共查询到20条相似文献,搜索用时 15 毫秒
1.
C. Paorici M. Zha L. Zanotti G. Attolini P. Traldi S. Catinella 《Crystal Research and Technology》1995,30(5):667-675
The vaporisation-condensation scheme of urea has been investigated in the temperature region below the melting point, in order to establish the thermodynamic reactions on which the physical vapour transport (PVT) of urea is based. By making use of both reported data and experimental results of MS, DTA, DTG, and HPLC analysis, it was shown that PVT relevant reactions are basically molecular sublimation and partial decomposition in solid biuret and ammonia. MS analysis of urea crystals and source residues have also shown that no decomposition can be observed in the growing crystals, unless reheated during growth. The temperature dependence of the decomposition pressure has been found to be: log10PNH3 [torr] = 38 – 13840/T [K]. The use of this relation in diffusive mass transport calculations brought to linear growth rate values not in disagreement with the experimental values found in closed tube PVT grown crystals. 相似文献
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Tin diselenide single crystals have been grown by the physical vapour transport (PVT) method. Optical absorption studies give an indirect allowed transition at 1.03 eV at room temperature. The electrical resistivity parallel and perpendicular to c-axis, mobility and carrier concentration have been determined. Dependence of resistivity parallel to c-axis on temperature gives an activation energy of 0.072 eV. Growth spirals observed for the first time on the as grown faces of these crystals are also presented here. 相似文献
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Associate Pro. Zheng-Hui Li Wei-Tang Li Jun Liu Shi-Fu Zhu Bei-Jun Zhao Hong Yuan Hua-Peng Xu 《Crystal Research and Technology》1995,30(5):595-598
The Hgl2 single crystal with shiny natural crystal planes, low density of dislocation, and 350 g in weight has been grown by a new technique of modified vapoir phase located point method. The perfection and nuclear spectroscopic performance of the grown crystals are also studied. 相似文献
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K. Bttcher 《Crystal Research and Technology》2001,36(7):719-728
Steady‐state heat and mass transport at the SiC growth process are computed by the general‐purpose finite‐element package FIDAPTM. Specific features are the radiation exchange in several cavities at temperatures up to 2700 K and concentration dependent Stefan velocities resulting from sublimation/condensation at the vapour‐solid interfaces. The article describes the computational procedure in order to achieve convergence of the temperature and velocity field. The transport rate of the SiC building species meets the range of experimental results. 相似文献
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Takamasa Kaito Shin‐Ichiro Yanagiya Atsushi Mori Tetsuo Inoue 《Crystal Research and Technology》2007,42(7):652-656
In this paper, the vapour transport of PbBr2 under vacuum during vacuum distillation refining and its condensation on the wall of the vessel were described. The macro‐ and micro morphologies of PbBr2 crystals grown in the vessel (glass tube) were studied. The crystal shape changed dramatically depending on the positions of condensation in the vessel, i.e., the crystal shape varied from an isometric polyhedron to columnar crystals with facets, and to a massive crystal without facets with a rise in the wall temperature. These results were interpreted in terms of the concentration gradient of the molecules in the vessel, surface roughening and/or surface melting of the crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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V. V. Volkov C. Van Heurck J. Van Landuyt S. Amelinckx E. G. Zhukov E. S. Polulyak V. M. Novotortsev 《Crystal Research and Technology》1993,28(8):1051-1061
The growth features of FeCr2S4 spinel single crystals prepared by chemical vapour transport were studied by means of scanning electron microscopy, transmission electron microscopy, high resolution electron microscopy, electron diffraction and X-ray analysis. Our results indicate that the epitaxial growth of the new phases FeCr7S12 and FeCr8S12, both based on the NiAs structure, can essentially inhibit the growth of large FeCr2S4 spinel single crystals in the octahedral habit. The new phases are fully characterised and the effects of defect ordering in these new phases are also reported. 相似文献
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采用高纯Zn、Mg、Se2单质为原料,以NH4Cl作为反应输运剂,用化学气相输运(CVT)的方法一步成功生长出ZnMgSe单晶。通过XRD、RO-XRD、EDS、紫外可见分光光度计和光致发光(PL)技术研究了ZnMgSe晶体的结构、成份以及光学特性。结果表明:ZnMgSe单晶具有良好的结晶性能,在400~800 nm范围内透过率达到40%~50%,在2.2~2.6 eV范围内存在与深能级电子复合相关的发光带。研究证明由Zn、Mg、Se2单质在输运剂NH4Cl辅助下一步直接合成ZnMgSe单晶是可行的。 相似文献
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An original apparatus allows the growth of sapphire single crystals with complicated forms. Edge-defined Film-fed Growth (EFG) or Stepanov method, Growth from an Element of Shape (GES) method, as well as imaginative combined variants of those processes are available with this equipment. Related to the growth parameters, the quality of the crystals pulled from the melt is investigated in terms of minor gas bubbles distribution and misorientation. X-ray transmission, optical microscopy together with light transmittance measurements are the tools to make sure of optical applications for those products. 相似文献
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优质立方六面体金刚石大单晶的生长研究 总被引:1,自引:2,他引:1
高温高压静压触媒法合成的金刚石单晶,往往呈现六八面体形貌,因为立方六面体单晶{100}面的生长区间相对较小.本研究利用高温高压温度梯度法,自制Fe-Ni合金触媒,通过对合成组装和工艺进行合理调整后,控制晶体在相对低温适合{100}面生长区域内生长,得到的晶体均呈现完整立方六面体形貌;同时为抑制包裹体和其他杂质的进入,人为的提高晶体的径向平铺生长速度,抑制其轴向生长速度.以在33 h内合成的优质立方六面体晶体为例,晶体最大方向尺寸达到7.3 mm,重1.2克拉,其径向生长速度达到0.22 mm/h,轴向生长速度仅为0.08 mm/h,增重速度为7.3 mg/h. 相似文献
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The growth kinetics of TGS crystals was studied at high supersaturations under the Curie temperature. The kinetics data proved that the crystal growth was mainly controlled by BCF surface diffusion model. The continuous growth was fitted to the growth rate data of (110) face. Its edge energy, Jackson factor, activity energies, kinetic coefficients were calculated. 相似文献
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铌酸锂晶体的生长研究 总被引:2,自引:1,他引:2
近年来,铌酸锂晶体由于其自身所具有的多种优异性能和巨大的应用前景而受到了人们的广泛关注,但生长出满足不同市场要求的高质量铌酸锂单晶体比较困难.本文从晶体生长技术的角度综述了铌酸锂单晶体不同的生长方法以及各自的特点,并分析了在生长铌酸锂晶体时出现的一些问题. 相似文献
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KTi1-xSnxOPO4晶体生长及其物理性质的研究 总被引:1,自引:0,他引:1
采用熔盐法生长了一系列磷酸氧钛锡钾单晶体并测定了其晶体结构和相应的物理性质,发现在该类型晶体中随着四价阳离子Sn对Ti的掺杂替代导致晶胞参数增大,铁电相变温度降低和非线性光学特性减弱,同时发现在居里温度附近,一些晶体出现类似快离子导体特性的电导率跃迁。 相似文献
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采用自发成核方法,以NaCl-Na2CO3为助熔剂,生长了毫米级的NaCo2O4晶体。通过X射线衍射对晶体作了表征。利用扫描电子显微镜和原子力显微镜研究了晶体的形貌和生长机理。结果表明:所得晶体是NaCo2O4,属于六方晶系,晶胞参数:a=b=0.2842 nm,c=1.0894 nm,V=0.0761997 nm3。NaCo2O4晶体是沿c轴层状生长的,同时从阴离子配位多面体的角度分析了晶体的形貌。 相似文献
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K. Joo J. Paitz D. Klimm P. Reiche K.H. Auh W. Schrder 《Crystal Research and Technology》2000,35(4):493-499
Barium cerate crystals of 1.5 mm diameter could be grown from melt solutions containing barium chloride, barium oxide (from thermolysis of barium carbonate), and cerium(IV) oxide. The maximum size of the crystals is limited by the low solubility of cerium(IV) oxide in the barium chloride melt (ca. 0.1 Mol%). The flux can be removed by leaching the melt with water. Acid solutions must not be used to avoid decomposition of the barium cerate crystals. Neither congruent melting or incongruent decomposition of the BaCeO3 crystals could be found up to 1580 degrees centigrade. 相似文献