Spin-Polarized Tunnelling Magnetoresistance Effects in La0.833K0.167MnO3／SrTiO3 Polycrystalline Perovskite Manganites

A sample of La0.833K0.167MnO3-SrTiO3 (LKMO/STO) is fabricated by the sol-gel method. The microstructure,magnetic and transportation properties have been studied. X-ray diffraction patterns indicate that the structure of LKMO/STO is a homogeneous solid solution phase. The resistivity of LKMO/STO shows the insulator behaviour, which is different from La0.833K0.167MnO3 (LKMO) whose resistivity shows metal-insulator transition with decreasing temperature. The low-field (moH = 0.02 T) magnetoresistance decreases from 11% to 0.2% with the increasing temperature from 4 K‘to 220K for the LKMO/STO sample. The magnitude of magnetoresistance in a strong field (μoH = 5.5 T) almost increases linearly with decreasing temperature and reaches the maximum of 65% at the low temperature of 4.2K, which is much higher than that oE LKMO (40%). The enhanced low-field magnetoresistance effects are quantitatively explained by the spin-polarized tunnelling at grain boundaries.     

Cu-MgF2复合纳米金属陶瓷薄膜的电导特性研究

用射频磁控共溅射法制备了Cu体积分数分别为 10 % ,15 % ,2 0 %和 3 0 %的Cu MgF2 复合金属陶瓷薄膜 .用x射线衍射、x射线光电子能谱和变温四引线技术对薄膜的微结构、组分及电导特性进行了测试分析 .微结构分析表明 :制备的Cu MgF2 复合薄膜由fcc Cu晶态纳米微粒镶嵌于主要为非晶态的MgF2 陶瓷基体中构成 ,Cu晶粒的平均晶粒尺寸随组分增加从 11 9nm增至 17 8nm .5 0— 3 0 0K温度范围内的电导测试结果表明 :当Cu体积分数qM 由 15 %增加到 2 0 %时 ,Cu MgF2 复合薄膜的电阻减小了 8个量级 ,得出制备的复合薄膜渗透阈qCM 应处于 15 %和 2 0 %之间 .qM 在 10 %和 15 %之间的薄膜呈介质导电状态 ,而在 2 0 %和 3 0 %之间的薄膜则呈金属导电状态 .从理论上讨论了复合薄膜中杂质电导和本征电导的激活能及其对电导的贡献 ,并讨论了Cu MgF2 复合纳米金属陶瓷薄膜的渗透阈 ,得到了和实验一致的结果     

Bi（2223）厚膜微结构分析

测量了预结厚膜在不同压力下的密度，用ＳＥＭ观测了三次烧结扣揭去银的银夹板厚膜、银包套厚膜的厚度和表面、横截面的形貌，实验结果表明，厚膜的临界电流密度比单晶中的临界电流密度低两个量级的原因可能是；在制备过程中粉末内存在的空气，在烧结时产生的空洞而导致厚膜的织构和晶粒间的连接变差，提出了降低空洞、提高厚膜临界电流密度的方法。     

Ni-SDC固体氧化物燃料电池阳极的合成和性质

采用柠檬酸-硝酸盐溶胶-凝胶低温自蔓延燃烧法制备氧化镍（NiO）粉末和Ce0.8Sm0.2O1.9（SDC）粉末，并将NiO与SDC按不同质量比和不同制备工艺制备了固体氧化物燃料电池（SOFC）的阳极前身。再用自组装的还原装置将其在820℃经2．5h还原后，采用四端子法测量其电导率值。分析了阳极片电导率与阳极片微结构、Ni的质量百分数、混合研磨时间及烧结温度之间的关系。结果显示，阳极片的电导率强烈依赖于镍含量和制备工艺。     

交换耦合稀土永磁微观结构优化及其实现途径

针对纳米复相永磁材料发展中存在的问题, 阐述了交换耦合作用及其对微观结构的要求.在微观结构的优化方面提出了一些思路, 并介绍了成分优化和制备工艺优化(熔炼、快淬及晶化)等实现途径, 以更好地发挥该材料潜在的高性能.     

太空(FeNi)金属熔体凝固的时空图象和结晶机理研究

岩庄陨石冲击重熔再结晶(FeNi)金属颗粒的微结构研究发现,四同心环生长结构是远离热力学平衡态的太空(FeNi)金属熔体凝固的基本时空图象。四同心环结构的快速生长和相互作用导致八面体(FeNi)金属枝晶的形成。四同心环晶体生长方式可能是太空环境下(FeNi)金属熔体结晶形成八面体铁陨石的一种基本方式。     

甲基丙烯酸-3-三甲氧基硅丙酯/苯乙烯共聚乳胶粒微结构

我们曾制备了核-壳结构的杂化乳胶粒, 并用溶剂将核去除得到杂化空心微胶囊. 但由于此乳液聚合过程十分复杂, 在不同条件下反应得到乳胶粒的微结构有较大不同, 目前尚未见到各反应条件下所得产物微结构的表征和形成机理的研究报道. 本文将系统分析在不同反应条下, MPS和St种子乳液聚合过程中, 得到的乳胶粒壳层杂化聚合物的微结构, 并研究了其形成原因.     

三段加热系统对大尺寸MPOF预制棒一步拉伸工艺

采用自行设计的微结构聚合物光纤专用拉丝系统对大尺寸微结构聚合物光纤预制棒的一步拉伸工艺进行了研究.该微结构聚合物光纤加热系统采用三段式梯度加热,可保持炉内温度的控制准确度在±2℃以内.在保持送料速度与牵引速度恒定、协调的条件下,通过对温度场温度梯度控制优化,确定了最佳拉丝温度组合,并得到了直径规格310 μm、标准偏差为±20 μm的较高质量的微结构聚合物光纤.     

蜘蛛丝Ⅱ：分级微结构与跨尺度力学

介绍了蜘蛛丝由普通蛋白质和弱的化学键连接的独特微结构,以及它将普通力学性能的材料,通过从微观到宏观多级自组装,获得同时具有高强度和高延展性的超级力学性质的跨尺度力学原理. 同时也介绍了蜘蛛丝在纳米尺度的微结构优化及其应力应变曲线的独特的线弹性-软化-硬化性质. 第Ⅲ 部分将继续介绍这种应力应变曲线对建造的具有超级抗损伤和超级带缺陷工作能力的蜘蛛网的作用.     

硬脂酸镉和山嵛酸镉混合LB膜的微结构

X-ray diffraction (XRD) was used to investigate the microstructure and phase separation of mixed multilayers of cadmium stearate (SA) and behenate (BA) deposited onto hydrophilic glass by the Langmuir-Blodgett technique. No unitary fatty acid diffraction peaks in the XRD spectra of the mixed LB films, which reveals that domains in these samples are small and uniform. The interplanar spacing of the mixed LB films changes with the ratio of BA to SA in a step-shaped curve, which suggests that with the changing of the ratio between BA and SA, only three kinds of ordered structure form in the mixed system, and each microstructure, in particular, the short chains against long chains meshed microstructure can be maintained in a certain ratio range . In addition, for the meshed microstructure, the alkyl chains of both SA and BA stand straight or may have exactly the same small tilted angle from the substrate normal, as is indicated by the symmetric and asymmetric stretching vibration of methylene (CH2) peaks which are at 2847.80 and 2914.37 cm-1respectively in the Fourier transform infrared (FT-IR) transmission spectra. The mixed system always goes through a longitudinal regularity decreasing process when BA/SA is out of the intermediate ratio range (BA/SA: 1/5-1/1), which is illustrated by the relative XRD intensity changing with the ratio of BA/ SA in a \W" shape. These results for the mixed LB films of BA/SA provide meaningful data for choosing the mixture ratio when fabricating composite films with special structure.