X-Ray Topographic Investigation of Dendritic Silicon Crystals

Using Lang and double-crystal X-ray topographic methods the dislocation structure of dendritic silicon crystals have been investigated. It is shown that the surface layers of these crystals have a more perfect structure than their bulk volume. The twin lamella is a dislocation-free formation and there are dislocation-free zones ∼ 1,5 mm in width in the volume of crystals.     

X-ray topographic study of quartz crystals with induced growth striations

The method of “induced growth striations” was applied to the hydrothermal growth of quartz crystals. Striations were due to a periodical modulation of the growth temperature induced and investigated by means of the X-ray Lang topography and plane wave reflection topography. The results show that the X-ray topographic methods are a sensitive tool for the characterization of the growth striations, which are produced generally by Al impurities. The application of the method of induced growth striations to quartz crystals and the characterization of these crystals with optical and X-ray topographical methods allow a deeper understanding of the crystal growth behaviour.     

Preparation and characterization of superfine ammonium perchlorate (AP) crystals through ceramic membrane anti-solvent crystallization

In this paper, a novel ceramic membrane anti-solvent crystallization (CMASC) method was proposed for the safe and rapid preparation ammonium perchlorate (AP) crystals, in which the acetone and ethyl acetate were chosen as solvent and anti-solvent, respectively. Comparing with the conventional liquid anti-solvent crystallization (LASC), CMASC which successfully introduces ceramic membrane with regular pore structure to the LASC as feeding medium, is favorable to control the rate of feeding rate and, therefore, to obtain size and morphology controllable AP. Several kinds of micro-sized AP particles with different morphology were obtained including polyhedral-like, quadrate-like to rod-like. The effect of processing parameters on the crystal size and shape of AP crystals such as volume ratio of anti-solvent to solvent, feeding pressure and crystallization temperature were investigated. It is found that higher volume ratio of anti-solvent to solvent, higher feeding pressure and higher temperature result in smaller particle size. Scaning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the resulting AP crystals. The nucleation and growth kinetic of the resulting AP crystals were also discussed.     

近化学计量比Tb:Fe:LiNbO3晶体的光谱特性及组分测定

按化学计量比,用提拉法成功生长了不同掺量的Tb:Fe:LiNbO3晶体,分别测量了掺杂LiNbO3晶体在紫外(313nm)曝光前后的吸收光谱,曝光后吸收谱线整体上移,找到了吸收谱线上移最大的掺量比.并用差热分析仪DTA测量了居里温度Tc, 从而计算出Li/Nb的比例.分析表明,Tb:Fe:LiNbO3晶体的存储性能与掺量、定比有密切的联系,是一种优良的大容量体全息记录材料.     

Microhardness investigations on gel-grown barium cadmium oxalate mixed crystals

Microhardness characteristics of barium-cadmium oxalate crystals were undertaken using the indentation technique and the results there of are reported. The observed results were compared with the microhardness values of barium oxalate dihydrate and cadmium oxalate trihydrate crystals. The indentation induced cracks etched in 1N HCl reveal the surface of the dislocation pattern arround indentation mark. The mixed crystals show higher values of microhardness than the components barium oxalate dihydrate and cadmium oxalate trihydrate crystals.     

Study of the crystal device for deflecting high-energy proton beams using synchrotron radiation diffraction

Currently, bent silicon single crystals are used at large accelerators to extract and collimate proton beams. A device for multiple deflection of a proton beam based on several bent silicon strips operating in the volume reflection mode has recently been developed. In this device, the bending of silicon strips successively located on the surface of a thick plate is implemented due to the internal stress induced by grooves mechanically formed on the crystal surface (Twyman effect). Topography based on angular scanning and synchrotron radiation was applied to measure the bending of individual deflector strips and the crystal as a whole. The measurement results are compared with the data obtained with a proton beam.     

掺杂LiNbO3晶体的生长缺陷与其体全息存储性能的研究

本文叙述了利用侵蚀法研究掺杂LiNbO3的晶体缺陷,并讨论了晶体缺陷的形成机理以及其与体全息存储性能的关系.通过实验发现了常温下侵蚀铌酸锂晶体的规律,并利用侵蚀法观测到铌酸锂晶体样品表面呈三角锥状的位错侵蚀坑.测量了晶体样品的散射噪声,从中找出了晶体缺陷与存储图像质量关系.并发现掺Zn的Fe:LiNbO3晶体其晶体缺陷减少,晶体体全息存储性能有了明显提高.     

Influence of Ionizing Radiation on Performance of Nd:YAG Lasers

For crystals annealed in oxidizing atmosphere the influence of the dose on the shape of additional absorption spectrum of Nd:YAG samples after gamma and proton (energy of the order of 26 MeV) irradiation's was described. Changes in optical output of Nd:YAG laser after different value of gamma's dose were determined. The Nd:YAG crystals were also irradiated with 1 MeV electrons coming from Van de Graaf accelerator. Changes induced in the defect structure of the irradiated crystals were described.     

The combined effects of supersaturation and Ba2+ on the batch cooling crystallization of potassium dihydrogen phosphate

The combined effects of supersaturation and Ba²⁺ on potassium dihydrogen phosphate (KDP) were investigated in batch cooling suspension crystallization. Growth size, morphology, and impurity Ba²⁺ adsorbed in the KDP crystals were measured with changing Ba²⁺ concentration and supersaturation. Significant changes in shapes and volume of the grown crystals have been observed. The results further confirmed that the size and shape of crystals were greatly determined by supersaturation. Ba²⁺ ions significantly modified the growth habit of KDP crystals. The concentration of Ba²⁺ ions adsorbed in the crystals increases with the increasing Ba²⁺ ions in the solutions and supersaturation. The foggy phenomena caused by the addition of Ba to the KDP solution were also described. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and properties of Ba‐doped KDP crystals

KDP crystals were rapidly grown from solution doped with different Ba²⁺ concentrations. The effects of Ba²⁺ on the growth rate, morphology and quality of KDP crystals were discussed. Significant changes in shapes and volume of the grown crystals have been observed. During the growth process, defect region expands gradually with the increasing Ba²⁺ concentration. Samples were cut from different parts of the as‐grown crystals for investigating the optical quality, including transmission spectrum, scattering centers. Through comparison, it is found that the nonuniform distribution of Ba²⁺ ions causes remarkable difference in optical quality between prismatic and pyramidal sectors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of 50 MeV Si ion irradiation on nonlinear optical benzimidazole single crystals

The 50 MeV Si⁷⁺ ion irradiation induced modifications on structural, dielectric, optical and mechanical properties of Vertical Bridgman grown benzimidazole (BMZ) crystals were studied. The high resolution X‐ray diffraction studies show the quality of as grown BMZ and irradiated BMZ crystals. The dielectric constant and dielectric loss as a function of frequency and temperature was studied in detail. The ion induced mechanical behaviour of both as grown BMZ and irradiated BMZ crystals has been explained with the indentation effects using Vickers microhardness tester. UV‐VIS. studies reveal the decrease in bandgap values and defects on irradiation. The above results are discussed in detail. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-Ray Topographic Investigation of Silicon Single Crystals Heavily Doped with Sb

Heavily Sb doped silicon crystals grown by Czochralski method were investigated using X-rays methods. It is shown that growth striation contrast is caused by inhomogeneous Sb distribution. While approaching the lower part of crystals their volume is being contaminated by dispersive particles of noncontrolled impurities that results in decrease of anomalously transmitted X-rays and weakening of the contrast in topographical growth striation image. In the canal connected with the facet effect crystal structure is less damaged by foreign inclusions.     

Observation of concentration boundary layers around growing or dissolving KH2PO4 crystals in stagnant solutions

The solute concentration profiles around KH₂PO₄ crystals growing or dissoloving in stagnant aqueous solutions were studied by the schlieren method after Toepler. By this technique the thicknesses of concentration boundary layers around the crystals, formed by free convection of solution, were measured in dependence of crystal size and super (under) saturation. In the case of dissolution, theoretical estimation of the boundary layer thickness yielded a fair agreement with the observed value. For growth, the process is dominantly limited by surface kinetics, whereas volume diffusion plays a minor role.     

Structural and Density Changes of Rhenium Single Crystals Upon Rolling and Annealing

The rhenium crystals were rolled in the {1000} 〈112 0〉 orientation. Rolling produces cracks in crystals at low deformation (ϵ = 30%). It has been shown that microcracks in the volume of the crystal arise at a more earlier deformation stage than visible surface cracks. Recrystallization during subsequent annealing is strongly intensified with the start of crack formation. Stepwise facets of recrystallizated grains are often observed, this fact being connected with twinning lamellae recrystallization. Microcracks in the crystal body are completely eliminated during high temperature annealing. This process caused by diffusion over microcracks surfaces.     

DNA模板调控纳米无机材料生长

以DNA为模板诱导纳米无机晶体的生长是近年来一个新的研究方向.DNA模板具有完善和严密的分子识别功能,使其组装过程具有高度的选择性.通过人为控制DNA的形状、长度和序列,可以制备出不同结构的纳米功能材料.本文讨论了DNA模板诱导硫化镉、四氧化三铁、硫酸钡、氯化镁和二氧化硅等纳米无机晶体的生长.     

Crystallization statistics. A new tool to evaluate glass homogeneity

We propose and test a new method to evaluate the chemical homogeneity of glasses based on statistical analyses of the volume distribution of crystals developed through thermal treatments. The method is based on the fact that each volume element of a glass piece subjected to a proper thermal treatment should exhibit a certain number of crystals, which is dictated by its chemical composition. We performed numerical simulations to interpret the experimental results obtained for some glasses, and demonstrate that this new method is adequate to determine the degree and scale of heterogeneity of glasses that display volume crystallization.     

Photoswitching of Helical Twisting Power by Chiral Diarylethene Dopants

Abstract

Photochromic chiral compounds having two diarylethene units were synthesized in an attempt to use them as dopants for photoresponsive liquid crystals. Stable photoswitching of the photochromic dopants induced large pitch changes of chiral nematic liquid crystals composed of K-15 and a small amount of the chiral dopants.     

Magnetic Levitation Force of Bulk YBaCuO Pieces as a Function of Texture

Very well textured YBaCuO forms can be produced by means of seed crystals implanted in an YBaCuO melt. Narrow distributions of the directions (FWHM < 6°) of the c‐axes of the crystalline grains as well as the a‐ and b‐axes, respectively, are required for this purpose. Small angles between the c‐axes of adjacent grains, and small angles between the a‐ and b‐axes, respectively, of the neighbors, constitute but small obstacles in the path of the superconducting current induced. If the entire volume of the melt‐textured forms, in this case YBaCuO cylinders, is well textured, and if no random volume fractions remain, a maximum inducible superconducting current in the superconductor can be achieved and, thus, a maximum magnetic repellent force against the inducing permanent magnet, can be attained. This ensures maximum magnetic levitation force for a superconducting self‐stabilizing magnetic bearing.     

Effect of high oxygen doping on the minority carrier lifetime in heat-treated silicon crystals

Effect of high oxygen doping on thermally induced changes in the minority carrier lifetime τ in 800 °C heat-treated silicon crystals is studied and analyzed. Deteriorated τ values in prolongly annealed highly oxygen-enriched Si crystals compared with those found in annealed oxygen-poor crystals, are observed. This is explained by an appearance in prolongly annealed highly oxygen-enriched silicon crystals of oxygen-induced microdefects which are effective in the minority carrier recombination.     

The influence of OH−-ions on the mechanical properties in LiF and NaCl single crystals

The influence of the growing atmosphere on the mechanical properties was investigated on LiF and NaCl single crystals. The growing atmospheres were air or vacuum and argon, respectively. In a wide temperature range the air grown crystals have a higher flow stress and a smaller activation volume. Besides, the dislocations are less mobile. The differences arise probably from the OH⁻-ions, which were found in a considerable concentration in the air grown material. The OH⁻-ions may create lattice distortions by themselves or by the formation of different complexes with the divalent cation impurities. In this way the density of thermal and athermal obstacles for the dislocation motion increases.