16,介电损耗tanδε从0.069下降到0.012。这一优异的整体性能使其有望实际应用。     

0.3–3 GHz magneto-dielectric properties of nanostructured NiZnCo ferrite from hydrothermal process

A simple hydrothermal route with cetyltrimethylammonium bromide was proposed for directly synthesizing single-crystalline NiZnCo ferrite at 160 °C. X-ray diffraction patterns and micrographs indicate that products consist of spinel ferrite nanocrystals. The dielectric constant of NiZnCo ferrite is about 11 and the imaginary part of complex permittivity is 1.3. The saturation magnetization of Ni_0.54Zn_0.48Fe_1.98O₄ increases from 41.36 to 73.9 emu/g for Ni_0.55Zn_0.46Fe_1.98O₄ with a cobalt stoichiometry of 0.01. The real part μ′ of complex permeability for NiZnCo ferrite reaches 3 at 1 GHz. The imaginary part μ″ of NiZnCo ferrite has values higher than 1.2 within 0.7–3 GHz. Through the incorporation of the magnetic fillers, the low dielectric constant of the composites may meet the requirements of impedance matching to achieve maximal absorption of the electromagnetic energy in GHz frequency range.     

Studies on dielectric and magnetoelectric behavior of 25% CMFO ferrite and 75% BZT ferroelectric multiferroic magnetoelectric composites

In the present work, multiferroic magnetoelectric (ME) composites of ferrite and ferroelectric phases are prepared. Here, the magnetostrictive (ferrite) phase, Co_1.2 − yMn_yFe_1.8O₄ (y = 0.0 to 0.4) i.e. CMFO is synthesized by chemical combustion route and the piezoelectric (ferroelectric) phase, BaZr_0.08Ti_0.92O₃ i.e. BZT is synthesized by conventional ceramic method. Frequency dependent dielectric constant measurement from 20 Hz-1 MHz at room temperature shows usual dielectric dispersion behaviour, which may be attributed to the Maxwell-Wagner type interfacial polarization. Temperature dependent dielectric constant measurement shows two dielectric maxima, one below 100 °C and the second above 500 °C. The dielectric maxima below 100 °C corresponds to the transition temperature of the ferroelectric phase and that of above 500 °C corresponds to the transition temperature of the ferrite phase of the ME composites. It is observed that as Mn content increases in the cobalt ferrite, the phase transition temperature of the ferrite phase decreases. The static magnetoelectric voltage coefficient was measured as a function of intensity of the applied dc magnetic field. These magnetoelectric composites may have possible applications in magnetic field sensing probes and linear ME devices.