共查询到17条相似文献,搜索用时 187 毫秒
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本文用负离子配位多面体生长基元理论模型讨论了多型性晶体表面螺旋结构的形成,提出在多型性晶体中配位多面体呈层状分布,配位多面体的面为层的边界,上、下层负离子配位多面体不是呈镜象对称的,在三方晶系和六方晶系的晶体中是沿晶轴a、b错开,上、下两层负离子配位多面体体呈交叉对应,从而达到稳定平衡.晶轴c与负离子配位多面体高次对称轴平行,配位多面体往界面叠合是绕着c轴转动的,其叠合轨迹为螺旋或同心环结构.从多型性晶体螺旋结构的规律性可以看出,晶体生长基元为负离子配位多面体,由于负离子配位多面体的面与呈现螺旋结构的晶面平行,所以生长速率慢,是一个显露面积大的稳态面.螺旋结构只是在该面族上显露. 相似文献
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负离子配位多面体生长基元与晶体表面结构(Ⅲ):多型性晶体表面螺旋结构的形成:碳化硅(SiC) 、石墨(C)、云母[KMg3(A1Si3O10)](OH,F)2,碘化镉(CdI2)、氯化镉(CdCl2) 总被引:2,自引:1,他引:1
本文用负离子配位多面体生长基元理论模型讨论了多型性晶体表面螺旋结构的形成,提出在多型性晶体中配位多面体呈层状分布,配位多面体的面为层的边界,上,下层负离子配位多面体不是镜象对称的,在三方晶系和六方晶系的晶体中是沿晶轴a,b错开,上,下两层负离子配位多面体体呈交叉对应,从而达到稳定平衡。晶轴c与负离子配位多面体高次对称轴平行,配位多面体往界面叠合是绕着c轴转动的,其叠加轨迹为螺旋或同心环结构。从多型性晶体螺旋结构的规律性可以看出,晶体生长基元为负离子配位多面体,由于负离子配位多面体的面与呈现螺旋结构的晶面平行,所以生长速度慢,是一个显露面积大的稳态面。螺旋结构只是在该面族上显露。 相似文献
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BaY2F8晶体生长基元与结晶机理的探讨 总被引:1,自引:0,他引:1
本文通过对BaY2F8晶体结构的分析,从晶体的生长基元为负离子配位多面体理论出发,对自然冷却条件下BaY2F8晶体自发结晶习性进行了研究,提出了以Ba2+为中心的近八配位十二面体和以Y3+为中心的近八配位十二面体是晶体生长的基元.并根据自发结晶的BaY2F8的XRD,说明了BaY2F8晶体的{200}、{130}、{021}、{330}、{-111}、{111}、{221}、{002}等面族比较发育的原因.本文证实了仲维卓的负离子配位多面体理论对BaY2F8晶体生长的适用性,并对探索新的BaY2F8单晶生长方法有参考作用. 相似文献
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从负离子配位多面体生长基元模型出发,根据大维度生长基元的结构特性,讨论了人工可控氢氧化镁晶须生长,主要介绍了多元醇法及镁盐过饱和度法.多元醇法的实质是醇中的羟基在一定条件下与大维度生长基元中的羟基发生假联结(即吸附),使得与多元醇发生了假联结的晶面生长速率大大减小或甚至停止生长,而其他晶面仍然保持原有的速率生长以致形成晶须.镁盐过饱和度法就是使得生长基元[Mg-Ax](x-2)-(A≠OH-)的浓度很大,且要远比[Mg-(OH)x](x-2)-组分浓度大4倍以上,以先形成碱式镁盐晶须,碱式镁盐晶须再与适当的碱液反应,即可制备得氢氧化镁晶须. 相似文献
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Heat transfer and fluid flow in HEM crystal growth of silicon in cylindrical cavity is studied numerically. The walls of the crucible are heated to a fixed temperature. The exchanger that causes and induces natural convection is seated at the middle‐bottom of the crucible. The finite‐volume method is employed to solve the governing equations with proper boundary conditions. The effects of transport mechanism on the temperature distribution, melt flow, pressure and stream function are presented. We focus our work on the pressure field which has not yet been studied in HEM crucible. Also, we extend our work on a wide range Grashof number and for large numbers until 1012 not yet studied in HEM furnace. It is found that the onset of flow fluctuations appears at Gr = 1010. Uniform temperature is observed in the entire melt at high Grashof number with development of a thermal boundary layer close to the exchanger. The thermal boundary layer thickness is calculated for strong buoyancy regime. Besides, for very high Gr number, buoyancy has less effect on temperature and then on melt‐crystal interface shape. During enlarging Gr, pressure evolution is related to temperature variation more than flow pattern. 相似文献
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In this paper the effect of the growth temperature fluctuation, for instance, the transient furnace temperature variation due to a short‐term electric power supply interruption on BBO crystal growth was investigated based on the theory of temperature wave transmitting in melt and the boundary layer theory of melt. It was found that the critical width of the temperature pulse to avoid the temperature wave penetrating through the boundary layer and reaching to the growth interface at a constant rotation speed (9∼4 r/min) is 69∼150 s and the corresponding amplitude of the temperature pulse is high more than 60 °C due to the large thickness of the velocity boundary layer of the melt. This result indicates that a small transient temperature fluctuation has no significant effect on the crystal quality, and therefore implies that not only transport processes but interface growth kinetics, a two‐dimensional nucleation growth mode at the interface may also dominate the crystal growth. 相似文献
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X.N. Jiang D. Xu D.R. Yuan M.K. Lu S.Y. Guo G.H. Zhang X.L. Duan 《Crystal Research and Technology》2002,37(1):67-75
To get a better understanding of the growth of cadmium mercury thiocyanate (CMTC), a promising nonlinear optical crystal, we have investigated the structures of its growth solutions by using Raman spectra. It has been found that Hg(II) ions coordinate with SCN‐ through S atoms, forming the most stable complex of [Hg(SCN)4]2‐ in the solutions while Cd(II) ions bind to SCN‐ around Hg(II) through the other end N atom. Thereby, taking [Hg(SCN)4]2‐ anions as centers, a network structure of Cd(II)‐N‐C‐S‐Hg(II) is formed in the solutions as in the crystal lattice. It is notably that there are other complexes, mostly the Cd(SCN)n (n < 4) complexes, in the solutions. Therefore, the solution structure of CMTC is complicated, which is believed to contribute greatly to the difficulty of growing large single crystals. Based on the analysis of the solution structures, the reasonable growth units of CMTC are proposed. 相似文献
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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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N. N. Timoshenko V. I. Goriletskii B. V. Grinev V. I. Sumin O. V. Sizov 《Crystallography Reports》2005,50(1):S92-S96
An attempt is made to establish a correlation between the radial and axial growth rates and the change in the conditions of heat transfer from a growing crystal to the atmosphere of the water-cooled vacuum furnace for the growth of large alkali halide single crystals. It is found experimentally that an increase in the growth rate leads to an increase in the automatic compensation of the melt temperature by the main heater. In this case, the thickness of the layer of melt condensate on the end face and the lateral surface of the crystal decreases. It is revealed that the possibility of growing infinitely long ingots in the presence of intense melt evaporation is restricted by the possibilities of the heat transport through the boundary between the furnace atmosphere and the cooled furnace walls, onto which melt condensate deposits. 相似文献