共查询到19条相似文献,搜索用时 234 毫秒
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同样由熔体凝固、溶液沉淀或者气相沉积出来,为什么有的材料呈晶相,有的呈非晶相? 晶体生长是由自组装形成的还是由外界条件决定的?是哪项因素决定了晶体生长时原子的有序排列?本文根据实际现象,用晶体生长的热力学理论分析了逆向离子解离对晶体成核及生长的作用机理,并对固态材料的形成与晶体成核生长之间的关系也作了进一步的阐述和分析,由此得出结论认为,由化学键结合的材料在晶体生长时必须伴随着逆向离子解离平衡,正是固态材料形成过程中的逆向离子解离过程,如同时伴随着电离的溶解、熔化及升华过程,决定了晶体生长时原子的有序排列. 相似文献
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溶液、熔体中负离子配位多面体生长基元的分布与缔合 总被引:10,自引:4,他引:6
根据对晶体生长溶液、熔体拉曼光谱的测试结果,剖析了溶液和熔体中负离子配位多面体的分布及其缔合过程,总结出了不同过饱和溶液和不同过冷度熔体中负离子配位多面体生长基元的缔合形式和维度的规律.在靠近晶体的边界层处已出现与晶体结构相同或相似的大维度生长基元.实验表明,生长基元的分布和缔合与溶液过饱和度和熔体过冷度密切相关,从而提出用拉曼光谱进行实时监控,寻找最佳生长物化条件,优化晶体生长边界层的厚度和大维度生长基元的数量,为选择最佳工艺条件提出理论依据. 相似文献
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Ju. Linhart Myron Pankevich 《人工晶体学报》2004,33(2):144-151
本文的计算方法是根据对晶体生长炉中温场和热交换状态的实验研究提出的.用这种计算已成功地生长出大尺寸的CaF2和BaF2晶体(直径φ400mm),计算方法的准确性已为实验所证实,在许多新建或现有的生长系统中,结果都证明这种计算方法对于解决一些生长和退火问题是有效的.这种方法被广泛地用于估计各种复杂结晶容器的边界条件和在大晶体生长各个阶段的连续温场处理模型.这一点非常重要,因为迄今除了计算以外还没有其它方法可用于分析碱卤化合物材料的熔体-晶体系统的热状态,在用Stockbarger技术中,这些实验结果被成功地用于发展生长设备. 相似文献
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铁电铌酸钾锂晶体的生长 总被引:3,自引:1,他引:2
用电阻加热引上法生长了不开裂、全透明的具有倍频性能的铌酸钾锂(KLN)晶体.研究了影响晶体开裂的主要因素和晶体生长的稳定性.发现用引上法生长KLN晶体时,要得到全透明、不开裂的KLN晶体,熔体中Li2O的含量应该低于26.5mol;,拉速应低于0.5mm/h,以及生长过程中应该选择凸的固液界面以保证晶体生长的稳定性.在Li2O含量较高的熔体中生长KLN晶体时,[100]取向的籽晶比[001]取向的籽晶更有利于晶体生长.用由Li2O含量为26mol;的熔体中沿[100]取向生长的KLN晶体对Ti:Al2O3激光器输出的820nm的激光倍频,获得410nm的蓝光输出. 相似文献
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Y.Z. He Y.G. Zhao M.H. Zhu X.P. Zhang B.S. Cao 《Crystal Research and Technology》2002,37(12):1280-1284
A facile method to control the contracting rate of the thermal expansible bars for pulling crystal is first suggested. The thermal expansible bars, set in a modified Dewar flask whose vacuum degree is controlled, are heated to designed temperature and then switch off the power to let it cool down at a desired rate, which depends largely on the changeable vacuum degree. This new approach is expected to completely eliminate the effects, which possibly reduces the smooth extent of thermal expansion, caused by the minor temperature fluctuations during crystal growth process and to realize the utmost smooth and slow pulling rate. It is expected to install this apparatus in optical floating zone furnace, instead of traditional motor, to grow peritectic crystal, such as crystal Bi‐2223, since for the peritectic reaction, in principle, the extremely slow growing rate is considerably essential. 相似文献
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新型有机非线性光学晶体-L-苹果酸脲晶体生长的初步探讨 总被引:2,自引:2,他引:0
本文初步探讨了新型非线性光学晶体-L-苹果酸脲的晶体生长,研究结果表明,L-苹果酸脲晶体在甲醇、乙醇和水三种介质中的溶解度温度系数均较大,同温度下L-苹果酸脲晶体在水中的溶解度最大,无水甲醇次之,无水乙醇中最小.L-苹果酸脲晶体在无水甲醇中的成核自由能比在无水乙醇中的低得多,因此在无水甲醇中易于成核,晶核数多,晶体尺寸小,而在无水乙醇介质中,虽然成核相对比较困难一些,但有利于制备大的单晶,且发现低温有利于大晶体的生长.因此宜选择无水乙醇为晶体生长介质.L-苹果酸脲晶体在介质中以非均匀成核方式在试管壁成核长大,晶体呈棱柱状,生长过程中呈现台阶生长的特征. 相似文献
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Chen Songyan Liu Baolin Wang Benzhong Huang Meichun Chen Longhai Chen Chao 《Journal of Crystal Growth》1997,170(1-4):433-437
Lattice-mismatched heteroepitaxy has attracted considerable attention in recent years. A great interest of these systems is the possibility of integrating devices from different materials on a single substrate. 1.3 and 1.5 μm InGaAs(P)/InP laser diodes are essential for optical communication, whereas InP field effect transistor technology is less developed than that of GaAs MESFET. The performances of laser diodes are much more sensitive to a high density of disclocations, so it would be interesting to grow GaAs MESFET on InP for integration with 1.3 and 1.5 μm lasers. Due to the large difference of the thermal expansion coefficient and lattice parameter between GaAs and InP, it is very difficult to grow GaAs epilayers of high quality on it is very difficult to grow of GaAs epilayer high quality on InP substrates due to the large difference of the thermal expansion coefficient and lattice parameter between GaAs and InP. A new method, metalorganic source modulation epitaxy (MOSME), which improves the crystal quality of GaAs epilayers on InP substrates by MOVPE, has been adopted in our laboratory. The lowest full width at half maximum (FWHM) of the double crystal X-ray (DCX) diffraction spectra reaches as low as 120 arcsec for a 5 μm thick layer. Structural properties (misorientation, lattice parameters and crystal quality) of 1.0–5.0 μm thick GaAs layers grown on InP have been measured by DCX diffraction. On GaAs MESFETs grown on InP, we have measured gm = 100 ms/mm. For these transitions, the current gain cut-off frequency (Ft) is around 12 GHz and the maximum frequency of oscillation (Fmax) is higher than 30 GHz. 相似文献
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利用化学键方法寻找新型光学晶体 总被引:1,自引:1,他引:1
利用化学键的观点定量地研究了一些具有各种晶体结构实用材料的介电性质。采用已建立的化学键方法,分析了这些晶体的介电性质与其组成化学键之间的关系。更进一步,基于晶体的化学键方法提出了一个组合方法用于定量确定具有相似晶体结构材料的介电性质。从目前的工作中可以推导出光学晶体非线性起源的结构信息,因此可以在一定程度上帮助人们开展非线性光学晶体工程的研究工作。 相似文献
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《Progress in Crystal Growth and Characterization of Materials》2020,66(2):100484
This paper reviews advancements and some novel ideas (not yet covered by reviews and monographs) concerning thermodynamics and kinetics of protein crystal nucleation and growth, as well as some outcomes resulting therefrom. By accounting the role of physical and biochemical factors, the paper aims to present a comprehensive (rather than complete) review of recent studies and efforts to elucidate the protein crystallization process. Thermodynamic rules that govern both protein and small-molecule crystallization are considered firstly. The thermodynamically substantiated EBDE method (meaning equilibration between the cohesive energy which maintains the integrity of a crystalline cluster and the destructive energies tending to tear-up it) determines the supersaturation dependent size of stable nuclei (i.e., nuclei that are doomed to grow). The size of the stable nucleus is worth-considering because it is exactly related to the size of the critical crystal nucleus, and permits calculation of the latter. Besides, merely stable nuclei grow to visible crystals, and are detected experimentally. EBDE is applied for considering protein crystal nucleation in pores and hydrophobicity assisted protein crystallization. The logistic functional kinetics of nucleation (expressed as nuclei number density vs. nucleation time) explains quantitatively important aspects of the crystallization process, such as supersaturation dependence of crystal nuclei number density at fixed nucleation time and crystal size distribution (CSD) resulting from batch crystallization. It is shown that the CSD is instigated by the crystal nucleation stage, which produces an ogee-curve shaped CSD vs. crystal birth moments. Experimental results confirm both the logistic functional nucleation kinetics and the calculated CSD. And even though Ostwald ripening modifies the latter (because the smallest crystals dissolve rendering material for the growth of larger crystals), CSD during this terminal crystallization stage retains some traces of the CSD shape inherited from the nucleation stage. Another objective of this paper is to point-out some biochemical aspects of the protein crystallization, such as bond selection mechanism (BSM) of protein crystal nucleation and growth and the effect of electric fields exerted on the process. Finally, an in-silico study on crystal polymorph selection is reviewed. 相似文献
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D. A. Chareev 《Crystallography Reports》2016,61(3):506-511
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. 相似文献
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《Journal of Crystal Growth》2006,286(1):108-113
The bond valence model is employed to calculate the bond strength of constituent chemical bonds formed between growth units in both potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) crystals, with the aim to predict and control the crystal shape. After calculating and comparing the relative growth rates of all selected planes, which are related to the crystallographic structure and chemical bond strength, the natural morphology of both KDP and ADP can be conveniently deduced. To check the calculated results, the crystallites of KDP and ADP are grown under different growth conditions; their morphologies accord well with our theoretical calculations. Meanwhile, the influence of ethanol anti-solvent on crystal morphology is microscopically interpreted, which alters the crystal morphology by changing the supersaturation of the growing solution and influencing the bonding process. When ethanol is added into the growing solution, the crystal shape becomes slender. 相似文献
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In order to obtain larger NaA zeolite crystals, the influence of starting materials and preparation conditions on the crystal growth has been studied. It is shown that the growth of NaA is most sensitive to changes in the gel composition. The crystal sizes are limited by subsequent nucleation occurring during the crystallization process. At the optimum gel composition, it is possible to grow crystals up to 75 μm in 100–400 ml reactants. 相似文献