C12H9SN晶体铁弹相变的研究

采用慢度曲面法研究C12H9SN晶体的铁弹相变.在现有实验数据的基础上,模拟计算C 12 H9 SN晶体高温正交相的弹性劲度系数对慢度曲面的影响.结果表明,非对角元c12,c13,c23的变化对慢度曲面最大值的取向没有影响,同时也确定出与该相变直接相关的弹性劲度系数为c55.该晶体相变的对称性变化是由高温正交相mmm点群变成低温单斜相2/m点群.     

点群空间群生成元生成所有群元的一种算法

本文给出了一种由生成元计算所有群元的计算方法,该算法可用于点群、空间群及其一般群的计算.以Oh点群和空间群I23的生成元计算了它们的全部群元,结果证明该方法具有很高的计算效率.     

CsLiB6O10晶体及熔体微结构的高温拉曼光谱研究

本文利用高温原位拉曼光谱技术,测定了非线性光学晶体硼酸铯锂(CsLiB6O10,CLBO)晶体及其熔体的变温拉曼光谱.利用密度泛函理论计算了基本单元为(B3O7)5-六元环的CLBO晶体的拉曼光谱,并对振动模式进行了分析归属.在升温过程中,CLBO晶体的拉曼光谱出现展宽和红移,无相变发生;在熔化过程中,CLBO晶体微结构中(B3O7)5-六元环的[BO4]四面体发生异构化反应,转变为[BO3]三角形,即晶体相中的(B3O7)5-环变为熔体中的(B3O6)3-环.利用量子化学从头计算方法计算分析了熔体中结构基元的拉曼光谱谱学特征,结合熔体实测结果,表明CLBO熔体的阴离子基元为四个(B3O6)3-六元环组成的大四元环超级结构.     

3m点群晶体纵向压电性能的研究

本文详细地介绍了通过坐标变换研究晶体压电性能随空间变化的方法.在以前的工作基础上,对LiNbO3、LiTaO3和PZT60/40等3m点群晶体纵向压电系数d33及机电耦合系数k33在空间分布的共同规律进行了归纳总结,发现它们在空间中的分布具有明显的各向异性,并存在着一些特殊方向,沿这些方向,晶体的压电性能有较大幅度的提高.在此基础上,本文还根据不同文献中报道,对另一著名的3m点群晶体β-BaB2O4的压电系数数据进行了比较和分析.     

硼酸锶钡(Ba0.87Sr3.13B14O25)晶体的生长、结构和性质研究

本文报道了一种新的硼酸盐化合物-Ba0.87Sr3.13B14O25,采用泡生法已生长出尺寸为35mm×25mm×5mm的晶体.该晶体为单斜晶系,C2/m空间群,a=1.6425(3)nr,b=0.77739(16)nm,c=1.6665(3)nm,β=119.22(3)°,Z=4.结构中B3O8六元环通过O原子和BO3三角形相互连接,构成三维的硼氧阴离子骨架,金属阳离子占据多面体间的空隙.测量了BSBO晶体的透过谱,该晶体的显微硬度为578kg/mm2.     

层状化合物La0.26Bi0.74OOH光学性能的研究

构建非中心对称结构及研究材料的构效关系对于探索新型非线性光学晶体具有重要意义.La0.26Bi0.74OOH是一种具有PbFC1型结构的层状化合物,结晶在非中心对称的正交晶系空间群Pmm2,其主体结构由[La0.26Bi0.74O2]-层和H+阳离子组成.本文采用水热法合成了La0.26Bi0.74OOH晶体,并首次测试了该化合物的非线性光学性能.粉末倍频实验显示La0.26Bi0.74 OOH的倍频响应为KH2PO4的0.6倍.紫外-可见-近红外漫反射光谱表明该化合物的截止波长为335 nm.此外,第一性原理计算显示该化合物为直接带隙半导体,其内部的Bi-O和La-O基团对La0.26Bi0.74 OOH的非线性光学性能起主要作用.     

流固耦合二维声子晶体的数值模拟和实验研究

为了研究流固耦合声子晶体的特性,本文应用有限元方法进行数值模拟并通过实验进行了验证.以二维钢柱/水正方晶格声子晶体为研究对象,利用ABAQUS有限元软件计算得到了完好周期和线缺陷情况下的传输谱和声压分布.同时利用脉冲响应技术进行实验测量,得到了以上两种情况下的带隙范围.结果表明,两种方法结果吻合得很好,说明有限元方法在计算流固耦合声子晶体问题上的优越性.     

AgGa0.7In0.3Se2晶体热膨胀行为研究

采用一种新的定向方法,快速定出了AgGa0.7In03Se2晶体c轴方向,制备得到[001]、[100]方向的块状样品;采用德国B(a)hr公司的WinTA 100热膨胀仪对其进行测试,分别获得了晶体沿c轴、a轴方向的热膨胀系数,分析了它们随温度变化的规律以及晶体出现反常热膨胀的机制;计算出晶体的体热膨胀系数和各向异性因子,分析讨论了晶体非轴向热膨胀系数在不同温度下随cos2φ的变化规律.     

新型AgGa1-xInxSe2晶体用于CO2激光倍频研究

本实验室用布里奇曼方法成功生长出有应用前景的新型四元非线性AgGa1-xInxSe2晶体,对晶体光学透过,红外低倍显微成像,反射损耗和吸收系数进行了研究和计算.基于纯AgGaSe2和AgInSe2的Sellmeier方程,用线性内插方法计算了不同In含量的AgGa1-xInxSe2在0.9～19μm的Sellmeier色散系数并建立了Sellmeier方程.计算和描绘了Ⅰ型相位匹配CO2激光二次谐波产生的调谐曲线,并标出我们的倍频实验数据.在近似非临界相位匹配条件下,进行了TEA CO2激光10.6μm在AgGa1-xInxSe2中的倍频实验研究,并与AgGaSe2进行了比较,测量的1#AgGa1-xInxSe2相位匹配角θ及相位匹配接收外角△θext·L分别为88.2°和7.7°·cm,AgGa1-xInxSe2的倍频效率比AgGaSe2高出近3倍.     

Li2B4O7晶体在SAW技术中的应用研究

采用CZ法生长了30×30mm3的Li2B4O7单晶体.对晶体的压电性能进行了研究,弹性系数的交叉分量少,数值相对较小;在(001)面内有较高的声波传播速度,其变化范围为6500～7080m/s,在[001]方向有较低的声波传播速度,大约为5160m/s;而压电性能表明在不同方向的机电耦合系数均比石英晶体相应参数大得多.对晶体谐振器和压控震荡器的性能进行了研究,发现其机电耦合系数近似石英的十倍,很适合用来制作宽频器件.晶体谐振器的频率温度特性为抛物线型,其转变温度在室温,在-10℃～55℃温度范围内频率变化为3×10-4,具有良好的频谱响应,其寄生频率高出主振180kHz,衰减大于30dB,完全能满足器件使用要求.晶体滤波器3dB带宽的相对宽为1;,而石英仅为0.4;.     

The Effective Elastic Constants of Textured Polycrystals in Second Order Approximation

The effective elastic constants of textured polycrystalline materials are calculated in two approximations on the basis of a minimum energy assumption which is more realistic than the VOIGT and REUSS assumptions. The formulae are specified for the case of cubic crystal symmetry and orthorhombic specimen symmetry (sheet symmetry). Numerical values calculated for a copper and a steel sheet are compared with the corresponding experimental values.     

Lattice dynamics and related properties of AIBIII and AIIBIV compounds,I. Elastic constants

The present state of knowledge of the elastic properties of the ternary chalcopyrite compounds and some related materials is reviewed. Results of experimental elastic constant determinations are critically evaluated by comparing with other experimentally available material parameters that directly depend on the elastic constants. Possible reasons for existing discrepancies and obvious inconsistencies in the experimental data are discussed. The results of theoretical calculations of the elastic constants of these compounds based on different theoretical models and approaches are compared with experimental data and are assessed concerning achievable accuracy and reliability. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology of a Main Chain Liquid Crystal Polymer Containing Semi-Flexible Coupling Chain

A new procedure for the study of textures or director patterns in liquid crystal polymers is reported. The director patterns of the liquid crystal phase are decorated using a lower temperature crystalline phase, a process which does not disrupt the larger scale molecular organisation representative of the liquid crystal structure. The pattern of the decorating crystal lamellae is revealed using an etching technique; the director pattern lies orthogonal to these “lamellae”. Examples are shown of the texture relating to point and line defects. The potential of a quantitative approach to the director distribution about an inversion wall to provide numerical values of the curvature elastic constants is detailed.     

A general treatment of X-ray (residual) macro-stress determination in textured cubic materials: General expressions,cubic invariancy and application to X-ray strain pole figures

An expression in terms of general hkl and orientation distribution functions for the relationship between the elastic lattice strain measured by means of X-ray diffraction methods and the (residual) elastic stress is given for cubic textured materials. In practice the socalled sin² Ψ-method is often used to determine these macro stresses. Then, for the case of textured specimens the quasi-isotropic X-ray elastic constants (depending on hkl only) become complicated functions of the crystallographic texture (J. Appl. Crystallogr. 16 , 325 (1983)). Results are given for both orthorhombic and monoclinic specimen symmetry in terms of general (b.c.c. or f.c.c.) hkl and allow every permutation possible for a given hkl combination. From this cubic invariancy some new cubic invariant spherical surface harmonics are derived which are represented on a basis consisting of the 4-fold symmetry axes of the cubic crystals. Special textures and special stress-states are discussed. For a given texture of a cold-rolled production steel sheet values of the predicted elastic strains are given in terms of “X-ray strain pole figures”.     

Elastic properties of the pseudocubic perovskite (CsCd(NO2)3

Multidomain crystals of CsCd(No₂)₃ grown from aqueous solutions at about 310 K exhibit a quasi-cubic symmetry in their thermal expansion, elastic and thermoelastic properties. The elastic constants of the low-temperature multidomain state resemble the behaviour of stable cubic perovskites almost quantitatively. This suggests that the trigonal low-temperature phase of CsCd(NO₂)₃ possesses a quasi-cubic symmetry. The transition from the trigonal low-temperature phase into the cubic high-temperature phase at about 464 K is accompanied by a small deformation of about 10⁻⁴ and a lambda-type variation of the thermal expansion.     

Elastic and Thermoelastic Properties of Triclinic K2Cr2O7

Large single crystals of optical quality of triclinic K₂Cr₂O₇ have been grown from aqueous solutions. Their morphological and growth properties are not compatible with point symmetry 1 . Complete sets of the elastic constants and their temperature derivatives were determined from ultrasonic resonances of plane-parallel plates. The elastic behaviour and also the thermal expansion are highly anisotropic. Owing to very strong photoelastic effects these crystals are suited for certain acousto-optic deflection devices.     

Electrooptical coefficients and temperature and pressure derivatives of the elastic constants of tetragonal Li2B4O7

New values for the following properties of tetragonal Li₂B₄O₇ are reported: dielectric, electrostrictive, electrooptic, elastic, thermoelastic and piezoelastic constants, coefficients of thermal expansion and indices of refraction. These values are considered to be of superior precision compared to earlier published data. Most elastic constants possess positive temperature derivatives. This anomalous behaviour is not reflected in the pressure derivatives. The electrooptic effects are not large enough to compete with other materials used for technical applications.     

Elastic constant measurements of super ionic LiKSO4:Na single crystals

Elastic properties of sodium doped Lithium potassium sulphate, Li K_0.9 Na _0.1 SO_4, crystal has been studied by ultrasonic Pulse Echo Overlap [PEO] technique and are reported for the first time. The controversy regarding the type of crystal found while growth is performed at 35 °C with equimolar fraction of Li₂SO₄H₂O, K₂SO₄ and Na₂SO₄ has been resolved by studying the elastic properties. The importance of this crystal is that it exhibits pyroelectric, ferroelectric and electro optic properties. It is simultaneously ferroelastic and superionic. The elastic properties of LiK_0.9Na_0.1SO₄ crystal are well studied by measuring ultrasonic velocity in the crystal in certain specified crystallographic directions and evaluating the elastic stiffness constants, compliance constants and Poisson's ratios. The anisotropy in the elastic properties of the crystal are well explained by the pictorial representation of the surface plots of phase velocity, slowness and linear compressibility in a‐b and a‐c planes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stress,Strain, and Symmetry of Pseudomorphically Grown Epitaxial Layers

The complete stress and strain tensors and the point symmetry of pseudomorphically grown epitaxial layers are calculated from the epitaxial relationship and the elastic constants of the deposit material. The angle misalignment of crystallographic directions in the deposit due to the strain is also calculated and results are given for the epitaxial systems CaF₂/Si(100) and CaF₂/Si(111).