立方A^4＋M^5＋2O7型化合物与新型负热膨胀材料

概述了立方Ａ＾４＋Ｍ＾５＋２Ｏ７型化合物的结构特点，讨论了ＡＶ２－ｘＰｘＯ７型（Ａ＝Ｚｒ或Ｈｆ；ｘ＝０．１～１．２）及其部分取代的Ａ＾４＋１－ｙＢ＾４＋ｙＶ２－ｘＰｘＯ７型（Ｂ＝Ｔｉ，Ｃｅ，Ｔｈ，Ｕ，Ｍｏ，Ｐｔ，Ｐｂ，Ｓｎ，Ｇｅ或Ｓｉ；ｙ＝０．１～０．４）和Ａ＾４＋１－ｙＣ＾１＋ｙＤ＾３＋ｙＶ２－ｘＰｘＯ７型（Ｃ为碱金属元素，Ｄ为稀土金属元素）材料的负热膨胀性能。     

钙钛矿型复合氧化物催化剂中过渡金属离子的状态及其间的相互作用

讨论了Ｂ位二元复下钛矿型复合氧化物ＬａＭｙＭ＇１－ｙＯ３（Ｍ，Ｍ＇＝Ｍｎ，Ｆｅ，Ｃｏ；ｙ＝０．０￣１．０）中过渡金属离子的状态及其间的相互作用。在Ｍｎ－Ｃｏ复合体系中，富锰区（ｙ〉０．５）Ｍｎ＾３＋－Ｏ＾２－－Ｍｎ＾４＋的铁磁超交换作用对样品的磁性起决定作用。富钴区（ｙ〉０．５）Ｃｏ＾２＋和Ｃｏ＾ＩＩＩ离子的存在及其浓度是影响磁性和电导性的主要因素。ｙ＝０．５时样品的结构决定了样品的强铁磁性质。在     

EMC用大损耗NiCuZn铁氧体吸收瓦材料研究

３０～１０００ＭＨｚ铁氧体吸收瓦（尺寸为１００ｍｍ ×１００ｍｍ×厚度）在电磁兼容（ＥＭＣ）领域具有广泛的应用。本文采用氧化物工艺制备ＮｉＣｕＺｎ尖晶石铁氧体,测试并分析了用Ｃｕ２＋取代Ｎｉ２＋及Ｃｏ２＋掺杂对材料复磁导率的影响。在９００℃／２ｈ预烧,１１５０℃／２ｂ烧结,得到ＮｉＣｕＺｎ铁氧体相对复磁导率（μｒ＝μ′ｒ－ｊμ″）μ＇ｒ＞１１０,μ″ｒ＞２００（频率ｆ＝３００ＭＨｚ）;通过对该材料优化设计,当铁氧体吸收瓦厚度 ｄ＝５．５ｍｍ,在 ３０～１０００ＭＨｚ,反射率 Ｒ＜－１２ｄＢ,在 ｆ＝５０～８００ＭＨｚ,Ｒ＜－１５ｄＢ。     

熔盐法合成BaFe11Co0.5Ti0.5O19磁性粉体及其性能分析

采用熔盐法制备了六角晶系结构钡铁氧体ＢａＦｅ１１Ｃｏ０．５Ｔｉ０．５Ｏ１９。Ｘ射线衍射和热分析测量表明，合成反应过程在８５０℃下完成。粉料的磁性能测量和粉料的粒度及颗粒形态表明，熔盐法合成的粉料适合作为高性能磁记录材料。     

熔盐法合成BaFe_（11）Co_（0．5）Ti_（0．5）O_（19）磁性粉体

采用熔盐法制备了六角晶系结构钡铁氧体ＢａＦｅ（１１）Ｃｏ（０．５）Ｔｉ（０．５）Ｏ（１９）。Ｘ射线衍射和热分析测量表明，合成反应过程在８５０℃下完成。粉料的磁性能测量和粉料的粒度及颗粒形态表明，熔盐法合成的粉料适合作为高性能磁记录材料。     

B位掺杂对（Pb,Ca）（Fe1／2Nb1／2）O3陶瓷微波介电性能的影响

研究了Ｂ位分别掺杂Ｓｎ＾４＋、Ｚｒ＾４＋、Ｃｅ＾４＋对（Ｐｂ０．４５Ｃａ０．２５）（Ｆｅ１／２Ｎｂ１／２）Ｏ３（ＰＣＦＮ）陶瓷的烧结行为、微观结构及微波介电性能的影响。实验结果表明,掺杂样品能在相对较低的温度下烧结（１２００℃／２ｈ）,Ｂ位大半径离子的掺入使介电常数降低,适量的Ｂ位掺杂能不同程度的改进ＰＣＦＮ陶瓷的综合微波介电性能。用这种材料做成的带通滤波器在中心频率为９２８．４ＭＨｚ下,插入损耗为２．４６９ｄＢ,满足插入损耗应小于３ｄＢ的要求,在移动通信中有着实际应用前景。     

Li1+2x+yAlxNdyTi2-x-ySixP3-xO12系统的锂快离子导体研究

Ｌｉ１＋２ｘ＋ｙＡｌｘＮｄｙＴｉ２－ｘ－ｙＳｉｘＰ３－ｘＯ１２锂快离子导体可以用精选的天然高岭石Ａｌ４「Ｓｉ４Ｏ１０」（ＯＨ）８为起始原料，经与Ｌｉ２Ｃｏ３、ＴｉＯ２、ＮＨ４Ｈ２ＰＯ４进行高温（８００－１０００℃固相反应约２０ｈ而制得，一个空间群属于Ｒ３Ｃ的固溶体导电相可在ｙ＝０．５，ｘ≤０．３和ｙ＝１．０，ｘ≤０．４的组成范围内发现，该盯具有较好的电导性较低的活化能，起始组成ｙ＝１．０，ｘ＝０．     

La1-xCaxFe1-yCoyO3对氧气还原的催化活性

为了提高燃料电池、金属－空气电池中氧电极的性能,本工作合成了Ｌａ１－ｘＡ′ｘＦｅ１－ｙＣｏｙＯ３（Ａ′＝Ｃａ、Ｓｒ、ＢＡ）,作为氧气还原的催化剂,制成了氧电极,在碱性介质中以Ｈｇ／ＨｇＯ为参比电极测量了电极的极化曲线,考察了组成催化剂的电催化活性和化学稳定性的影响。用ＢＥＴ法测量了催化剂的表面积,发现ｘ＝０．４时,催化剂的比表面积最大,同时电催化性能也最强,本工作表明Ｌａ０．６Ｃａ０．４Ｃｏ０．４     

应用量子化学研究Ca2Fe2—xAl2O5的水化活性

用量子化学ＳＣＣ－ＤＶ－Ｘα方法分析了Ｃａ２Ｆｅ２－ｘＡｌｘＯ５体系听ａ２Ｆｅ２Ｏ５，Ｃａ２Ｆ３１．４３Ａｌ０．５７Ｏ５和Ｃａ２Ｆ３１．２８Ａｌ０．７２Ｏ５，认为它们的水化活性随Ａｌ的增加而提高的原因是：（１）Ａｌ的净电荷比Ｆｅ高，易吸收水分子的弧对电子；（２）Ａｌ－Ｏ键比Ｆｅ－Ｏ键弱，易断裂而容易与水反应。     

不同热化学还原LiNbO_3：Ti或Mn晶体杂质电荷态和点缺陷

采用光学吸收和电子顺磁共振（ＥＳＲ）技术表征不同热化学还原ＬＩＮｂＯ３：Ｔｉ，Ｍｌｉ（ＬＮ：Ｔｉ，Ｍｎ）和纯的Ｌｉ／Ｎｂ＝０．９４５一致熔化ＬｉＮｂＯ３（ＬＮ）晶体的热力学还原习性．将ＬＮ：Ｔｉ（厚度为１ｍｍ）样品放在Ｌｉ２ＣＯ３中、６００℃、保温７ｈ，产生６９０ｕｒｎ（～１．８ｅＶ，Ｔ＝６７％）和峰值靠近７８５ｎｍ（Ｔ＝７１％）的７７０￣８１０ｎｍ光学吸收带，它们分别对应于Ｔｉ（３＋）的２Ｔ→２Ｅ跃迁以及室温稳定Ｆ＋心滞有一个电子的氧空位）．经真空１．２Ｐａ，８００℃２ｈ还原后，存在峰值为６７５ｎｍ（Ｔ＝５２％）的４８０～７８０ｎｍ平滑吸收带，它们是Ｔｉ（３＋）、Ｆ心和Ｆ＋心重叠吸收，但是，在Ａｒ气氛下、９００℃、８ｈ处理后，仅能看到峰值在６７５ｎｍ（Ｔ＝５２％）的６００～７８０ｎｍＴｉ（３＋）的弱吸收．来自未处理ＬＮ：Ｔｉ晶体的室温和Ｘ带的ＥＳＲ＄观察到ｇ＝４．３４８，共振磁场０．１５２ＴＨ（ｐ－ｐ）＝０．０１６３Ｔ微波吸收峰，以及四组精细结构Ｂ线（每一ｆｓ线是由６条超精细结构ｈｆｓ组成），ｇ值从３．４６０～１．６７９吸收，它们分别归为于晶体杂质Ｆｅ（３＋）和Ｍｎ（２＋）离子．真空还原后，Ｆｅ（３＋）的     

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。     

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。     

纳米钡铁氧体吸波材料的研究进展

介绍了钡铁氧体纳米材料的吸波机制,以及钡铁氧体纳米材料在制备以及吸波方面的研究进展,重点介绍了金属离子替代(Co、Ti、Zn、Cr和Al等)对钡铁氧体结构和吸波性能方面的研究.     

Co含量对轻质微波吸收剂C/Co纳米纤维吸波性能的影响

采用静电纺丝法结合热处理制备了一种可应用于2~18 GHz频段的高性能轻质微波吸收剂C/Co纳米纤维, 详细研究了金属Co含量对纳米纤维的电磁特性及微波吸收性能的影响。相对于纯碳纳米纤维, C/Co纳米纤维的微波吸收性能得到显著加强, 其主要吸波机制仍是介电损耗。随着Co含量的增加, C/Co纳米纤维的电磁衰减能力逐渐下降, 而微波吸收却先增强后减弱, 含37.8wt% Co的C/Co-5纳米纤维因金属Co粒子和纳米碳纤维的良好结合与协同效应, 以及纤维中特殊的Co粒子@石墨核壳结构所带来的良好阻抗匹配与足够高的电磁衰减能力而表现出最好的吸波性能。模拟计算结果表明, 涂层厚度在1.1~5.0 mm间变化时, 填充5wt% C/Co-5纳米纤维的硅胶吸波涂层的反射损耗(RL)值超过-20 dB的频率范围在3.2~18 GHz, 最小RL值达到-78.8 dB, 其中当涂层厚度仅为1.5 mm时, RL值低于-20 dB的吸收带宽可达6.0 GHz (12~18 GHz)。C/Co纳米纤维优异的微波吸收性能表明, 这些磁性碳杂化纳米纤维有望成为一种极具应用前景的新型吸波材料。     

A crystallization conditions study of the Ti‐doped barium hexaferrite powders synthesized with the glass crystallization technique for microwave applications

For microwave applications Titanium doped M‐type hexagonal ferrites have been synthesized by means of glass crystallization technique varying the crystallization parameters and the melt doping concentrations. The chosen melt dopings were x = 5.4 and 7.2 mole‐% TiO₂ with the following basic composition (mole‐%): 40 BaO + 33 B₂O₃ + (27‐x) Fe₂O₃ + x TiO₂. We have studied the dependencies between the magnetic properties, the valence of the iron ions in the glasses and the powders, the formation of new dielectric phases and the microwave absorption. After the Ti⁴⁺ ions substitutions, the magnetocrystalline anisotropy changed, this effect was observed in the static magnetic properties (_JH_C and M_S) measured using a vibration sample magnetometer. Furthermore the Ti⁴⁺ ions preferably occupy mainly the 2a as well as slightly the 2b sites in the lattice of the barium hexaferrite, which are studied using Mössbauer spectroscopy. Besides, the X‐ray diffraction studies proved that the formation of the ferrimagnetic (BaFe_12‐xTi_xO₁₂) and dielectric (BaTi₆O₁₃) phases are dependent on the crystallization parameters. The controlled influencing of lattice sites occupation and of the Fe²⁺ content in the ferrimagnetic phase as well as the controlled formation of the dielectric phase rate during the annealing are possibilities to optimize the microwave absorption of Ti‐doped barium hexaferrite powders synthesized by glass crystallization technique.     

Regulation of Impedance Matching and Dielectric Loss Properties of N-Doped Carbon Hollow Nanospheres Modified With Atomically Dispersed Cobalt Sites for Microwave Energy Attenuation

The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M–SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M–SAs. However, the simultaneous engineering of the morphology and electronic structure of M–SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co–SAs on N-doped hollow carbon spheres (NHCS@Co–SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co–SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8 wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co–SAs are up to −44.96 dB and 5.25 GHz, respectively, while the absorbing thickness is only 2 mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M–SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co–SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers.     

Synthesis, Characterization and Electromagnetic Studies on Nanocrystalline Co0.5Zn0.5Fe2O4 Synthesized by Polyacrylamide Gel

Nanocrystalline Co0.5Zn0.5Fe2O4 ferrite was synthesized by polyacrylamide gel method. The electromagnetic and microwave absorption properties of the ferrite were investigated. The results indicated that calcining temperature of the ferrite had a significant influence on the effective properties of the ferrite. When the calcining temperature was 500, 600 and 700℃, the average size of particles was 10, 30 and 80 nm, respectively. The dielectric loss （ε″） and magnetic loss （μ″） of the ferrite was around 0.65 and 0.29 at 8.2 GHz, respectively. Microwave absorption properties of the ferrites were simultaneously influenced due to the strong correlation between reflection loss and electromagnetic parameters of the ferrite.     

超声场下导电聚苯胺/纳米铁氧体吸波涂层的制备及其吸波性能

导电聚苯胺/纳米铁氧体复合吸波材料具有吸波能力强,质量轻等特点.采用乳液聚合法以苯胺为单体、十二烷基苯磺酸为掺杂剂、过硫酸铵为氧化剂,在超声场下制备导电聚苯胺粉体;将其与纳米Ni0.5Zn0.5Fe2O45及纳米Co0.5Zn0.5Fe2O4一起用原位合成法制备了复合吸波涂层.结果表明:制备的吸波涂层在17.9,15.9,22.3 GHz时分别具有最大反射损耗-10.0,-15.9,-39.9 dB,2种复合涂层拓展了波段,提高了对电磁渡的吸收效果.     

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.     

(Ba1-xSrx)La4Ti4O15（x=0.8～0.95）陶瓷的微结构及微波介电性能研究

采用固相反应法制备了(Ba1-xSrx)La4Ti4O15(x=0.8~0.95)复合体系微波介质陶瓷,并对其进行物相组成、晶体结构分析以及微波介电性能的研究.研究结果表明,(Ba1-xSrx)La4Ti4O15陶瓷主晶相为SrLa4Ti4O15,并伴随有第二相SrLa8Ti9O15.SEM观察表明,Ba0.2Sr0.8La4Ti4O15陶瓷内部微观结构致密,晶粒尺寸在10~20μm之间,晶界清晰.随着x值逐渐增大,(Ba1-xSrx)La4Ti4O15陶瓷中晶粒形态发生变化,气孔增多.在x=0.8时,(Ba1-xSrx)La4Ti4O15陶瓷具有优良的微波介电性能,即εr=40.86,Q×f≈62806 GHz,τf=20×10 6/℃.随着Ba2+的含量逐渐增加,该陶瓷的介电常数εr单调上升,品质因子Q×f值增加,说明适量的Ba2+替代Sr2+能改善陶瓷的微波介电性能.