An electrochemomechanical theory of defects in ionic solids. I. Theory

Charged defects diffuse through an ionic solid under electrochemical driving forces. Such a diffusion process can be affected by mechanical stresses in the solid. A deviation of defect concentration from its stoichiometric value during diffusion can cause volumetric strains in the solid. Such strains will result in mechanical stresses if the ionic solid is under mechanical constraint, or if the defect distribution is non-uniform. We develop a framework to account for the coupling between mechanical stresses and diffusion of charged defects in ionic solids. The framework consists of a system of nonlinear differential/algebraic equations governing the defect concentrations, electrostatic potential and the mechanical stresses. It is believed that this framework is the first fully coupled theory for the interaction between mechanical stresses and electrochemical forces in ionic solids.     

双差分霍尔法微位移测定金属线胀系数

金属线胀系数是金属的重要性能参数,精密测定其线胀系数在机械制造方面意义重大.本论文采用4个线性霍尔元件和3个仪表放大器构成双差分微位移传感器,采用该传感器测定金属的线胀系数.实验结果表明该传感器灵敏度高,线性度好,测量误差在±0.4％.     

钨/石墨烯/钨面向等离子体复合材料力学与热学及耐辐照性能衰减的第一性原理计算

通过第一性原理计算研究了钨/石墨烯/钨复合材料相比于纯钨金属在力学与热学性质方面的变化,并用氦原子-空位缔合缺陷模拟核聚变辐照损伤评估等离子体辐照条件下的性能。计算结果表明：钨/石墨烯/钨复合材料的体积弹性模量、杨氏模量与剪切模量呈现一定程度的下降,但是提升了钨基材料的延展性;钨/石墨烯/钨复合材料的热膨胀系数有所增加,但是具有较高的最小热导率。本文阐述了石墨烯界面层可以对基体杂质与缺陷进行吸附的独特机制,通过这种机制,钨/石墨烯/钨复合材料在力学、热膨胀系数以及最小热导率有更低程度的衰减,这显示了钨/石墨烯/钨复合材料在抗辐照性能方面具有较大的应用潜力。     

Invar and covar behavior of simple ferromagnets: Thermodynamic simulation

Thermodynamic model calculations are performed with the aim to show that the invar behavior of a ferromagnet (when its thermal expansion coefficient is close to zero in a climatic temperature range) results from a certain optimum relation between the thermodynamic parameters characterizing the ferromagnetic state. The same is true for the covar behavior of a ferromagnet, when its thermal expansion coefficient is nonzero and almost constant in a certain temperature range. As a first approximation, calculations for simple ferromagnets are performed in terms of the thermodynamic Landau model.     

带缺陷二维光子晶体的透射谱研究

在一维线缺陷的研究基础上进一步应用转移矩阵方法数值研究带其它缺陷的二维正方晶格圆柱光子晶体的透射谱,缺陷的引入使得原来不透电磁波的禁带中,出现了缺陷模,即某一波长的电磁波可以透过,计算结果表明禁带位置、宽度,缺陷模的位置与透过率随着缺陷的种类、介质、程度有关,特别是都受到波源的入射角调制.     

光学系统实现热补偿的通用条件

运用光学系统的近轴成像公式，推导出微分形式的物面位于任意位置时热补偿的通用条件，包括薄单透镜、密接薄透镜组和分离薄透镜组等不同情况。推导过程中假设物面位置不随温度发生变化，并且忽略分离薄透镜组中各组分上光线入射高度随温度的变化。利用推导的条件建立了像距的归一化温度变化率与各透镜光热膨胀系数之间的关系，指出所得到的条件具有更加普遍的意义，能够指导机械和伺服控制系统的工程设计，并且在物面位于无穷远时与目前普遍采用的热补偿条件相吻合，即光学系统的光热膨胀系数等于壳体的热膨胀系数。     

The influence of particle distribution and interphase on the thermal expansion coefficient of particulate composites by the use of a new model

In this work, the thermal expansion coefficient (CTE) of a composite containing spherical particles surrounded by an inhomogeneous interphase embedded in an isotropic matrix is evaluated by means of a new model. The thermomechanical properties of the interphase are formulated as continuous radial functions. It is assumed that this third phase developed between the polymeric matrix and the filler particles contains both areas of absorption interaction in polymer surface layers onto filler particles as well as areas of mechanical imperfections. It can be said that the concept of boundary interphase is a useful tool to describe quantitatively the adhesion efficiency between matrix and particles and that there is an effect of this phase on the thermomechanical properties of the composite. The thickness and volume fraction of this phase were determined from heat capacity measurements for various filler contents. On the other hand, it is assumed that the particle arrangement (distribution) which can be considered as an influence of neighboring inclusions and their interaction should affect the thermomechanical constants of the composite. The theoretical predictions were compared with experimental results as well as with theoretical values from expressions obtained from other workers and they were found to be in satisfactory agreement.     

The effect of temperature,defect and strain rate on the mechanical property of multi-layer graphene: Coarse-grained molecular dynamics study

In this work, we investigate the effect of temperature, defect, and strain rate on the mechanical properties of multi-layer graphene using coarse-grained molecular dynamics (CGMD) simulations. The simulation results reveal that the mechanical properties of multi-layer graphene tend to be less sensitive to temperature as the layer increases, but they are sensitive to the distribution and coverage of Stone-Wales (SW) defects. For the same number of defect, there is less decline in the fracture stress and Young's modulus of graphene when the defects have a regular distribution, in contrast to random distribution. In addition, Young's modulus is less influenced by temperature and defect, compared to fracture stress. Both the fracture stress and Young's modulus have little dependence on strain rate.     

分子动力学研究表面缺陷对硅纳米线杨氏模量的影响

硅纳米线因受量子尺寸效应与表面效应的影响而具有奇特的力、电及其耦合特性,成为了纳米电子器件的核心构件.然而在硅纳米线的制备过程中,表面产生缺陷不可避免.因此本文采用分子动力学方法着重研究了表面缺陷浓度对不同横截面形状(正方形、六角形和三角形)的[110]晶向和[111]晶向硅纳米线杨氏模量的影响.研究结果表明,当硅纳米线仅有单一表面缺陷时,不同晶向硅纳米线的杨氏模量均随表面缺陷浓度增加而迅速单调减小.当表面缺陷浓度为10%时,杨氏模量的减小幅度在10%-20%之间,减小幅度的差异与硅纳米线的晶向以及横截面形状密切相关.当存在多个表面缺陷时,杨氏模量随着缺陷浓度的增加表现出了不同程度的波动趋势.三角形截面硅纳米线的杨氏模量波动幅度最大,正方形截面的波动较小,即表面缺陷分布的不同对正方形截面硅纳米线的杨氏模量影响较小,这表明表面缺陷的影响与其分布及硅纳米线的横截面形状密切相关.通过与实验结果对比,本文的研究结果揭示了表面缺陷是导致硅纳米线杨氏模量实验值变小的重要因素,因此在表征硅纳米线的力学性能时,需要考虑表面缺陷的影响.     

光子晶体局域缺陷模及耦合特性研究

用超胞平面波展开法计算了二维正方格子介质柱光子晶体缺陷模,系统模拟了在改变缺陷模数目和缺陷模之间的距离及在不同耦合方向等情况下的耦合特性。计算结果表明：局域缺陷模之间的耦合所产生分裂的缺陷模式频率随着缺陷之间的距离而发生变化．当缺陷之间距离增加时,缺陷模之间耦合变得越来越弱且奇模和偶模交替变化;随着耦合缺陷点数目增加,缺陷模在光子带隙内形成一个缺陷带;当平面波平行于缺陷模耦合方向入射时．可以同时激发奇模和偶模．当入射平面波垂直于耦合方向时．仅产生偶模;沿对角线方向耦合的定域化的缺陷模电磁场快速衰减使得那些方向每一个单谐振腔局域光场与它邻近的谐振腔不发生耦合,其本征频率与波矢无关。     

一维负磁导率材料中的缺陷效应

理论和实验已经表明，金属开口谐振环（split ring resonators,简称SRR）可以实现材料的有效磁导率μeff在某一频率范围内为负.采用波导法实验研究了不同几何尺寸的六边形SRR在X波段微波作用下的近邻相互作用.实验发现，相同尺寸的六边形SRR周期性排列而成的一维负磁导率材料存在一个谐振频率；当缺陷谐振环引入一维负磁导率材料时，主谐振频率和缺陷环谐振频率同时发生移动；主谐振频率和缺陷环谐振频率的移动量随缺陷与双环谐振频率之差的增加而减小，当缺陷环谐振频率与双环谐振频率接近时，环间的相互作用增强，频率的移动量增大. 关键词： 负磁导率 缺陷效应 开口谐振环     

二维成分无序颗粒体系中法向力的分布

运用离散元法研究成分无序体系中法向力的几率分布,该体系由两种不同刚度系数的颗粒规则堆积而成, 体系的无序程度由缺陷率控制.模拟发现,无缺陷时体系的力网几乎是均匀的,而有缺陷时力网变得不均匀. 提出了主法向力与次法向力的概念,并对它们分别进行统计;随着缺陷率的增加,主法向力的分布经历了比较复杂的变化过程,而次法向力总是指数型分布.模拟结果表明,缺陷率较小时成分无序体系中的法向力分布与随机堆积体系很不相同,而缺陷率较大时得到了与随机堆积类似的结果.这些结果有助于理解力网的不均匀性与体系无序性的关系.     

The reflection of the fundamental torsional mode from cracks and notches in pipes

A quantitative study of the reflection of the T(0,1) mode from defects in pipes in the frequency range 10-300 kHz has been carried out, finite element predictions being validated by experiments on selected cases. Both cracklike defects with zero axial extent and notches with varying axial extents have been considered. The results show that the reflection coefficient from axisymmetric cracks increases monotonically with depth at all frequencies and increases with frequency at any given depth. In the frequency range of interest there is no mode conversion at axisymmetric defects. With nonaxisymmetric cracks, the reflection coefficient is a roughly linear function of the circumferential extent of the defect at relatively high frequencies, the reflection coefficient at low circumferential extents falling below the linear prediction at lower frequencies. With nonaxisymmetric defects, mode conversion to the F(1,2) mode is generally seen, and at lower frequencies the F(1,3) mode is also produced. The depth and circumferential extent are the parameters controlling the reflection from cracks; when notches having finite axial extent, rather than cracks, are considered, interference between the reflections from the start and the end of the notch causes a periodic variation of the reflection coefficient as a function of the axial extent of the notch. The results have been explained in terms of the wave-number-defect size product, ka. Low frequency scattering behavior is seen when ka < 0.1, high frequency scattering characteristics being seen when ka > 1.     

Calculation of thermal stresses in profiled single crystals taking into account the temperature dependence of thermal expansion

Approximate expressions for stress tensor components in cylindrical and ribbon crystals are obtained taking into account the temperature dependence of the thermal expansion coefficient. These expressions are used for estimating the effect of the thermal expansion nonlinearity factor on the stress level. It is shown that the stresses emerging in linear temperature fields due to this factor are comparable with critical stresses for defect formation.     

石墨烯低温热膨胀和声子弛豫时间随温度的变化规律

考虑到原子非简谐振动和电子-声子相互作用,用固体物理理论和方法研究了石墨烯格林艾森参量和低温热膨胀系数以及声子弛豫时间随温度的变化规律,探讨了原子非简谐振动项对它们的影响.结果表明:1)在低于室温的温度范围内,石墨烯的热膨胀系数为负值,随着温度的升高,其热膨胀系数的绝对值单调增加,室温热膨胀系数为-3.64×10~(-6)K~(-1);2)简谐近似下的格林艾森参量为零.考虑到非简谐项后,格林艾森参量在1.40-1.42之间并随温度升高而缓慢增大,几乎成线性关系,第二非简谐项对格林艾森参量的影响小于第一非简谐项;3)石墨烯声子弛豫时间随着温度的升高而减小,其中,温度很低(T10 K)时变化很快,此后变化很慢,当温度不太低(T300 K)时,声子弛豫时间与温度几乎成反比关系.     

Self diffusion in nonstoichiometric compounds2

A formalism for tracer diffusion in nonstoichiometric compounds is developed at the Bragg-Williams approximation along parallel lines with the Anderson theory of nonstoichiometry. It is specifically assumed that both components of a Frenkel pair may contribute independently to the diffusion coefficient. The equation for the tracer diffusion coefficient leads to a “transition” region in a In D¹ vs $\text{1}\text{T}$ plot for one side of stoichiometry. In this region the slope may attain the value of the sum of the high and low temperature branches. It is also shown that under certain conditions the compositional behavior of the activation energy of diffusion should parallel the compositional behavior of the heat of solution. The success of the mass action law approach, as manifested in ln D¹/ln po₂ plots in the case of nonstoichiometric oxides, is also shown to be due to a self cancellation of terms involving defect interactions.     

低热应力热稳定曲线型阵列波导光栅复用器

相对方形阵列波导光栅波分复用器芯片而言,采用曲线切割的复用器芯片可以成倍地增加单个晶圆上的复用器产出率,但是曲线切割复用器的中心波长更加容易受到热应力的影响,该热应力是由于封装盒与耦合到复用器芯片上的带状光纤之间的线膨胀系数差异所引起的.本文实验分析了封装热应力对复用器中心波长的影响,结果表明,封装热应力与复用器中心波长之间的变化成线性关系.即使采用比较软的硅橡胶将复用器上的带状光纤固定到封装盒上,对于热稳定封装的曲线复用器而言,当环境温度在-20~65℃之间变化时,其中心波长也会有46 pm的变化.通过在热稳定复用器封装用的加热片上贴一片高硼硅玻璃,同时将带状光纤用硅橡胶固定到高硼硅玻璃上的方法,既保证了带状光纤相对封装盒固定,又减小了它们之间线膨胀系数不一致导致的热应力.实验结果表明,在-20到65 ℃温度范围内,这种复用器模块的中心波长高低温变化典型值小于5 pm,而且光纤所受的应力典型值小于0.029 MPa.     

Reflection coefficient of low-energy ions as a universal function of the scaled transport cross section

Multiple collision theory of heavy ion ranges in an infinite medium has been used to calculate the reflection coefficient from the penetration profile, by a method first described by Bottiger et al. Interaction with target electrons has been neglected and nuclear collisions have been described by the power cross sections. Calculations are restricted to low reduced ion energies )₀А.1 and to target/ion mass ratios 7⢪, when electronic stopping is much less than the nuclear stopping. The Gaussian approximation of the penetration profile and the reflection coefficient are found in a form of simple analytic formulas. Furthermore, the penetration profile was constructed by using Edgeworth expansion and moments of the distribution up to the fourth order, and the reflection coefficient was determined from the profile. Good agreement between the analytical results and the reflection coefficient obtained from Edgeworth expansion was found, for target atom/ion mass ratios 7̿.3. It is shown that the reflection coefficient is a universal function of the scaled transport cross section. The scaling is fulfilled for v̀, when ion reflection is determined by large-angle multiple collisions, and breaks down for v<1 i.e. 7<1, when scattering angles are small. Results are compared with TRIM computer simulation data.     

Bi1.7Pb0.3Sr2Ca2Cu3Ox超导体中晶体结构和电子性能与两个结构块的关联

用变温X－射线衍射,扫描量热分析,热重分析对精心制作的Bi1.7Pb0.3Sr2Ca2Cu3Ox超导样品在后处一前和后处理后从液氮温度到熔点温度进行了分析,并对样品进行了XPS分析,载流子浓度和超导电性测量。实验发现,样品沿C方向的膨胀系数在低温区有两个反常,在高温区有两个热量和重量反常。结果分析表明,这两个反常与晶体结构中两个不同的结构块有关,即钙钛矿和盐岩结构块。实验发现,这两上结构块之间的失配,超导临界湿度,样品中的氧含量,以及膨胀系数的变化之间有密切的关联。实验结果表明,了解两个不同结构块之间的相互作用对认识高温超导电性有重要作用。     

透明光学材料中缺陷吸收激光能量引起的热应力与断裂

 利用热弹性理论分析了在光学材料中由于缺陷吸收激光能量引起的温度和热应力分布，并且针对一个简单的裂纹模型分析了热应力产生的应力强度因子，并且给出了一些主要参数对于应力强度因子的影响的规律。