Room-temperature ferroelectricity in strained SrTiO3

Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance. An alternative way to adjust T(c) in ferroelectric films is strain. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T(c) by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T(c) is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon(r) at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications.     

脉冲微波式氢原子钟初步结果

通过向原子钟微波腔内导入相干的脉冲微波信号,同时设置适当的脉冲信号参数,可以激发原子共振跃迁的Ramsey条纹,利用其中心条纹作为钟跃迁可以极大地压缩原子钟的谱线宽度,有望提高原子钟的电性能指标.该项技术已经在pop铷钟上得到应用,成功压缩了铷原子的共振谱线线宽.中国科学院上海天文台在被动型氢原子钟物理系统的基础上,开展了氢原子微波脉冲激励技术的研究,设计了微波脉冲扫频电路,目前已经初步观测到氢原子的Ramsey条纹,从而证明了该项技术用于氢原子钟的可行性.计划优化系统和微波信号参数,从而进一步压缩原子线宽.同时设计完善的伺服电路,实现原子钟的环路锁定,形成脉冲微波式氢原子钟,并测试和优化了整机性能指标.     

室温离子液体在色谱中的应用

近来室温离子液体广泛应用于分析化学的各个领域.就近年来咪唑类室温离子液体在气相色谱、液相色谱、胶束电动色谱、毛细管电泳等色谱分析中的应用研究进行综述.     

几种常温自交联丙烯酸树脂非水分散体的制备

采用化学转化法将水乳液转化为非水乳液是制备非水分散体的一种方法。根据实时需要，将常温自交联丙烯酸树脂乳液转化为非水分散体，这种材料可用于文物保护工作。     

室温固化聚氨酯胶黏剂的研制

研制了一种室温固化无溶剂双组分聚氨酯胶黏剂,具有较高的黏接强度及良好的韧性,在保持室温剪切强度为37.1MPa的同时,扯断伸长率为104％,200℃仍有3．8MPa的强度;分析并详细探讨了硬段含量不同体系性能的变化：通过对热失重曲线及恒温失重的考察表明体系具有良好的耐热老化性能,同时考察了体系的耐水性及耐油性,结果表明体系具有优异的耐介质性能。     

Room-temperature ferroelectricity in supramolecular networks of charge-transfer complexes

Materials exhibiting a spontaneous electrical polarization that can be switched easily between antiparallel orientations are of potential value for sensors, photonics and energy-efficient memories. In this context, organic ferroelectrics are of particular interest because they promise to be lightweight, inexpensive and easily processed into devices. A recently identified family of organic ferroelectric structures is based on intermolecular charge transfer, where donor and acceptor molecules co-crystallize in an alternating fashion known as a mixed stack: in the crystalline lattice, a collective transfer of electrons from donor to acceptor molecules results in the formation of dipoles that can be realigned by an external field as molecules switch partners in the mixed stack. Although mixed stacks have been investigated extensively, only three systems are known to show ferroelectric switching, all below 71 kelvin. Here we describe supramolecular charge-transfer networks that undergo ferroelectric polarization switching with a ferroelectric Curie temperature above room temperature. These polar and switchable systems utilize a structural synergy between a hydrogen-bonded network and charge-transfer complexation of donor and acceptor molecules in a mixed stack. This supramolecular motif could help guide the development of other functional organic systems that can switch polarization under the influence of electric fields at ambient temperatures.     

室温自交联型TF弹性防水涂料性能研究

以自制的弹性丙烯酸聚合物乳液为基料，制备得到TF弹性防水涂料，并对其性能进行了研究。结果显示，TF弹性防水涂料具有优良的耐低温性能和耐粘污性能，并表现出较好的弹性体性质，其断裂伸长率在-10～30℃范围内基本保持不变。此外，具有室温自交联性质的TF弹性防水涂料在裂纹桥连和耐腐蚀方面也具有较好的优势，综合性能突出。     

室温磁致冷复合工质材料的研制

采用铜包套包覆轧制工艺制备出了室温磁致冷工质Ｇｄ＿（１－ｘ）Ｔｂ＿ｘ的实用复合工质薄带。薄带表面光滑厚度均匀，具有良好的室温磁热熵效应。对制备工艺条件及若干影响磁热熵效应的因素进行了较详细的分析。     

水超脉泽源：[OIV]发射线和脉泽辐射

水超脉泽辐射光度很大,因此活动星系核被公认为是其唯一的能源,而近来[OIV]发射线被认为可以准确地示踪活动星系核各向同性的强度．为了分析活动星系核和脉泽辐射间的内在联系,对所有发表的水脉泽星系的（OIV]发射线观测资料进行了全面调研和收集．整个脉泽样本和3个恒星形成脉泽的[oIV]线的平均光度分别为10^7.09±0....     

La0.75Sr0.25-xCuxMnO3块体材料的室温磁电阻效应

采用溶胶-凝胶法(sol-gel)制备了名义组分为La0.75Sr0.25-xCuxMnO3(x=0,0.03,0.05,0.07)的块体样品.采用DMAX-RB(12kW)旋转阳极X射线衍射仪对材料进行了晶体结构的研究.结果显示,样品呈单相菱面体钙钛矿结构.通过研究样品的磁特性及庞磁电阻性质发现,在掺入适量Cu离子后,样品的居里温度TC随Cu含量增加逐渐降低,而样品的庞磁电阻效应有了明显的改善.     

室温固化无溶剂双组份聚氨酯结构胶的研究

合成了4种相对分子质量和官能度各不相同的聚酯多元醇,并与MDI反应合成了端羟基及端异氰酸基预聚体,通过红外光谱对其结构进行了表征.研究了不同端羟基化合物与端异氰酸基化合物所构体系的粘接性能、热老化性能及热失重情况,结果表明该体系室温剪切强度为35~40 MPa,80℃,100℃和200℃剪切强度可达12~16 MPa,6~8 MPa和3~5 MPa,90°剥离强度为5~7 kN/m,T5最高为286℃,加入石棉后体系的高温剪切强度及耐热老化性能都得到提高.     

室温离子液体及其在绿色化学中的应用

~~烷基取代咪唑阳离子 (图 1 )研究最多 ,表 1总结了近年来开发研究的此类阳离子的种类及结构 .可以组成室温离子液体的阴离子 ,目前的研究除 Al Cl4-,NO2 -和干燥时易爆的 NO3 -,Cl O4-外 ,含氟阴离子为多 ,主要有 :BF4-,PF6-,As F6-,Sb F6-,F ( HF ) n-,CF3 SO3 -,CF3 CF2 CF2 CF2 SO3 -,( CF3 SO2 ) 2 N-,( CF3 SO2 ) 3 C-,CF3 COO-,CF3 CF2 CF2 COO-等 .图 1　烷基取代咪唑阳离子　　由各种阳离子和各种阴离子组合 ,可以得到一系列特性各异的室温离子液体 ,目前已报道的多为由表 1所示的烷基咪唑阳离子和含氟阴…     

河外水脉泽源的红外特性

收集了最新的河外水脉泽样本资料(截至2007.03),并计算给出这些源的部分物理参数.主要分析了水脉泽辐射和脉泽寄主星系的红外辐射之间的可能相关性.分析结果显示河外水脉泽源与银河系内脉泽源一样,水脉泽辐射光度和脉泽寄主星系的红外辐射光度存在相关性,即LH2O~10-9LFIR.     

北斗导航卫星氢原子钟性能分析评估

星载原子钟是导航卫星最重要的载荷之一,负责星上时间基准的产生和维持.我国北斗三号导航试验卫星首次配置了23 kg级被动型星载氢原子钟,验证了氢原子钟的空间环境适应性和在轨性能,实现在轨运行误差小于1 ns/d.在北斗三号全球导航卫星系统中,氢原子钟已作为主钟应用至GEO,IGSO和MEO三类导航卫星,对系统的运行发挥至关重要的作用.本文从氢原子钟的机理和性能评估方法出发,比较了铷钟、铯钟和氢钟三类原子钟的性能差异,根据地面和在轨测试数据,给出氢原子钟在轨运行性能评估结果;最后利用卫星遥测数据建模,对氢原子钟健康状况和寿命进行了初步分析.     

Room-temperature ferromagnetic nanotubes controlled by electron or hole doping

Nanotubes and nanowires with both elemental (carbon or silicon) and multi-element compositions (such as compound semiconductors or oxides), and exhibiting electronic properties ranging from metallic to semiconducting, are being extensively investigated for use in device structures designed to control electron charge. However, another important degree of freedom--electron spin, the control of which underlies the operation of 'spintronic' devices--has been much less explored. This is probably due to the relative paucity of nanometre-scale ferromagnetic building blocks (in which electron spins are naturally aligned) from which spin-polarized electrons can be injected. Here we describe nanotubes of vanadium oxide (VO(x)), formed by controllable self-assembly, that are ferromagnetic at room temperature. The as-formed nanotubes are transformed from spin-frustrated semiconductors to ferromagnets by doping with either electrons or holes, potentially offering a route to spin control in nanotube-based heterostructures.     

Room-temperature ferro-magnetic semiconductor MnxGa1-xSb

Magnetic semiconductors can combine the semi- conducting properties with magnetic properties, and be used in these applications, such as magnetic field sensors, magnetic memory elements and, in long range, quantum computation and communication.Ⅱ-Ⅵ based diluted magnetic semiconductors (DMSs) have been extensively studied[1—3], because some magnetic ions are easily incor-porated into Ⅱ-Ⅵ compounds by substituting group Ⅱ atoms. It was conventionally considered that the equilib-rium solubi…     

Mn掺杂CuCrO2纳米粉体的室温铁磁性

利用固相反应与球磨相结合的方法,制备了(Cu_1-xMn_x)CrO₂ (0≤x≤6 at%) 和 Cu(Cr_1-yMn_y)O₂ (0≤y≤6 at%)两个系列的纳米粉体.结果表明,所有样品都具有3R-CuCrO₂铜铁矿单相结构.晶格膨胀说明Mn离子已分别固溶到(Cu_1-xMn_x)CrO₂的Cu亚晶格中和Cu(Cr_1-yMn_y)O₂的Cr亚晶格中,这在X射线光电子能谱的分析中得到了进一步的证实.B位Mn掺杂样品具有室温铁磁性,磁性源于Cr³⁺-Mn³⁺离子对间以空穴为媒介的双交换相互作用.CuMO₂(M=Cr,Mn)铜铁矿纳米粉体的饱和磁化强度比文献值高出约一个数量级,并随着Mn含量的增大而逐渐减小,主要受到3个因素的共同影响:M-M离子对数目、M-M离子间距及空穴浓度.     

河外水脉泽寄主星系的射电谱指数(英文)

详细调研并收集了所有河外水脉泽寄主星系的射电观测资料(84个源).在6 cm和20 cm两个波段,"千脉泽"(其光度小于10个太阳光度)源的射电流量都大于"兆脉泽"源(其光度大于10个太阳光度).由收集的这两个波段的观测数据,首次导出了水脉泽星系的射电谱指数,α=0.87±0.11.比较水脉泽星系和没有检测到水脉泽的星系的谱指数,没有发现明显的差异.进一步分析水脉泽各向同性辐射光度与脉泽寄主星系射电强度,发现它们之间存在一个强相关,这与水脉泽辐射可能是对背景射电连续谱的放大的理论结果相吻合.