钨酸盐晶体中负离子配位多面体的结晶方位与晶体的形貌

钨酸盐类晶体是重要的闪烁晶体．本文从钨酸盐类晶体中负离子配位多面体的结晶方位和相互联结的稳定性出发，探讨了钨酸盐类晶体中[WO4]2-等负离子配位多面体的结晶方位与晶体结晶形貌之间的关系；认为[WO4]2-四面体与金属阳离子（Ca2＋，Pb2＋，Zn2＋）结合时，由于晶体结构和生长条件（如籽晶取向等）的不同，在晶体各族晶面上的叠合速率和结构取向不同，晶体的结晶形貌迥然有别；四面体的面和梭的法线（L2）所对向的晶面，生长速率慢，顽强显露，均属晶体的板面；四面体的顶角所指向的晶面，生长速率快，显露面积小，经常消失．由此可以合理解释钨酸铅等闪烁晶体的生长特征．最后对ABO4型晶体的结构及习性特征进行了总结归纳．     

硫酸盐类晶体中[SO4]2-四面体的结晶方位与晶体的形貌

本文从硫酸盐类晶体中负离子配位多面体的结和相互联结的稳定性出发，探讨了硫酸在晶体中「ＳＯ４」＾２－结晶方位与晶体结晶形貌之间的关系；认为「ＳＯ４」＾２－四面体与金属阳离子结合时，由于晶体结构和生长条件（如温度、过饱和度等）的不同，在晶体各族晶面上的叠合速率和取向不同，晶体的结晶形貌迥然有别。晶体的结晶形貌与「ＳＯ４」＾２－四面体在晶体中的结晶方位一密切相关，四面体的面和棱的法线（Ｌ＾２）所对向的对     

硫酸盐类晶体中[SO_4]~(2-)四面体的结晶方位与晶体的形貌

本文从硫酸盐类晶体中负离子配位多面体的结晶方位和相互联结的稳定性出发，探讨了硫酸盐类晶体中[SO4]2-结晶方位与晶体结晶形貌之间的关系;认为[SO4]2-四面体与金属阳离子（Ba2 、Ca2 、Mg2 …）结合时，由于晶体结构和生长条件（如温度、过饱和度等）的不同，在晶体各族晶面上的叠合速率和取向不同;晶体的结晶形貌迥然有别.晶体的结晶形貌与[SO4]2-四面体在晶体中的结晶方位密切相关，四面体的面和棱的法线（L2）所对向的晶面，生长速率慢，顽强显露，均属晶体的板面;四面体的顶角所指向的晶面，生长速率快，显露面积小，经常消失.     

若干晶体结晶习性的形成机理

本文根据在热液条件下生长水晶和钛酸钠晶体的电泳实验，提出热液条件下，上述晶体的生长基元具有负离子配位多面体的结构形式。由于溶液过饱和度在变化，这些生长基元的维度也随之变化。不同维度的生长基元往晶体各族晶面上叠合速率的比例也发生相应改变。它直接反映在晶体结晶形貌上。本文根据不同维度生长基元在各族晶面上的叠合速率解释了水晶和钛酸钠的结晶习性形成机理。     

磷酸盐晶体中络阴离子结晶方位与晶体形态

研究了磷酸盐类晶体中的络阴离子[PO4]-和[CaP6O24]16-在晶体中的结晶方位,与[ClCa6]11 八面体相互联结的稳定性决定了各个面族的生长速率.根据磷灰石各族晶面显露的习性,提出了采用人工生长的磷灰石做人工关节时,应该注意磷灰石的取向问题．平行于C轴方向生长的磷灰石有利于与人体骨骼的快速愈合．     

结晶温度对左旋聚乳酸的晶体改性和晶体形貌的影响

以左旋聚乳酸(PLLA)为原料,制备了无定型PLLA膜及无定型PLLA在不同温度下等温结晶的样品。利用红外光谱(FT-IR)、X射线衍射(XRD)和偏光显微镜(POM)分析了结晶温度的改变对PLLA样品的晶体改性及晶体形貌的影响。研究结果表明,结晶温度的改变对PLLA样品的晶体结构、晶型转变及晶粒形貌特征产生了较大的影响。当结晶温度低于100℃时,PLLA主要以无序的α’-晶型存在;随着结晶温度的增加,PLLA的晶体结构和晶型开始转变,当结晶温度超过120℃后,PLLA主要以α-晶型的形式存在;而当结晶温度在100～120℃范围内,则形成的是α’-与α-晶型PLLA的混合形式存在。另一方面,POM照片测试结果表明,随着结晶温度的升高,PLLA的晶体形貌发生了改变,晶粒尺寸随温度的增加而增加,结晶速度增加,晶粒数量减少,PLLA晶体由α’-向α-晶型发生了转变。     

碘化汞(α-HgI_2)晶体气相生长中的形貌转变研究

采用高纯HgI_2多晶原料,利用改进的静态升华法生长了α-HgI_2晶体.生长15天的晶体生长界面呈小平面,而生长29天的晶体生长界面呈椭圆形,表明α-HgI_2晶体气相生长中存在生长形貌转变的现象.形貌转变的原因可能是自由碘在生长界面富集和不同晶面生长速率差异所致.生长29天的晶体体积约为1.3cm~3,可能达到了该条件下的最大体积.     

超声在工业结晶的应用

超声在结晶过程中的应用,近几年引起了国内外学者的广泛兴趣,主要探讨超声对结晶过程中结晶溶液的诱导期、溶液的一次成核、二次成核、晶体的结晶速率以及晶体的形貌和结构的影响.发现超声可以缩短诱导期,加速晶核的生成.提高晶体的结晶速率,改变晶体的形貌.特别是对产品的影响,可以更好地满足人们对产品的要求.     

简立方晶体（001）晶面生长的蒙特卡罗模拟

通过对简立方晶体(001)晶面生长的蒙特卡罗模拟,获得了不同晶体表面热粗糙度,不同过饱和度,不同平均扩散距离以及不同表面尺寸下晶体生长速率;同时,应用舍维数法,计算了表面分形维数;并对表面形貌及描述表面特性的相关参量作了分析.结果表明,法向生长模式和二维核生长模式,包括单核和多核生长模式,都可能出现,其主要取决于热粗糙度和过饱和度的大小.晶体生长速率与表面的微观特性紧密相关,如扭折、台阶、台面和吸附基元的百分比.     

TiO2和α-Al2O3晶体的生长习性

通过水热法制备粉体的实验观察到金红石、锐钛矿和α－Ａｌ２Ｏ３晶体的生长习性,采用配位多面体生长习性法则合理地解释了ＴｉＯ２和α－Ａｌ２Ｏ３的生长习性,其主要结果为α－Ａｌ２Ｏ３晶体的生长飞快生为平板｛０００１｝,其各晶面的生长速度为：Ｖ｛０００１｝〈Ｖ｛１１２３｝〈Ｖ｛０１１２｝＝Ｖ｛１１２０｝〈Ｖ｛０１１０｝;金红石的生长习性为柱状,其各晶面的生长速度为;Ｖ〈１１０〉〈Ｖ〈１００〉〈Ｖ〈１０１〉     

Morphology, Growth Process and Symmetry of {0001} Face on Yb：YAl3（BO3）4 Crystal

The {0001} face develops on the habit of self-frequency doubling laser crystal Yb: YAl3(BO3)4 (YbYAB) only under high growth rate condition, and its morphology is rough. To study the growth mechanism of {0001} face, we have observed the growth morphology on {0001} polishing section by atomic force microscopy (AFM). A series of AFM images captured in different growth durations on the {0001} polishing section reflect the crystal growth process. It is shown that the growth morphology on the {0001} polishing section was rough with many hillocks at the first growth stage, and it can become smooth finally, although the growth morphology on the {0001} face develoFed naturally on YbYAB crystal habit is always rough. On the smooth {0001} surface formed at the last growth stage, there aresome triangular pits. This fact is different from that of hillocks in most crystal growth morphologies. AFM can easilydistinguish the pits or hillocks on the surface, but differential interfere contrast microscopy (DIC) can not do. Theorientation of the triangular pits is just the opposite to the triangular {0001} faces. The chemical etching patternis also composed of this kind of triangular pits. These growth morphology and etching pattern of the {0001} facesshow 3m symmetry, but the point group of YbYAB crystal is 32. The symmetric contradiction between morphologyand point group does not exist for quartz, although whichsurface morphology we can distinguish the right form ormorphology we can not do. The reason for the symmetricand its point group is not known yet.has the same point group as YbYAB. From quartz {0001}left form of the crystal, but from YbYAB {0001} surfacecontradiction between YbYAB {0001} surface morphology and its point group is not known yet.     

非完整形态KH2PO4晶体薄表面层生长特性

实时观察了非完整形态的KH2PO4 (KDP)晶体在过饱和溶液中以薄表面层生长形式恢复其结晶学形态的过程.提出了晶体形态恢复的“最小多面体原理”,即:在自由生长系统中,对于非完整形态的KDP晶体,当其以薄表面层形式恢复其结晶学完整形态时,薄表面层将选择相应的奇异面方向生长,使晶体形态最终恢复为一个由各结晶学显露面所围成的体积最小的凸多面体.利用PBC理论分析了生长基元在非结晶学显露面上的附着情况并阐述了锥顶处薄表面层倒垂生长的原因.结果表明,薄表面层形成与晶体非完整结晶学形态及不均匀水动力学条件相关联.柱面凹角与非正常棱边及Z切片正常棱角均可诱发产生薄表面层,且薄表面层生长终止于其所在奇异面的正常结晶学晶棱.     

TiO2和O-Al2O3晶体的生长习性

通过水热法制备粉体的实验观察到金红石、锐钛矿和α-Al2O3晶体的生长习性．采用配位多面体生长习性法则合理地解释了Ti O2和α-Al2O3的生长习性．其主要结果为α-Al2O3晶体的生长习性为平板{0001}，其各晶面的生长速度为：V｛0001 }＜V｛1123}；锐钛矿的生长习性为四面体，其各晶面的生长速度为V<010>=V<001>>V<010>>V<111>．而PBC理论很难合理地解释α-Al2 O3晶体的生长习性．     

电流密度对甲基磺酸盐电沉积亚光锡的影响

在甲基磺酸盐电镀溶液中进行恒电流电沉积亚光锡镀层实验,考察电流密度对镀液极化性能、阴极过电位、电流效率、沉积速率及镀液分散能力的影响。利用SEM和XRD分析不同电流密度所得锡镀层的表面形貌和结晶取向。结果表明:随着电流密度增大(0.5～4A.dm-2),镀液的阴极极化增大,电流效率先增加后降低,沉积速率不断加快,但镀液分散能力有所下降;晶体由"向上生长"模式逐渐转变为"侧向生长"模式,择优取向由(321),(431)晶面转变为(112),(332)晶面;添加剂吸附在晶体表面,降低了被吸附晶面的表面自由能,使这些晶面的生长速率下降,从而改变了镀层择优取向和晶体生长的方式。     

Crystallographic orientation and temperature effects on the fatigue crack growth rate and resulting fracture surface morphology in PWA1484 single crystal superalloy

This research looked at the effect of crystallographic orientation and temperature on the fatigue crack growth rate and the resulting fracture surface morphology in PWA1484 single crystal superalloy. Two groups of single edge notch tension specimens, one group with controlled secondary orientations and one group with uncontrolled secondary orientation, were tested at temperatures from 649°C to 982°C at R‐ratios of 0.1 and 0.7. It was found that the effect of temperature on the crack growth rate becomes more pronounced as the crack driving force increases while the secondary orientation and R‐ratio effects on the crack growth rate increase with increasing temperature. Two types of crack surface morphology were seen during fractography. The first was a precipitate avoidance (γ′ avoidance) morphology that was rolling but still predominantly flat when observed on a larger scale. In <001> primary oriented specimens, this fracture mode tended to follow the precipitate/matrix faces (microscopically cubic) while macroscopically staying essentially normal to the applied loads. The second mode was a form of cleavage (γ′ shearing) and occurred predominantly on octahedral crystallographic planes.     

A novel growth method for organic nonlinear optical crystals

A novel crystal growth method called seed-orientated undercooled melt growth is proposed for growth of organic nonlinear optical (NLO) crystals. The main advantage of this method is that organic NLO crystals can be grown along a given direction and the optional crystal faces (h k l) may be grown directly in a crystallizer. The grown crystals with determinate crystal faces are possible to apply as nonlinear optical devices regardless of subsequent cutting and polishing. Using this method, the different crystal faces of benzophenone crystals were successfully grown in a quartz crystallizer, and the orientation of the grown crystal faces were measured by an X-ray angular instrument.     

Anisotropic Strain Relaxation of Graphene by Corrugation on Copper Crystal Surfaces

Corrugation is a ubiquitous phenomenon for graphene grown on metal substrates by chemical vapor deposition, which greatly affects the electrical, mechanical, and chemical properties. Recent years have witnessed great progress in controlled growth of large graphene single crystals; however, the issue of surface roughness is far from being addressed. Here, the corrugation at the interface of copper (Cu) and graphene, including Cu step bunches (CuSB) and graphene wrinkles, are investigated and ascribed to the anisotropic strain relaxation. It is found that the corrugation is strongly dependent on Cu crystallographic orientations, specifically, the packed density and anisotropic atomic configuration. Dense Cu step bunches are prone to form on loose packed faces due to the instability of surface dynamics. On an anisotropic Cu crystal surface, Cu step bunches and graphene wrinkles are formed in two perpendicular directions to release the anisotropic interfacial stress, as revealed by morphology imaging and vibrational analysis. Cu(111) is a suitable crystal face for growth of ultraflat graphene with roughness as low as 0.20 nm. It is believed the findings will contribute to clarifying the interplay between graphene and Cu crystal faces, and reducing surface roughness of graphene by engineering the crystallographic orientation of Cu substrates.     

Ti-40Al-2B合金微观组织和初生TiB2生长特征

用原位自生法制备了Ti-40Al-2B(wt%)复合材料,并用XRD、SEM对复合材料的相组成和微观组织,特别是TiB₂的形貌进行了研究。结果表明:该合金由TiAl和TiB₂两相组成。其中TiB₂颗粒以初生的块状和共晶的片状或细棒状形式共存。初生TiB₂呈六面棱柱体,端面有清晰的生长台阶,其显露晶面分别为(0001)和｛101 - 0｝。结合晶体生长理论分析认为:TiB₂的生长单元为一个硼原子和六个钛原子组成的三棱柱,硼原子位于三棱柱的中心,生长方式以台阶式生长为主。其中｛112 - 1｝面生长速率最快,｛101 - 0｝面生长速率最慢,导致TiB₂形成以｛101 - 0｝面为棱柱面的六面棱柱结构。