General principles of the synthesis of chalcogenides and pnictides in salt melts using a steady-state temperature gradient

The possibilities of growing crystals of metals, alloys, chalcogenides, and pnictides in halide melts using a steady-state temperature gradient are analyzed. Halides of alkali metals and aluminum can be used as transport media. The choice is determined by the melting temperature of salt mixtures. A conducting contour can also be applied to increase transport efficiency. This technique of crystal growth is similar to the electrochemical method. To eliminate interference during migration, some elements can be isolated and forced to migrate through independent channels to the crystal formation region. The technique considered here makes it possible to grow crystals of necessary quality without special equipment; the small crystal sizes are sufficient for laboratory study.     

电子背散衍射花样的数学特征

电子背散衍射(EBSD)花样揭示了材料的物相成分、晶体结构、晶粒取向、晶粒大小和晶界的信息。EBSD花样非常复杂,通常需要借助专门的计算软件才能解析。本文系统地研究了EBSD花样的数学特征,建立了任意晶体取向与EBSD花样之间的数理关系,推导了面心立方、体心立方和六方晶体的基本晶带轴的理论EBSD花样的数学特征,以及面心立方晶体的(001)<110>取向和(001)<100>取向的理论菊池(Kikuchi)花样特征。在实测EBSD花样的分析中与各晶系各点阵的基本晶带轴的理论EBSD花样特征比较,即通过图像特征对比,就可以直接确定实测EBSD花样所属的晶系、点阵和Kikuchi线交点对应的晶带轴[uvw],再由基本晶带轴的坐标计算出晶体取向,还能提供基本晶面信息,如原子密排晶面在样品中的空间分布,这有利于晶体的变形或生长机理研究。EBSD为单晶芯片质量检验提供了新方法。     

Steroid motor: dynamics of cholesteric helix induction in the nematic droplet

A nematic liquid crystal can be converted into a cholesteric phase by a chiral dopant, and the cholesteric pitch can be changed by its photochemical transformations [1]. For the first time we investigate the dynamics of the cholesteric phase induction using seven steroids (vitamin D isomers and related compounds) as chiral dopants. Here we report the new effect of rotation of a rod-like steroid crystal (0.1-1 mm length) when it is placed at the surface of a nematic drop and its dissolution course was followed with a polarizing microscope. For all the compounds univocal correspondence was noticed between the crystal rotation direction, the helicity of the molecular steroid ring system [2] and the sign of the cholesteric macrohelix determined by the Cano-Grandjean method [3]. No rotation was observed in the isotropic phase.     

硫镓银单晶生长新方法探索

在同一安瓿中一次性合成、生长出了外形完整、无裂纹的AgGaS2单晶体,尺寸达φ10mm×20mm.并进行了X射线能谱元素分析,测定了AgGaS2多晶粉末衍射谱,以及单晶体的红外透射谱,同时得到了(112)、(024)面的X射线单晶衍射谱,结果表明生长的单晶体可用于器件研究.     

Optimization of thermal conditions during crystal growth in a multi‐zone resistance furnace

The thermal condition is one the of most important control parameters for crystal growth. In this paper we present an effective numerical method in detail for optimizing thermal conditions in multi‐zone crystal growth facilities, especially for crystal growth by the float zone (FZ) technique. A furnace function Ω is introduced to integrate the character of a growth furnace into a linear equation system. The desired power distribution can be therefore approached by solving the linear equation system iteratively. An expert systemlike algorithm has been developed in order to obtain a more suitable solution for practical applications. This method was used to investigate thermal parameters for experiments of SiGe/GeSi single crystal growth by the FZ technique. It is an individual program which can be combined with any commercial finite element/finite volume (FE/FV) program such as FIDAP^TM.     

X-ray diffraction studies of protein crystal disorder

Protein crystals contain many kinds of disorder, but only a small fraction of these are likely to be important in limiting the diffraction properties of interest to crystallographers. X-ray topography, high-angular-resolution reciprocal space measurements, and standard crystallographic data collection have been used to probe three factors that may produce diffraction-limiting disorder: (1) solution variations during crystal growth, (2) macromolecular impurities, and (3) post-growth crystal treatments. Variations in solution conditions that occur in widely used growth methods may lead to variations in equilibrium protein conformation and crystal packing as a crystal grows, and these may introduce appreciable disorder for sensitive proteins. Tetragonal lysozyme crystals subjected to abrupt changes in temperature, pH, or salt concentration during growth show increased disorder, consistent with this mechanism. Macromolecular impurities can have profound effects on protein crystal quality. A combination of diffraction measurements provides insight into the mechanisms by which particular impurities create disorder, and this insight leads to a simple approach for reducing this disorder. Substantial degradation of diffraction properties due to conformation and lattice constant changes can occur during post-growth crystal treatments such as heavy-atom compound and drug binding. Measurements of the time evolution of crystal disorder during controlled crystal dehydration – a simple model for such treatments – suggest that structural metastability conferred by the constraints of the crystal lattice plays an important role in determining the extent to which the diffraction properties degrade.     

Laterally‐Graded SiGe Crystals for High Resolution Synchrotron Optics

A novel type of optical element for synchrotron radiation applications in the X‐ray region: namely laterally‐graded aperiodic crystals on the basis of Si_1‐xGe_x mixed crystal is presented. The lattice parameter of such gradient crystals containing up to some at. % Ge changes nearly linearly along the plane of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated. This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical synchrotron source divergence without a collimating pre‐mirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si‐crystal monochromator.     

Effect of the ultrasonic frequency on the multiple X-ray scattering from a LiNbO<Subscript>3</Subscript> crystal modulated by a surface acoustic wave

The effect of multiple scattering on the formation of the θ-2θ scan curves for a crystal modulated by a surface acoustic wave (SAW), depending on the ultrasonic frequency, has been investigated in the frame-work of the dynamical theory of X-ray diffraction. A model of a Rayleigh surface wave has been analyzed as applied to X-ray diffraction with allowance for the transverse and longitudinal elastic lattice strains. Using the example of the 127° Y′ cut of the LiNbO₃ crystal, it is established that the effects of multiple scattering can be neglected for ultrasonic frequencies above 650 MHz; this finding significantly simplifies the numerical calculations of X-ray diffraction from a crystal modulated by a short-wavelength SAW. A comparative quantitative analysis of the experimental data on synchrotron scattering from the 127° Y′ cut of a LiNbO₃ crystal modulated by a 952-MHz SAW have been performed, both taking into account and neglecting the effects of multiple scattering. It is shown that the computation time can be reduced by 2 to 3 orders of magnitude.     

Angular values and Delone tiling in crystal systems

A method is proposed for constructing angular values for Delone sets, which can be used as a basis to classify voids in crystal structures. An algorithm for determining the crystalline module in a crystal structure from the generalized void, including nonequivalent empty spheres of the corresponding symplectic Delone tiling, is considered (computer simulation).     

A new method of site occupancy analysis in substitutional mixed crystals by means of X-ray crystal structure analysis (I). Pseudo lattice and superposition structure of a substitutional mixed crystal

In Part I the nature of disorder in mixed crystal structures will be discussed on the basis of a pseudo lattice concept. A mixed crystal pseudo lattice applicable to all atomic positions of these mixed crystal structures will be defined, and the concept of a statistically globaldisordered ideal structure will be introduced. The structure factor for mixed crystal structures will be derived in consideration of the statistic disorder of position and sort of the atoms. The interpretation of the mixed crystal structure as a superposition structure requires the replacement of Vegard's rule by a new one having a wider range of validity.     

坩埚下降法生长La2Ti2O7晶体及其光性能研究

采用高温坩埚下降法生长La2 Ti2 O7晶体,获得的晶体尺寸约为18 mm× 12 mm× 10 mm,其表面出现了一系列(004)解理面.X射线双摇摆曲线表明该晶体具有良好的结晶质量.透过光谱显示退火后的La2 Ti2 O7晶体在可见光范围内是透明的,当波长在800 nm左右时,透过率将显著下降.La2 Ti2 O7晶体的吸收边出现在500 nm波长附近.光折射指数分析表明退火La2 Ti2 O7晶体具有高的折射率.折射率色散方程确定为n2(λ) =4.61643 +0.16198/(λ2-0.01547) -0.47201λ2,利用该公式可计算出300～1680 nm范围内任意波长下的折射指数n值.     

Two-level growth of potassium niobate KNbO3 single crystals: a new growth method for ABO3-type materials

Based on our recent study on the directional growth of KNbO₃ single crystals, a new growth scheme called the two-level growth (TLG) has been developed. By using the TLG method, high quality transparent KNbO₃ single crystals can be prepared with high reproducibility. The technique includes two growth stages. In level-one growth, a dimensionally defined (shaped) KNbO₃ seed with high crystal perfection is fabricated. The target crystal with desired dimensions and an architectural structure can be obtained in the second level of the growth. A process flow chart for the TLG method has been presented and six representative types of the growths have been introduced. Generally, crystals grown by TLG have much less crystal imperfections than those obtained from the conventional way. Technological merits of the TLG scheme have been studied, indicating that this growth scheme can also be employed to other oxide perovskite ABO₃ single crystal growths.     

壳聚糖分子对共沉淀法合成羟基磷灰石/壳聚糖粉体材料晶体形貌的影响

采用沸腾水浴共沉淀法,以尿素为pH调节剂制备羟基磷灰石/壳聚糖(HA/CS)复合粉体材料,通过XRD、FTIR和SEM对晶体组成、形貌进行表征,考察了壳聚糖平均分子量、添加量及反应物浓度对HA/CS晶体形貌的影响.结果表明,沸腾水浴共沉淀法可在较短时间内制备HA/CS复合粉体,改变反应物浓度可使晶体形貌由针状与球状同时存在转变为几乎全部是球状晶体,而CS平均分子量和添加量的影响较小.     

焦硅酸镥(Lu2Si2O7:Ce)闪烁晶体的生长与发光性能研究

铈掺杂的焦硅酸镥晶体(简写为LPS:Ce)是新近发现的一种具有潜在应用价值的无机闪烁晶体.本文用提拉法成功地生长出尺寸为φ15mm×40mm的LPS:Ce晶体.XRD结构测试表明,该晶体属于单斜晶系,C2/m空间群,晶体中分布有少量的LPS和石英颗粒包裹体.对从毛坯中切割出的无色透明晶体样品在室温下分别进行了透射光谱、紫外激发、X射线激发发射光谱和衰减时间测试.结果表明,铈(Ce3+)离子掺杂使LPS晶体的紫外吸收边从175nm红移到350nm,紫外和X射线激发的荧光光谱中都可以分解出384nm和412nm两个发射峰,它们分别对应于电子从铈(Ce3+)离子的5d轨道向4f轨道的两个能级(2F5/2和2F7/2)的辐射跃迁,从衰减曲线中可以拟合出一个38.75ns的时间常数.这些发光特征与该晶体独特的晶体结构密切相关.     

The effect of solvents and crystallization conditions on crystal habit of cholesterol

The effect of various organic solvents as well as the crystallization conditions on the crystal habit of anhydrous cholesterol have been studied. Both plates and needle-like crystals can be obtained in a particular solvent depending on the degree of supersaturation of the solution. However, the crystals grown at about the same supersaturation, from different solvents, show differences in their habit indicating dependence on the solvent-solute interaction. Thus, it is advisable not to identify needle-like crystals with anhydrous-cholesterol and plates with mono-hydrate cholesterol without specifying the crystallization conditions. A prediction on the crystal habit length to width ratios can be made using those parameters.     

一维纳米银柱、银棒及银线的生长机理研究

在纳米尺度范围,以合适的物理与化学方法可以得到纳米银的多种结晶形态及其聚形,得到简单的、复杂的孪晶;也可以得到平行连生生长成的纳米银柱、纳米银棒,得到以多重孪晶生长纳米银线.以结晶学、晶体结构、晶体化学理论为基础,研究了银纳米颗粒形成不同形态结晶的机理,探讨了一维纳米银柱、银棒与银线的不同生长机理.     

基于普通介质无缺陷一维光子晶体高Q值多通道滤波器

设计用常规介质构成的无缺陷的一维光子晶体,用特征矩阵法研究光波在其中的传输特性.在消逝波和传输波相互耦合的传播模式条件下,对特定的入射角度,有多个分离的高Q值频道可以让光波传播.因此可以将该结构用作多通道高Q值频率滤波器.通道位置和数目可以通过入射角度和结构的周期数目进行调节.     

提拉法生长高质量氟化镁单晶

设计了适合提拉法生长氟化镁单晶体的温场,采用提拉法成功生长出了直径100 mm的高质量氟化镁单晶.晶体内无气泡等宏观缺陷、无开裂;通过精密退火处理后,晶体透过率达到95;,平均应力双折射小于0.5 nm/cm.上述结果表明采用提拉法可以生长高质量的氟化镁单晶.     

Perfection and homogeneity of space-grown GaSb:Te crystals

A Te-doped GaSb crystal grown by the method of directed crystallization under microgravitation has been studied by X-ray topography. It is shown that the structural perfection of the crystal part grown without contact with the ampule walls is substantially higher than the structural perfection of the crystals grown under terrestrial conditions. The distribution of a Te dopant in the crystal is studied by quantitative X-ray topography, and it is shown that, if the gap between the growing crystal and the ampule is small, the Marangoni convection in the melt can be less intense than the convection provided by residual microgravitation. The relation between the formation of a flat face on the crystallization front (faceting) and the formation of twins is also established.     

Unsteady-state transfer of impurities during crystal growth of sucrose in sugarcane solutions

In this work, we present growth rate data of sucrose crystals in the presence of impurities that can be used by both sugar technologists and crystal growth scientists. Growth rate curves measured in a pilot-scale evaporative crystallizer suggest a period of slow growth that follows the seeding of crystals into supersaturated technical solutions. The observed trend was enhanced by adding typical sugarcane impurities such as starch, fructose or dextran to the industrial syrups. Maximum growth rates of sucrose resulted at intermediate rather than high supersaturation levels in the presence of the additives. The effects of the additives on the sucrose solubility and sucrose mass transfer in solution were taken into account to explain the observed crystal growth kinetics. A novel mechanism was identified of unsteady-state adsorption of impurities at the crystal surface and their gradual replacement by the crystallizing solute towards the equilibrium occupation of the active sites for growth. Specifically designed crystallization experiments at controlled supersaturation confirmed this mechanism by showing increasing crystal growth rates with time until reaching a steady-state value for a given supersaturation level and impurity content.