Nb掺杂对还原性烧结的TiO2-δ陶瓷的晶体结构及热电性能的影响

利用传统的固相反应法在还原性气氛1200 ℃下分别制备出不同Nb掺杂量的Ti_1-xNb_xO_2-δ陶瓷样品.样品的粉末X射线衍射(XRD)结果显示:Nb掺杂量x较低时样品为多相混合,当Nb掺杂量x>0.02时样品为单一的四方相金红石型结构.在室温到900 K的测试温区,测试了单相样品(x=0.02,0.03,0.04)的电导率、Seebeck系数和热导率.测试 关键词： 氧化钛陶瓷 热电性能 氧空位     

基于拉普拉斯方程的任意形状热斗篷研究与设计

如何灵活地控制和操纵热流是目前研究的热点.本文基于拉普拉斯方程提出了一种设计任意形状热斗篷的方法.对于形状规则的热斗篷,在特定边界条件下求解拉普拉斯方程得到了斗篷区域材料的热导率分布解析表达式;对于不规则形状的热斗篷,通过数值求解拉普拉斯方程得到了斗篷区域材料的热导率参数分布.全波仿真结果表明,所设计的二维和三维任意形状热斗篷内部隐身区域的热通量为零,从而具有热保护功能;同时,热流绕过斗篷后温度场恢复原来的分布,实现了完美隐身功能.这项研究为解决热斗篷内外边界非共形问题提供了一种可行的方法,对热保护器件的设计和制备有指导意义.     

聚氨酯制备的多尺度模拟方案

针对聚氨酯材料特性设计了多尺度计算机模拟方案, 并研究了不同原料及相同原料但不同官能度对所制备的聚氨酯材料力学性能和玻璃化转变温度的影响. 基于原子级别的结构, 建立了耦合聚合反应的粗粒化耗散粒子动力学模型来描述组分扩散及交联网络结构的形成过程. 并反映射这个粗粒化结构到全原子级别来分析材料的力学性能和热力学性能. 这个多尺度研究方案也可推广到研究多个竞争性因素同时主导的复杂体系中.     

Scheme for Generation of Maximally Entangled States via Entanglement Swapping

Based on two atoms and two cavities initially in two pairs of atom-photon nonmaximally entangled states, we propose a relatively simple scheme to create maximally entangled photon-photon and atom-photon states via entanglement swapping using techniques of cavity QED inspired by the scheme proposed in [Phys. Rev. A 71 （2005） 044302] and [Phys. Rev. A 71 （2005） 034312]. Our scheme does not involve the measurement in Bell basis, we only require detecting the states of atoms.     

一维金属光栅的透射光学特性

利用时域有限差分法模拟了一维金属光栅的透射光场的分布及光栅厚度等因素对透射光谱的影响.结果表明:特定波长的光通过金属光栅中的亚波长狭缝时有异常大的透过率增强.分析其物理起源,认为是类FabryPerot(FP)腔作用的结果.基底介电常量对类FP腔长度的调制导致了对透射光谱的影响.金属光栅表面激发的表面等离子体激元波与多缝干涉一样,对透射光谱有一定的影响,但不是形成增强的原因 关键词： 金属光栅 透射光学特性     

First-Principles Calculations of Elastic Properties of Cubic Ni2MnGa

Dependence of bulk modulus on both pressure and temperature, the elastic constants Cij and the pressure and temperature dependence of normalized volume V/Vo of cubic Ni2MnGa alloy are successfully obtained using the first-principles plane-wave pseudopotential （PW-PP） method as well as the quasi-harmonic Debye model. We analyse the relationship between bulk modulus and temperature up to 800 K and obtain the relationships between bulk modulus B and pressures at different temperatures. It is found that the bulk modulus B increases monotonically with increasing pressure. Moreover, the temperature dependences of the Debye temperature are also analysed. The calculated results are in agreement with the available experimental data and the previous theoreticM results.     

Existence and multiplicity for solutions of Neumann problem for semilinear elliptic equations

The existence and multiplicity results are obtained for solutions of Neumann problem for semilinear elliptic equations by the least action principle and the minimax methods respectively.     

溶胶-凝胶法制备Bi0.5Na0.5TiO3陶瓷及其电学特性

用溶胶-凝胶工艺成功制备出Bi05Na05TiO3纳米微粉，并利用此微粉烧结出高致密度的Bi05Na05TiO3陶瓷.这种新工艺制备的Bi05Na05TiO3陶瓷，其压电性能远远高于普通方法制备的陶瓷，其中压电常数d33和机电耦合系数kt分别高达102×10-12C/N和58%.同时发现，对于这种Bi05Na05TiO3陶瓷，室温时只需施加100kV/cm左右的交变电场，就可得到矩形度极好的饱和回线，得到的剩余极化Pr和矫顽场Ec分别为32μC/cm2和61kV/cm.而在100℃以上只需施加35kV/cm的极化电场就可使样品充分极化.     

Cu Doping Effect on Electrical Resistivity and Seebeck Coefficient of Perovskite-Type LaFeO3 Ceramics

Perovskite-type LaFe_1-xCu_xO₃ (x=0.10$, 0.14, 0.18) solid solution is prepared with the conventional solid-state reaction technique. The electrical resistivity and the Seebeck coefficient are measured in the temperature range 473-1073K to elucidate the Cu doping effect on the thermoelectric properties of the LaFeO₃. The electrical resisitivity of LaFe_1-xCu_xO₃ shows semiconducting behavior. The temperature dependence of the electrical resistivity indicates that the adiabatic small-polaron hopping mechanism is dominant for their electric transportations. The activation energy decreases with the increasing Cu content as well as the increasing temperature. The Seebeck coefficient changes from a negative value to a positive value around 510K, and increases with rising temperature up to 710K, then becomes saturated around 200μV/K. The Seebeck coefficient decreases with the substitution of Cu atoms in the temperature range of 573-1073K, while the electrical resistivity decreases with the substitution of Cu atoms in the whole measured temperature. Overall the power factor increases with rising temperature, and the highest value of power factor is 54μW/K²m for x=0.10 of Cu doping.     

Ca_3NbGa_3Si_2O_(14)晶体的介电和压电特性

利用Y切和 (yxl) 30°切两种样品测量了Ca3NbGa3Si2 O1 4晶体的介电、压电和部分弹性参数 .计算了 (yxl)θ切型相关压电常数随切角的变化 .与La3Ga5SiO1 4晶体相比 ,Ca3NbGa3Si2 O1 4晶体具有更优良的压电性能 ,其压电常数d1 1=7 93× 10 - 1 2 C N ,d1 4=- 5 88× 10 - 1 2 C N .