零声表面波频率温度系数方向的硅酸镓镧晶体生长

采用提拉法生长了高质量、大尺寸、结构完整的声表面波零温度系数切向LGS晶体.XRD图谱显示,生长的晶体为单一相LGS晶体,晶格常数为a=0.816274 nm,c=0.509253 nm,密度为5.7463 g/cm3.压电常数、介电常数、热膨胀性能等与传统方向生长的晶体一致.用此方向生长的LGS晶体制作声表面波频率温度性能优化的切片,只需要垂直生长方向进行切割,可以大大简化晶体的加工工艺、提高LGS晶体的利用率,节省材料成本.     

碳纳米材料及其在多相催化中的应用

碳纳米材料（包括零维、一维、二维碳纳米材料以及碳纳米孔材料）是一类新型的催化剂或催化剂载体材料,在氧化脱氢、选择加氢、合成氨、氨分解制氢以及燃料电池等多相催化领域具有广阔的应用前景。本文综述了近年来新型碳纳米材料在多相催化领域中的应用研究进展,介绍了这类催化材料的制备方法,重点阐述了碳载体的微/介观结构、掺杂、电子性质、表面性质、限域效应等对所担载的催化活性组分的分散,对反应物的扩散以及对催化反应的活性和选择性等方面的影响。     

Thermoelectric properties of Li-doped Sr_(0.7)Ba_(0.3)Nb_2O_(6-δ) ceramics

Thermoelectric properties of Li-dopedSr_(0.7)Ba_(0.3)Nb_2O_(6-δ)ceramics were investigated in the temperature range from 323 K to 1073 K. The electrical conductivity increases significantly after lithium interstitial doping. However, both of the magnitudes of Seebeck coefficient and electrical conductivity vary non-monotonically but synchronously with the doping contents, indicating that doped lithium ions may not be fully ionized and oxygen vacancy may also contribute to carriers. The lattice thermal conductivity increases firstly and then decreases as the doping content increases, which is affected by competing factors.Thermoelectric performance is enhanced by lithium interstitial doping due to the increase of the power factor and the thermoelectric figure of merit reaches maximum value(0.21 at 1073 K) in the sample Sr_(0.70)Ba_(0.30)Li_(0.10)Nb_2O_6.     

Structure and dynamics of ordered water in a thick nanofilm on ionic surfaces

The structure and dynamics of water in a thick film on an ionic surface are studied by molecular dynamic simulations. We find that there is a dense monolayer of water molecules in the vicinity of the surface. Water molecules within this layer not only show an upright hydrogen-down orientation, but also an upright hydrogen-up orientation. Thus, water molecules in this layer can form hydrogen bonds with water molecules in the next layer. Therefore, the two-dimensional hydrogen bond network of the first layer is disrupted, mainly due to the O atoms in this layer, which are affected by the next layer and are unstable. Moreover, these water molecules exhibit delayed dynamic behavior with relatively long residence time compared with those bulk-like molecules in the other layers. Our study should be helpful to further understand the influence of water film thickness on the interfacial water at the solid-liquid interface.     

云南私营企业现状及其问题研究

改革开放以来,中国的私营经济经历了从无到有以至逐渐壮大的发展过程。通过对相关数据的整理、分析,将私营企业在云南国民经济中的地位和贡献予以量化,不难发现,私营企业在国民经济中占有重要甚至支柱性质的地位,两者的发展相辅相成。     

光折变晶体KTa0.5Nb0.5O3光学特性的第一性原理研究

用全电势线性缀加平面波法(FLAPW)计算了KTa0.5Nb0.5O3四方相和立方相 的光学特性，即介电函数虚部ε２(ω)、光学吸收系数I(ω)和反射率R(ω). 在四方相，介电虚部沿a，b轴，在3，7和23eV附近，分别有三个介电峰.沿c轴的三个介电峰分别位于4，8和23eV.其中4eV附近的介电峰非常尖锐而且高.从8至18eV，沿a，b ，c轴三个方向都有许多低的介电峰.通过对两相光学特性的对比分析发现铁电相KTa0.5Nb0.5O3具有更强的各向异性. 关键词： 平面波法计算 光学常量和参数 铁电体     

氢键铁电体相变的格林函数理论(Ⅱ)

在文献[1]的基础上,计算了包括四体相互作用项的氢键铁电系统自由能,给出了确定铁电一级相变时序参数跃变和居里温度的表示式。通过对自由能在相变温度附近行为的详细分析,表明了微观理论结果与朗道热力学理论完全一致,并给出了朗道自由能表示式中各系数与微观相互作用参数之间的关系,使各系数的物理意义更加明确。再通过与PbHPO₄,PbDPO₄和H₂C₄O₄等晶体的实验结果比较,进一步证明本文理论能成功地处理氢键铁电体的一级相变和二级相变问题。 关键词：     

Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3

We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.     

Effect of Vibration on Water Transport through Carbon Nanotubes

We study the response of water permeation properties through a carbon nanotube on the time-dependent mechanical signals. It is found that there is a critical frequency of vibrating fc （about 1333 GHz） which plays a significant role in the water permeation properties. The total water flow, the net flux, the number of hydrogen bonds and the dipole flipping frequency of the single-file water chain inside the nanotube are almost unchanged for the frequency of vibrating f 〈 fc. Simulation results show that the nanotube can be effectively resistant to the mechanical noise. Such excellent effect of noise screening is attributed to the exceptional property of water molecules connected by strong hydrogen bonds with each other and forming a one-dimensional water chain inside the nanotube. Our findings are important for the understanding of why biological systems can achieve accurate information transfer in an environment full of fluctuations.     

平面双核酞菁化合物的发展及应用前景

主要阐述了平面共享一个苯环的双核酞菁的合成、性质及应用,简单介绍了双核酞菁的发展和两种基本合成方法,并详细介绍了该类化合物的催化、氧化还原、荧光、LB膜、液晶性质,同时对其应用前景进行了展望。