钛酸钡基铁电材料的介电非线性研究

通过A位或B位掺杂改性得到的钛酸钡基铁电材料,在外加直流偏置电场作用下,具有介电常数非线性可调的优异介电性能,可以广泛地应用于压控可调陶瓷电容器和微波可调器件领域。针对钛酸钡基铁电材料的介电非线性特性,讨论了BaTiO_3基铁电材料分别在铁电相、顺电相以及相转变温度场附近的介电非线性机理和相关理论;结合笔者近年来有关介电非线性研究的实验结果和相关文献报道,综述了不同A位离子(如Sr~(2-)和Ca~(2-)等)或B位离子(如Zr~(4 )和Sn~(4-)等)掺杂的BaTiO_3基铁电材料体系的介电非线性研究现状,分别对不同物质形态(陶瓷块体、薄膜和厚膜)的BaTiO_3基铁电材料的介电非线性研究及其应用进行了对比分析;并对钛酸钡基铁电材料今后的发展趋势和研究方向进行了展望。     

正交相Ca_2Ge电子结构及介电极化特性的第一性原理研究（英文）

采用基于密度泛函理论的第一性原理超软贋势平面波方法计算了Ca_2Ge的电子结构、各方向的介电函数和极化对各方向的介电函数的影响。研究结果表明:Ca_2Ge是带隙值Eg=0.483 e V的直接带隙半导体,价带主要由Ca 3d和Ge 4p电子贡献,价带中存在s-p-d和p-d两种轨道杂化,导带主要由Ca 3d电子贡献,不存在杂化轨道。Ca_2Ge介电函数存在各项异性,当受到极化时,(100)和(001)方向的介电常数减小,虚部的第一介电峰呈现蓝移现象,最大介电峰增强,电子跃迁增加;(010)方向的介电常数增加,虚部第一介电峰呈现红移,最大介电峰增加。说明极化促进电子跃迁,是调控电子跃迁的有效手段,计算结果为的研究提供理论参考。     

A_2BO_4型类钙钛矿材料的第一性原理研究进展

介绍了A_2BO_4型类钙钛矿的结构和第一性原理方法,并从布居数、能带、态密度等方面,详细概括、分析了A_2BO_4型类钙钛矿材料电子结构、介电性质、光学性质和离子迁移率等性质的第一性原理方法计算的研究进展。     

A_2BO_4型类钙钛矿材料的第一性原理研究进展

介绍了A_2BO_4型类钙钛矿的结构和第一性原理方法,并从布居数、能带、态密度等方面,详细概括、分析了A_2BO_4型类钙钛矿材料电子结构、介电性质、光学性质和离子迁移率等性质的第一性原理方法计算的研究进展。     

掺杂对准同型相界附近PMN-PT陶瓷介电和铁电性能的影响

采用氧化物固相反应法制备了A、B位离子掺杂0．67Pb（Mg1/3Nb2/3）O3-0．33PbTiO3陶瓷,研究了掺杂对陶瓷的相结构、介电和铁电性能等的影响。Sm和La两种A位掺杂离子的引入,均较大幅度的降低了样品的介电常数峰温和声誉极化值,同时材料的最大介电常数也有了不同程度的降低。而随着B位离子Mn掺杂量的增加,使陶瓷样品中钙钛矿相逐渐增加,焦绿石相逐渐降低;而且部分掺杂的Mn离子会进入到晶格的B位,形成第二相;同时随着Mn离子掺杂量的增加,介电峰值逐渐增大,压电性能有所提高,弥散度依次增大。当锰掺杂量为1．5％mol时的压电陶瓷组分,其介电和压电性能各为：ε=2300,kp=0．54,Qm=900,tanδ=0．004,d33=400pC／N,适合于制作大功率压电陶瓷变压器。     

钼酸镉晶体电子结构和光学性质的第一性原理研究

本文利用了基于密度泛函理论的第一性原理和平面波赝势方法计算了CdMoO4晶体的电子结构和光学性质.分别采用了广义梯度近似(GGA)和局域密度近似(LDA)对晶胞参数进行优化,得到了最稳定状态下的晶胞参数.在优化结构的基础上得到了两种近似下的能带结构,电子态密度和介电函数.能带结构表明CdMoO4的价带顶和导带底均在Γ点,直接带隙分别为2.342 eV (GGA),2.241 eV (LDA).电子态密度计算结果说明Mo4d和O2p轨道之间强烈杂化形成Mo-O共价键,且其键性强于Cd-O键.计算得到的介电函数实部与虚部和Abraham等用WIEN97软件计算的结果吻合得较好.     

A2B′B″O6型双钙钛矿氧化物的研究进展

双钙钛矿氧化物具有A2B'B'O6结构通式,通常碱土金属离子占据A位,过渡金属或者镧系金属离子占据B位。由于B位离子(B'和B')的组合方式多样化,使得双钙钛矿结构氧化物拥有多种晶体畸变类型,呈现出丰富的强关联物理现象(如庞磁电阻效应、电子相分离、电荷/轨道有序等),这为人们研究电子强关联物理机制提供了一个良好的研究体系。综述了近年来双钙钛矿氧化物的研究进展:首先介绍晶体结构特征、制备方法及微结构表征技术,重点评述了其铁电、铁磁及多铁性方面的研究进展;其次讨论了它们在自旋电子学、铁电光伏及固体燃料电池领域的应用前景;最后指出了目前双钙钛矿氧化物研究需要重点关注的一些问题。     

BaO-Ln2O3-TiO2系高介电常数微波介质陶瓷的研究进展

简要叙述了BaO-Ln2O3-TiO2系微波介质陶瓷的结构研究情况,介绍了近年来该体系不同离子A、B位取代对微波介电性能的影响,最后提出了该材料需要进一步解决的问题和发展前景.     

Chelex 100吸附锶离子的理论计算

为探索Chelex 100树脂在微观结构吸附锶离子的作用机理,了解树脂的功能基团单分子在顶位和桥位,双分子在3种桥位与单个锶离子发生作用,以及双分子与2个锶离子的反应行为,采用量子力学分子动力学混合方法(hybrid QM/MM)研究Chelex 100树脂功能分子与锶离子反应的能量。计算7种吸附模型QM原子的电子结构参数,包括偶极距、最高占据轨道能量、最低非占据轨道能量、能隙、Fukui指数和Mulliken电荷布居。计算结果表明:锶离子在Chelex 100树脂分子桥位饱和吸附时相对稳定。     

PDVT单体的电子结构与红外光谱

有机共轭聚合物在电致发光材料上有较大的应用前景。采用密度泛函理论B3LYP方法在6-311++G(d,p)水平上计算了PDVT的分子结构和电子结构,并对红外光谱、净电荷布局等进行了分析,结合前线轨道理论探讨了分子的稳定性和活性。计算结果表明PDVT分子中环状结构的共轭效应良好,其中C(26)的反应活性最高,最容易接受亲电试剂的进攻。前线轨道分析表明PDVT分子的内部环状结构对HOMO轨道做主要贡献,S原子对LUMO轨道做主要贡献,计算所得△Eg=0.489eV表明它更倾向于接受电子并具有适合的能带宽度。PDVT分子具有较小的空穴重组能,空穴载流子速率大,可作为良好的空穴传输材料。     

生物活性多糖结构与功效关系的研究进展

生物活性多糖具有抗肿瘤、抗病毒、降血糖、降血脂等多种生物功能,其功能与结构密切相关。多糖结构与功能关系的研究已经成为人们关注的一个热点。本文综述了生物活性多糖的结构及其构效关系。     

阻尼结构对复合结构阻尼性能的影响

对比自由阻尼结构和约束阻尼结构的阻尼性能,研究基板、阻尼层、约束层对约束结构阻尼性能的影响。结果表明：约束结构阻尼性能相较于自由结构更好;约束阻尼结构中,基板越薄,阻尼层和约束层越厚,复合结构阻尼性能越优异。     

Structure of Spinel

This paper reviews the crystal structure of compounds with the general formula AB₂X₄, which crystallize with the same atomic structure as the mineral spinel, MgAl₂O₄. Three degrees of freedom associated with the detailed atomic arrangements of spinels are considered here: (i) the lattice parameter, a ; (ii) the anion parameter, u ; and (iii) the cation inversion parameter, i. Oxide spinels are used as examples to explore the interrelationships between these parameters.     

Structure of nanodiamonds

The structure of nanodiamonds is considered within the model of icosahedral nanoparticles with a local diamond-like order and a shell structure. The diffraction from nanoparticles with noncrystallographic (in particular, icosahedral) packings of atoms is analyzed. It is demonstrated that the method proposed for calculating the intensity of coherent scattering by clusters of identical polyatomic aggregates is applicable to the entire diversity of carbon structures existing in the nanoworld.     

离聚体的结构及其影响因素

离聚体中的离子对具有一定的配位结构,由于离子对的聚集作用能形成多重离子对或离子簇结构;离子对含量、离子对的特性、聚合物基质的性质、增塑剂、吸收的水份及热作用等都将影响离聚体的结构.本文对这些内容进行了综述.     

Band Structure Calculations of the High-Temperature Electronic Structure of Magnesium Oxide

The effects of high temperature on the electronic structure of a material consist of two major contributions, thermal lattice expansion and the electron-phonon interaction. These can produce dramatic changes in the electronic structure and play a critical role in the high-temperature properties and behavior of ceramics. We have used ab initio pseudofunction band structure methods to calculate the temperature dependence of the electronic structure of MgO from 300 to 1300 K modeling the independent effects of thermal lattice expansion and the electron-phonon interaction. The band structure calculations were performed self-consistently on a (MgO)₄ supercell using experimental values obtained from high-temperature X-ray diffraction to determine the lattice constants up to 1300 K and the root mean square amplitude of phonon displacements. Lattice thermal expansion contributed -0.15 meV/K to the band gap temperature dependence. Individual phonon modes, with displacements in the 〈111〉, 〈110〉, and 〈100〉 directions, were modeled using distorted lattice calculations. The electron-phonon coupling was found to be strongest for the 〈100〉 mode modeled, with strong coupling seen for modes which lead to the smallest decrease in the Mg-O bond length. The overall magnitude of the electron-phonon contribution to the band gap temperature dependence for the phonon modes modeled was −0.95 meV/K. The theoretical results account for a band gap temperature dependence in MgO of −1.1 meV/K, which compares well with the temperature dependence of approximately −1 meV/K determined experimentally using vacuum ultraviolet spectroscopy.     

应用“知识逻辑结构教学法”提高结构化学教学质量

论述了结构化学课程的特点和教学中的主要矛盾,总结了常规教学方法的局限性,找到了提高结构化学教学质量的有效途径:即采用"知识逻辑结构与思维形式注记教学法",制作并使用"知识逻辑结构呈现式"课件,并适当结合"启发式教学法"。     

胎体结构对塑料轮胎性能影响的仿真研究及结构优化

以有限元分析软件为平台,建立了不同胎体结构的塑料轮胎的三维有限元模型,得到了胎体等效应力和胎面接地应力分布以及轮胎径向刚度和横向刚度特性曲线,深入揭示了胎体结构对轮胎疲劳性能、耐磨性能、乘坐舒适性能和操控转向性能的影响。在此基础上提出了一种胎体结构优化方案,极大地改善了胎面应力分布,有效减小了胎面的不均匀磨损程度。     

Structure of polystyrene glasses

Wide-angle X-ray scattering from both unoriented and axially deformed glassy polystyrenes (atactic and quenched isotactic) is compared with that calculated for isolated molecules in different conformations. No satisfactory fit is obtained. It is apparent that the scattering beyond $\text{s=1.0}\text{A}\text{?}{}^{\mathrm{?1}}$ is very similar to that from benzene and styrene, having a large contribution from contacts between phenyl groups attached to neighbouring molecules which are not represented in a single chain model. The only significant difference between the scattering of the polymer and the two low molecular weight liquids is that there is a small peak at $\text{s=0.75}\text{A}\text{?}{}^{\mathrm{?1}}$ (0.62 Å^?1 for the isotactic glass) which forms on polymerization and was first reported by Katz in 1927. For drawn samples the peak intensifies on the equator and apparently represents interchain correlations. However, in comparison with those of other non-crystalline polymers this interchain peak is weak, at a surprisingly low scattering angle in relation to the expected spacing of the chains and shows a very significant increase in intensity with increasing temperature. A model is proposed in which the phenyl groups segregate on a molecular scale to form stacks; there are fewer stacks than chain backbones and they have a low electron density core which expands considerably in relation to its small diameter as the sample temperature increases. The model accounts for the position and temperature sensitivity of the interchain ‘polymerization’ peak. It also shows some similarities to the organization of isotactic molecules in the crystalline state. The stacks of phenyl groups contribute to the X-ray pattern as if they were flexible superchains. The cylindrical distribution function derived from the scattering pattern of the oriented polymer indicates that the phenyl groups are in register in all directions over distances of the order of several chain diameters.     

Film Structure and Adhesion

Paint films although attached to a substrate on one side only may be subjected to stresses, comparable to those in structural adhesives. These stresses result from shrinkage during film formation and subsequent ageing, mechanical strains, relative thermal movements of film and substrate and from osmotic pressure due to soluble material under or within the film. The adhesive strength required to prevent detachment varies from very little for weak, highly porous coatings to 10,000 lb/in² for tough coatings of high elastic modulus. Generally, adhesive strength both to the substrate and between coats in a paint system must exceed cohesive strength, under the conditions when failure is likely to develop. Dispersion and other forces, such as hydrogen bridging, between coatings and clean metal substrates should suffice to ensure adhesion but most practical surfaces carry contaminants, which interfere with wetting and intimacy of contact. Solvents and other low molecular weight components may also provide a weak interfacial layer, at least for a period after application. Modification of polymer structure to improve contaminant displacement and to increase polymer/substrate interaction forces, for example by the introduction of polar substituent or end groups will be discussed and potentialities of adhesion-promoting surface treatments reviewed.