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.     

Diffuse dielectric anomaly of （Na0.5K0.5Bi）0.5TiO3 crystal at high temperature

This paper investigates the dielectric properties of (Na_0.5K_0.5Bi)_0.5TiO₃ crystal at intermediate frequencies (1kHz \le f \le 1MHz) in the temperature range of 30--560℃. A pronounced high-temperature diffuse dielectric anomaly has been observed. This dielectric anomaly is shown to arise from a Debye-like dielectric dispersion that slows down following an Arrhenius law. The activation energy E_r obtained in the fitting process is about 0.69eV. It proposes that the dielectric peak measured at low frequency above 400℃ is not related to the phase transition but to a space-charge relaxation.     

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 trifluoroethylene monomers on molecular conformation of poly（vinylidene fluoride-trifluoroethylene） copolymer

Hartree－Fock and density functional theory (DFT) methods were employed to study poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] molecular chains with different VDF contents. The dependence of dipole moment of P(VDF-TrFE) chains on VDF content obtained from our calculation is in good agreement with the experiment. The TrFE monomer plays an important role in introducing the gauche bond into copolymer chains. A possible mechanism was interpreted.     

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：     

不同介孔材料固定青霉素酰化酶的稳定性研究

介孔材料由于具有在2～30nm之间可调的纳米级规则孔道、大比表面积和强吸附性能而成为固定化酶的优良载体．将酶固定于介孔材料的孔道中制备成的固定化酶与溶液酶相比,有易于与产物分离,并可回收和反复使用,可降低生产成本,减少酶的自水解和保持酶的活性．青霉素酰化酶（Penicillin acylase,PGA,EC．3．5．1．11）又称为青霉素酰胺酶或青霉素氨基水解酶,该酶属于球蛋白,分子量较大,由2个亚基组成：分子量为19500的含有侧链结合位点的亚基和分子量为60000的含有催化位点的亚基．     

三维无机-有机杂化骨架微孔材料Zn_3(bpdc)_3(4,4′bpy)·DMF·2H_2O的合成与结构

合成了一个具有三维骨架结构的无机 -有机杂化微孔材料Zn3(bpdc)3(4,4′ bpy)·DMF·2H2 O,并通过ICP和X射线单晶衍射分析等手段对其结构进行了表征.晶体属于正交晶系,Pbcn空间群,晶胞参数a =1.45 3 2 (3)nm,b =2.5 0 3 7(5 )nm,c=1.8184(4)nm,V =6.616(2 )nm3,Z =8,Dc=1.2 96g/cm3,Mr=64 5.5 8,μ =1.145mm-1,F(0 0 0)=2 65 6.最后的一致性因子为R =0.0 70 5,Rw =0.2 0 5 6.     

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.     

CaCu3Ti4O12陶瓷的微观结构和电学性能

利用传统的固相反应工艺,在不同的烧结温度下制备了一系列的CaCu3Ti4O12陶瓷样品,考察了其微观结构以及介电和复阻抗方面的电学性质.研究发现这些样品在微观结构方面可分为三种类型,高介电性与微观结构有着密切的关联性.室温下,样品的低频介电常数随陶瓷晶粒尺寸的增大而提高.随着测试温度的升高,不同微观结构类型的样品呈现出不同的电学性质的变化,但其中也存在着一些相同的特征.高温下,介电频谱呈现出一个低频介电响应和两个类Debye型弛豫色散,复阻抗谱呈现出三个Cole-Cole半圆弧.将实验上观测到的电学性质的起因归于陶瓷多晶微结构中的晶畴、晶界和晶粒内的缺陷.     

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