Growth, Structural and Microhardness Studies on New Semiorganic Single Crystals of Calcium Para Nitrophenolate Dihydrate

Good quality crystals of calcium p-nitrophenolate （NPCa） were grown from saturated solution by slow evaporation method. The crystal structure analysis and the molecular arrangement of these crystals were determined using X-ray diffraction （XRD）. From Single crystal XRD studies, NPCa is found to be crystallized in the mon- oclinic system with a space group P21/n. The functional groups of the material were confirmed qualitatively by F-FIR （Fourier transform infrared spectroscopy） spectral analysis. Optical absorption studies reveal the absorption region and microhardness studies were carried out to confirm the mechanical behaviour of the crystals.     

Effect of Seed Sizes on Growth of Large Synthetic Diamond Crystals

For the growth of large synthetic diamond crystals by temperature gradient method （TGM）, the grit sizes of seed crystals have great effects on the growth rate and quality of large grown crystals. Because of the limited area of seed surfaces, the maximum diffusion flux of carbon source, which could be absorbed by the seed, is related to the seed size. And with increasing the seed sizes, the growth rates also increase markedly. However, the seed sizes should be lower than a certain value, which determines the crystal quality directly. For example, with NiMnCo alloy as the metal solvent, when the seed size increases from 0.5 to 1.8 mm, the growth rate increases greatly from about 1.1 to 3.2 mg/h; when the size is beyond 2.0 mm, more and more metal inclusions would be incorporated into the grown crystals, and the crystal quality is destroyed heavily. Finite element analysis （FEA） shows that, due to the special assembly of growth cell, the diffusion of carbon source in the metal solvent is very inhomogeneous, which could be substantiated directly by the appearances and shapes of large grown crystals and the remains of carbon source. And this inhomogeneous diffusion of carbon source would be very harmful to the growth of large diamond crystals, especially when large-size seed crystals are used.     

The catalytic activity of space versus terrestrial synthesized zeolite Beta catalysts in the Meerwein Ponndorf Verley Reactions: Support for PFAL as the Lewis active site for cis-alcohol selectivity

The Lewis activity of the Meerwein-Ponndorf-Verley (MPV) reactions is hypothesized to be due to partial framework aluminum (PFAl) that is either octahedrally or tri-coordinated. Crystals grown in the free-fall environment of low earth orbit (LEO) are more uniform; that is, have fewer lattice “defects” compared to those grown in a gravity field (i.e., on earth). Therefore, crystals grown in orbit should be less catalytically active relative to their earth grown counterparts. The catalytic activity towards the MPV reaction, and the associated IR and XPS spectrum for zeolite Beta that was synthesized on earth (1g) and aboard the International Space Station (10⁻³–10⁻⁵g) were compared in their as-synthesized forms, and after applying heat treatment protocols designed to stress the crystal structure to generate Lewis acid sites (i.e., tri and octahedrally coordinated PFAl). The activity of the MPV reaction and cis-alcohol selectivity over the heat-treated flight samples was observed to be lower than the identically heat-treated terrestrial zeolite Beta samples. Higher MPV activity as well as cis-alcohol selectivity is related to both a higher number of partial framework Al atoms (PFAl), and a constrained pore volume. As PFAl are created by the destruction of the framework upon heat treatment, flight samples were shown to be thermally more stable with fewer lattice defects and less associated stress in zeolite Beta crystals. The changes observed in the IR spectra, as well as the XPS Al Auger and 2p peaks, of the terrestrial samples support this conclusion. Additionally, the flight samples showed higher tr-alcohol selectivity, which implies more pore volume and less channel blockage. This is consistent with the fact that crystals grown in space have less stress, fewer lattice defects, and thus there are fewer channel obstructions.     

穗状晶形成及其结构的研究

凝固过程中的流体流动效应是现代凝固科学研究的热点,尤其是流动与凝固界面的耦合作用及流动对生长成的晶体质量的影响。作者自行设计了一套带有对流驱动系统的强制性晶体生长装置,可以实现液相层流作用下的晶体生长过程,而且流动的发生及流速的改变极为方便。利用透明模型合金 SCN-2%wt.Ace 作为研究对象,详细考察了液相快速流动作用下的强制性晶体生长的行为,首次发现了一种新的晶体形态——穗状晶;作者对其结构和形成过程进行了详细分析,并预示了这种结构的潜在应用价值。     

二磷酸钕钾晶体的生长与光谱

Ｋ３Ｎｄ（ＰＯ４）２晶体是一种高稀土浓度的激光晶体．本文报道从ＫＦ－ＫＣｌ体系中采用助熔剂法培养出Ｋ３Ｎｄ（ＰＯ４）２晶体．该晶体呈淡紫红色，属单斜晶系，Ｐ２_１／ｍ空间群，晶胞参数为ａ＝９．５３４　，ｂ＝５．６２９　，ｃ＝７．４４３　，β＝９０．９６°．测定了晶体室温下的吸收光谱、荧光光谱、激发光谱和红外光谱．     

Effect of Ni on the structural, optical, thermal and dielectric properties of ADP single crystals

The effects of the addition of Ni²⁺ on the growth and various properties of ammonium dihydrogen phosphate single crystals grown from aqueous solution by the slow evaporation method have been studied. The grown crystals were subjected to HRXRD, UV-Vis, TG/DTA and dielectric studies. The structural perfection of the grown crystal has been analyzed by high resolution X-ray diffraction rocking curve measurements. UV-Vis studies show that the grown crystal has good transparency in the entire visible region which is an essential requirement for a nonlinear crystal. Higher decomposition temperature was observed from TG/DTA. Dielectric constant and dielectric loss were measured for the grown crystal for different frequencies and temperatures.     

Crystal growth, structure and characterizations of a new semiorganic nonlinear optical material—β-Alanine zinc chloride

The title compound, β-alanine zinc chloride—a new semiorganic nonlinear optical crystal was grown by slow evaporation technique. Single crystals of β-alanine zinc chloride have been subjected to X-ray diffraction analysis to determine the crystal structure. The powder X-ray diffractogram of the crystal has also been recorded. The amount of carbon, nitrogen and hydrogen in the crystals was also estimated. Fourier Transform Infrared and Raman spectral measurements have been carried out on the grown crystals in order to identify the functional groups. The presence of hydrogen and carbon in the β-alanine zinc chloride was confirmed by using proton and carbon nuclear magnetic resonance spectral analyses. The percentage of zinc in the crystal was determined by atomic absorption spectroscopy. Optical behavior such as ultraviolet-vis-near infrared transmittance spectrum and second harmonic generation has been investigated. The mechanical strength and thermal behavior of the grown crystal have been analyzed.     

F/Cl比对PbFCl晶体生长和发光性能的影响

PbFCl是一种具有双读出功能的闪烁晶体, 性能优异但制备困难。本研究通过调整PbFCl原料组份, 探索F/Cl摩尔比(F/Cl)对晶体生长、透光和发光性能的影响。实验结果表明, 原料配方中适量富Cl有利于生长出透明晶体, 但会加剧解理。组分偏析会使晶胞参数略有改变, 而对物相没有影响。X射线激发光谱发光峰位不随F/Cl比改变而移动。透过光谱显示PbCl₂组份增加, 紫外吸收边会从300 nm蓝移至275 nm附近, F/Cl变化不引入新的吸收峰, EWT计算表明F/Cl=1:1.25时晶体的双读出性能最好。     

Copper (II) oxide as a morphology directing agent in the hydrothermal crystallization of magnetite

Magnetite crystals with unique morphological characteristics have been grown from hematite under hydrothermal conditions at 150 and 175 °C in the presence of hydrazine and copper (II) oxide. In the absence of CuO, octahedral crystals of magnetite with a distribution of particle sizes were grown in accordance with literature procedures. In the presence of CuO, magnetite crystals with distorted morphology were prepared in which the [111] crystal faces were absent, leaving a framework structure of corners and edges. Examples of crystal intergrowths were observed, as well as the partial collapse of the framework structure of the magnetite. The results are discussed with reference to the possible effect of copper redox couples on the hematite reduction reaction.     

碲化锡材料的制备及其特性研究

用Bridgman法合成SnTe晶体,并用X射线衍射仪测试其显微结构,发现其晶格常数比标准值略小.以制备的晶体为原料用真空蒸镀法制备了银灰色SnTe多晶薄膜,并对薄膜的显微结构、伏安特性及表面形貌进行了研究.结果发现,薄膜上晶粒的生长有一定择优取向,其伏安特性曲线有突变点,通电后薄膜表面的原子形成了团簇.     

蓝宝石单晶的气孔形成研究

采用冷心放肩微量提拉法(SAPMAC法)生长的蓝宝石晶体, 气孔是其主要缺陷. 本文探讨了影响气孔形成的工艺因素, 从晶体生长动力学角度分析了气孔形成机理. 结果表明, 通过优化温场、选择合适的生长速度及控制微凸固/液界面形状, 可有效降低晶体中气孔的数量.     

Band gap enhancement on metal chelation: Growth and characterization of cobalt chelated glycine single crystals for optoelectronic applications

Single crystals of Diaqua Bisglycine Cobaltous Chloride (DBGCoCl) have been synthesized and grown by slow evaporation method. Grown crystals were subjected to FTIR and XRD studies for structural confirmation. The DBGCoCl crystallizes in the monoclinic system with the space group P2₁/c. The UV–vis spectrum for the pure glycine as well the cobalt chelated glycine have been recorded. The lower cutoff wavelength observed from the UV–vis spectrum is found to decrease by the chelation of cobalt with glycine and this leads to an increase in the band gap of the compound from 3.13 eV to 4.91 eV. The optical constants were calculated and illustrated graphically. Mechanical hardness of the grown crystal DBGCoCl was studied and Vickers hardness number was calculated. The work hardening coefficient (n) was determined to be 1.365 and the stiffness constants for different loads were calculated and reported. The thermal stability of the grown crystal has been studied using TGA and DTA. The crystal is thermally stable up to 116.86 °C.     

Morphology of C60 Crystals Grown from the Vapor Phase

Abstract

The morphology of C₆₀ crystals grown from the vapor phase have been studied. In all observations, only hexagonal and rectangular shaped crystal faces were found. Very different morphology, highly faceted {111} faces and flat {100} faces were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). the highly regular shape and similar distance between all neighboring macrosteps observed for the {111} faces can be explained by taking into account that edges of two adjacent {111} and {100} planes can act as step sources.     

Structure et anomalie dielectrique de Tl2Ta2O6

Single crystals of the pyrochlore Tl₂Ta₂O₆ have been grown in a flux of thallous carbonate under pressure of carbon dioxide at 900°C. The crystal structure has been refined in the cubic space group Fd3m from 93 independent reflections. The problem of thallium localization along [111] axis is discussed. The dielectric properties show that the real space group cannot be Fd3m at temperatures less than 560°K.     

大尺寸6H-SiC半导体单晶材料的生长

报道了生长SiC单晶的PVT法生长工艺,研究了晶体生长温度、温度梯度、生长室压力、杂质等因素对晶体生长和晶体质量的影响,确定出合理的工艺条件,生长出φ45mmSiC单晶.X射线衍射表明,生长的单晶为6H多型结构,通过腐蚀法得到晶体中微管道密度约为10³cm^-2,位错密度约为10⁴～10⁵cm^-2.测试了SiC单晶的半导体特性,结果表明:晶体为n型,电阻率约300Ω·cm,迁移率90cm2V^-1S^-1,载流子浓度在10¹⁴cm^-3量级.     

Crystal growth, thermal and optical studies of semiorganic nonlinear optical material: l-lysine hydrochloride dihydrate

Single crystals of l-lysine hydrochloride dihydrate (LLHCD), a nonlinear optical material, have been grown by slow cooling technique from its aqueous solution. LLHCD was found to be highly soluble in water. The grown crystals have been subjected to single crystal X-ray diffraction to confirm the structure and to estimate the lattice parameters. The vibrational structure of the molecule is elucidated from FTIR spectra. Thermal analysis revealed the thermal stability of the grown crystals. The optical transmittance spectrum shows that the material possesses good optical transparency in the entire visible region with a UV cut-off wavelength at 228 nm. The mechanical properties of the grown crystal have been studied using Vicker's microhardness test. The laser damage threshold of 52.25 MW/cm² has been measured by irradiating Q-switched Nd:YAG laser (1064 nm).     

光子晶体传感器的研究进展

光子晶体是一类具有光子能带和带隙的新型光学材料,近年来已成为传感器技术领域的研究热点。光子晶体微腔、光子晶体波导、光子晶体光纤在传感器领域得到了广泛应用,而凝胶光子晶体、反蛋白石光子晶体、分子印迹光子晶体则实现了化学生物传感器的"裸眼检测技术"。重点分类介绍了一维、二维、三维光子晶体的制备及其在传感器领域的应用进展。     

Growth and single crystal XRD characterization of undoped and doped 4-hydroxyacetophenone

Good quality 4-hydroxyacetophenone and nitro-doped 4-hydroxyacetophenone crystals have been successfully grown from saturated methanol solution by slow cooling method. Then, 3-nitro-4-hydroxyacetophenone is incorporated as a dopant into single crystals of 4-hydroxyacetophenone to enhance the NLO property. The crystal structure and the packaging of molecules along the “a” and “c” directions have been obtained by single crystal X-ray diffraction studies. The mechanical properties of the grown crystals have been analysed using Vicker's microhardness tester.     

物理气相传输法生长碳化硅单晶原生表面形貌研究

晶体的生长原生面在一定程度上能反应出晶体生长机制和晶体缺陷分布的丰富信息。采用激光共聚焦显微镜偏光拼接技术和原子力显微镜对物理气相传输法生长的4H、6H-SiC单晶原生小面的表面形貌进行了观察和测试。偏光显微镜和原子力显微镜测试结果显示4H-SiC原生小面扩展后, 其周边趋向于形成六边形的生长台阶; 而6H-SiC原生小面扩展后, 其周边趋向于形成圆形的生长台阶。基于Jackson双层界面模型, 从热力学角度计算了4H、6H-SiC单晶的Jackson因子α分别为33.15和31.87, 故导致4H、6H-SiC单晶原生小面台阶形貌差异的是生长界面的粗糙程度和生长温度。原生面上的微管缺陷是生长台阶的起源, 借助原子力显微镜对多个微管进行了测试。由测试结果可知, 微管直径分布在760 nm-6.0 um之间, 相应的伯格斯矢量绝对值分布在5c~14c, 微管直径与伯格斯矢量平方值的商D/B²分布在11.1~23.6 nm^-1之间, 即通过原子力显微镜测试获得的微管结构数据不严格遵守Frank理论。     

超化学计量比氧化铀晶体的研究进展

氧化铀不仅是重要的核材料, 也是潜在的多功能材料。UO₂晶体具有优异的半导体性能和抗辐照能力, 其禁带宽度(1.3 eV)与Si(1.1 eV)相近, 塞贝克系数是常用热电材料BiTe的4倍, 对太阳光的全吸收使其成为高效的太阳能电池材料, 在半导体、太阳能和热电等领域具有巨大的应用潜力。但是UO₂随着环境变化会出现从缺氧到过氧的价态变化(UO_2±x, x= -0.5~1), 即超化学计量比特性, 给材料制备和性能控制等方面带来很多问题。本文从相图出发, 总结了各种铀氧化物的结构及其稳定性, 重点聚焦UO₂晶体的研究进展。理想化学计量比UO₂被认为是最好的Mott绝缘体, 其电导率是相对稳定的; 超化学计量比氧化铀则具有半导体特性, 其电导率、热导率、扩散系数以及光学性能都与x密切相关。目前, UO₂晶体生长主要采用化学气相输运法(CVT)、冷坩埚法、水热法、升华法、助熔剂法等, 晶体尺寸和质量还不理想, 冷坩埚法和水热法被认为是最有潜力的生长技术。氧化铀单晶生长研究不仅有助于深入了解UO₂材料特性, 也为其在太阳能电池、热电器件以及未来电子学领域的应用提供可能性。