Growth of KTiOPO<Subscript>4</Subscript> crystals doped with zinc and studies of their physical properties and specific structural features

A series of potassium titanyl phosphate single crystals doped with zinc (KTP: Zn) is grown by spontaneous flux crystallization. Their properties and the way the additive is implanted in the crystal lattice are studied. The inclusion of zinc atoms in the KTP structure is evidenced by the data of chemical analysis and the results of studies of electrophysical properties (the growth of conductivity and increase of relaxation anomalies). Precision X-ray diffraction studies of KTP: Zn single crystals reveal changes in the channel of the structure which correlate with the physical properties of this crystal series. No substitution of zinc atoms for titanium, phosphorus, or potassium atoms is found in the structure. Zinc atoms can be located at structural defects, domain walls, and the crystal surface.     

A model study of the growth of crystals consisting of a small number of metal atoms by the Hückel molecular orbital method (I). Addition of One atom to small crystals

The paper deals 1) with the regularities of the formation of (N + 1)-atomic clusters during the growth of N-atomic one-, two-, and three-dimensional crystals and 2) with the distribution with respect to stability of the (N + 1)-atomic clusters. The N-atomic crystals have the structure of a hypothetical metal with a simple cubic lattice and a small number of one-electron atoms. The binding energy (BE) of the clusters calculated by the Hückel molecular orbital method was assumed to be a measure of their stability. Interactions between nearest-neighbours only were taken into account. The most stable (N + 1)-atomic cluster formed from a one-dimensional crystal is that in which the N + 1-st atom is bonded to the end atom of the N-atomic one-dimensional crystal. For two-dimensional crystals, the N + 1st atom forms the strongest bond with an atom from the diagonal of the square. With three-dimensional crystals, the N + 1st atom is most strongly bonded to a corner atom of the small crystal. The inhomogeneity in the bond energy of the N + 1st atom to a surface atom of the small N-atomic crystal decreases with increasing N. According to earlier studies of ours, the BE per atom increases, whereas the mean energy of a nearest-neighbour bond decreases with increasing N.     

以磷化铁为添加剂沿(111)面生长磷掺杂金刚石大单晶

掺杂是调控金刚石性能的一种重要手段。本文采用温度梯度法,在5.6 GPa、1 312 ℃的条件下,选用Fe₃P作为磷源进行磷掺杂金刚石大单晶的合成。金刚石样品的显微光学照片表明,随着Fe₃P添加比例的增加,金刚石晶体的颜色逐渐变深,包裹体数量逐渐增加,晶形由板状转变为塔状直至骸晶。金刚石晶形的变化表明Fe₃P的添加使生长金刚石的V形区向右偏移,这是Fe₃P改变触媒特性的缘故。红外光谱分析表明,Fe₃P的添加使金刚石晶体中氮含量上升,这说明磷的进入诱使氮原子更容易进入金刚石晶格中。激光拉曼光谱测试表明,随着Fe₃P添加比例的增加,所合成的掺磷金刚石的拉曼峰位变化不大,其半峰全宽(FWHM)值变大,这说明磷的进入使得金刚石晶格畸变增加。XPS测试结果显示,随着Fe₃P添加比例的增加,金刚石晶体中磷相对碳的原子百分含量也会增加,这意味着添加Fe₃P所合成的金刚石晶体中有磷存在。     

晶体生长时的固液相结构变化分析

晶体的溶解、熔化以及结晶成核生长时的固液相原子结构是怎样变化的,晶体生长时的生长基元是原子还是原子团.本文根据各种材料液相结构的最新研究结果,提出不饱和配位结构转换模式,并以此模式对各种常见晶体材料从溶解、熔化到结晶生长时的液态母相结构变化以及晶体成核过程进行了描述和分析,认为晶体生长时的界面结构和液相结构十分接近,溶解、熔化主要是晶体表面的不饱和配位原子(离子)转换到液相结构的过程,晶体生长主要是液相中的不饱和配位原子(离子)转换到固液生长界面的位错位置,使配位结构更饱和的过程.随着液相过饱和度的增大,液相结构单元的原子数越来越多,吸附到晶体生长界面若来不及转换回液相,就形成新的位错生长中心,形成晶体生长缺陷.     

Interference pattern of X-ray waves inside the crystal and its image in vacuum in double-field approximation (II)

The energy flows of the X-ray waves, diffracted in thick crystals in double-field approximation, have been examined. It has been demonstrated that in a symmetric Laue case the energy flows in the upper layers are oriented in the direction of incidence and reflection, whereas in the lower layers they are oriented in the direction of the normal to the entrance surface of the crystal. The formation of pendular bands during diffraction of X-rays in thick parallelepiped and wedge-shaped crystals has been investigated. A method for obtaining pendular bands from such crystals is described.     

LGAS晶体的微结构及声表面波特性研究

本文采用第一性原理计算了La3Ga5-xSiAlxO14 (LGAS)压电晶体几何结构、能带和态密度.并研究了其在X、Y和Z切型的声表面波速度、机电耦合系数及能流角.当x=0.5时,构建了La3Ga4.5SiAl0.5O14晶体的1×1×2超晶胞结构,发现A1原子替代2d四面体位置的Ga原子时体系总能量最低,体积最小,因此是最稳定的状态.与石英相比,LGAS具有声表面波速度较低、机电耦合系数较大且存在能流角为零的切型等优点.掺Al元素降低了成本但对结构和声表面波特性影响不大.Y切0是较好的切型,可用于制备声表面波器件.     

Spontaneous crystallization of potassium chloride from aqueous and aqueous‐ethanol solutions; Part 3: Model of the crystallization process

A model of spontaneous crystallization process was proposed. The model describes kinetics of the crystallization process after the end of the induction period. To test the model the published earlier data on crystallization and aggregation kinetics of potassium chloride at its spontaneous crystallization from supersaturated aqueous and aqueous‐ethanol solutions were used. It was found excellent coincidence of the experimental and theoretical data on concentration of the salt and the total number of crystals in solution at crystallization. Somewhat change for the worse was at the theoretical calculations of crystal size distribution at the end of the crystallization process. It indicated that the ways of calculation of size of crystals and their weight fraction in deposit were very approximate. The model allows predicting with satisfactory accuracy kinetics of crystallization using such general parameters of potassium chloride as the specific surface energy and the height of the nucleus‐bridges between crystals at coalescence. It needs further test of the model for other salts. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural reasons for the nonlinear optical properties of KTi<Subscript>0.96</Subscript>Zr<Subscript>0.04</Subscript>OPO<Subscript>4</Subscript> single crystals

This paper reports on the results of the precision X-ray structural investigations of KTi_0.96Zr_0.04OPO₄ single crystals at room temperature. It is established that the incorporation of zirconium atoms into the structure of KTiOPO₄ (KTP) crystals does not lead to substantial changes in the framework structure and results only in an insignificant decrease in the scatter of the distances in the PO₄ tetrahedra and the formation of more symmetric (TiZr)O₆ octahedra as compared to the TiO₆ octahedra. However, the incorporation of zirconium atoms into the KTP structure is accompanied by the redistribution of the electron density in the crystal as a whole, so that the electron density increases in the region of the positions occupied by the potassium atoms. This changes the nonlinear optical properties of the given series of crystals, which are estimated from the intensity of the second harmonic generation signals.     

Mechanism of aggregation and intergrowth of crystals during bulk crystallization from solutions

Available literature data on aggregation kinetics of crystals of a number of salts during their bulk crystallization from solutions have been analysed. The proposed earlier mechanism of aggregation and intergrowth of crystals during bulk crystallization owing to formation of nucleus‐bridges between crystals was tested and confirmed. The aggregation kinetics of crystals was described by the familiar Smoluchowski equation for coagulation of colloidal particles. However, in a bulk crystallization process, the aggregation constant in this equation decreased as supersaturation in a solution lowered. An expression for the aggregation constant in this equation was proposed. The proposed mechanism of crystal intergrowth duringt bulk crystallization allowed evaluating the specific surface energy of tested salts, which turned out to be in reasonable agreement with published literature data. It was concluded that the intergrowth of crystals during bulk crystallization from solutions proceeded via formation of nucleus‐bridges between crystals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and characterization of Au3+ ion irradiated 2-amino-5-nitropyridinium hydrogen oxalate (2A5NPHO)

2-amino-5-nitropyridinium hydrogen oxalate (2A5NPHO) was grown using slow evaporation and bulk crystal of 2A5NPHO was harvested from Assembled Temperature Reduction (ATR) method. Cut and polished crystal was irradiated using Au³⁺ ion with various fluences. Electronic loss, nuclear energy loss and penetration depth were calculated using SRIM software. It was observed in X- ray pattern that intensity of peak was reduced. Intensity of peak decreased with increase of ion fluencies from 10¹³ ions/cm² to 10¹⁴ ions/cm². Optical properties were measured using UV-Vis spectrometer. The increase of absorption was due to excited electrons which were formed by vacancies and formation of additional defects centres. Energy band gap of irradiated crystals increased with increase of ion fluence. Energy band gap of irradiated crystals were 3.39 eV, 3.42 eV, and 3.4 eV for 10¹³ ions/cm², 5 × 10¹³ ions/cm² and 10¹⁴ ions/cm² respectively and increase of band gap was due to the increase of forbidden gap. Microhardness was calculated using Vicker's Hardness tester. Increase of microhardness in irradiation crystal was due to increase of high density lattice defects produced by Au³⁺ of 10.8 MeV. Electrical property was calculated using dielectric constant. Increase of dielectric constant was due to large polarization which caused by disorderness and rich defects in the crystalline surface. Decrease of intensity peak in fluorescence was due to transition of excited electron to intermediated energy levels from excited state which converted into vibrational energy of lattice atoms (phonon). Morphology of irradiated crystal was seen using scanning electron microscope (SEM). It was observed from the SEM image that surface of crystal was heavily damaged. It was also noticed that the thermal stability of the irradiated single crystal increased with increase of ion fluences. Impedance of irradiated crystal was measured. The bulk resistance and grain boundary resistance also were calculated.     

Shape Transformation of Plastic Crystals under the Effect of Surface Energy. Adamantane in Temperature Gradient Conditions

The spontaneous transformation of a polycrystal into a single crystal at high temperatures is observed with adamantane samples. Since the plastic crystal phase at such temperatures is not elastically strained it is concluded that the process is due to the surplus of surface energy in the system. The spontaneous transformation to the equilibrium form of crystals under temperature gradient conditions is investigated. The effect is established both of the surface energy and the shape of the isothermic surfaces.     

Yb∶YAl3(BO3)4晶体形貌与生长速度的关系

观察测量了不同生长速度(相应于不同降温速度)自发成核生长的Yb∶YAl3(BO3)4晶体形貌。粒度较大(>2mm)的晶体不管降温速度快慢形态都很简单,只发育六方柱｛1120｝和菱面体｛1011｝;粒度较小(<2mm)的晶体形态随降温速度增快而变复杂,发育一些罕见的高指数晶面。说明在生长速度较快的条件下,在晶体生长早期,一些高能面发育,在晶体生长后期已尖灭了,晶体生长的大部分时间是在低能面｛1120｝和｛1011｝上进行的。对比了不同生长条件下晶面的粗糙度,随着降温速度的增快,六方柱面｛1120｝和菱面体面｛1011｝由光滑变粗糙,顶面｛0001｝永远是粗糙的。从晶体结构上定性地探讨了3种晶面的杰克逊因子α及生长机理     

人造含硼金刚石单晶表面形貌与生长机制研究

本文借助Olympus光学显微镜、扫描电子显微镜(SEM)和原子力显微镜(AFM)对高温高压合成的含硼金刚石单晶表面形貌进行了分析.研究发现,含硼金刚石表面存在蚀坑、球形颗粒集团、平行台阶、花瓣状生长丘和三角形螺旋台阶等多种表面形貌.这些形貌与晶体内部的缺陷有关,硼原子的进入使金刚石晶体生长速度增加,位错增多,进而导致不同表面形貌的形成,螺旋位错生长是含硼金刚石的主要生长方式.     

Nonstoichiometry and nanocrystallization of silicon-rich silicon carbide deposited by chemical vapor deposition

Silicon carbide (SiC) deposited by chemical vapor deposition (CVD) from methyltrichlorosilane (MTS)/H₂ was often found to be silicon-rich and micro- or nanocrystalline. We address here the question whether the excess silicon would be localized inside the small SiC crystals contained in the deposit or not. We performed semi-empirical total energy calculations and free energy estimations which show that excess Si atoms should not be localized inside a finite SiC crystal. This is essentially due to the difference between the Si---Si and Si---C σ overlaps of sp³ hybrids for a given nearest-neighbor distance. Comparison of a crystallographic equation with experimental results from CVD materials suggests that the SiC nanocrystals be of maximum size allowing all excess Si atoms to be localized at the border of the crystals, provided that there are no Si crystals in the deposited material.     

High-Pressure X-ray Diffraction Studies on Organic Crystals

The high-pressure X-ray diffraction technique, commonly applied for inorganic crystals, is discussed in a view of its application for laboratory studies on molecular crystals of organic compounds – particularly when the weak X-ray scattering of such specimens causes experimental difficulties. To minimize the background-to-signal ratio, relatively big crystal samples (ca. 0.005 A³) were used and the mechanical properties of the gasket material were applied to obtain the optimum experimental conditions for pressure generation and lowering the background of reflections. The mechanical properties of tungsten, Inconel, and hardened steel gaskets are different and these properties can be helpful in planning high-pressure measurements with large high-pressure chamber to contain a big crystal sample. Several characteristic features of organic crystals – like their strong compressibility (depending on the nature of intermolecular interactions) and pressure-dependence of thermal vibrations of atoms – can have a direct impact on the conditions of high-pressure experiments. The properties of molecular crystals of organic compounds have been discussed on the basis of several high-pressure structural studies, mainly on simple cyclic β-diketoalkanes (enol forms). It has been attempted to assess the feasibility of investigating the details of molecular structure at high pressures by X-ray laboratory studies. A systematic pressure-induced change in the length of double C  O bonds is observed in this group of compounds, which can be correlated with the compression of the H-bonds involving the carbonyl groups.     

Modern possibilities for calculating some properties of molecules and crystals from the experimental electron density

Methods for calculating some properties of molecules and crystals from the electron density reconstructed from a precise X-ray diffraction experiment using the multipole model are considered. These properties include, on the one hand, the characteristics of the electron density and the inner-crystal electrostatic field and, on the other hand, the local electronic energies (kinetic, potential, total), the exchange energy density, the electron-pair localization function, the localized-orbital locator, the effective crystal potential, and others. It is shown that the integration of these characteristics over pseudoatomic volumes bounded by the surfaces of the zero flux of the electron density gradient makes it possible to characterize directly from an experiment the properties of molecules and crystals in terms of the atomic contributions. The computer program WinXPRO2004, realizing these possibilities, is briefly described.     

SiC籽晶表面状态对晶体质量的影响

为了研究表面状态对晶体质量的影响,本文分别采用腐蚀后抛光与未抛光的晶片作为籽晶,利用金相显微镜对所得晶体进行了显微观察,结果表明:经过腐蚀后抛光的籽晶生长出的晶体质量高于未抛光籽晶所得晶体;生长前端的位错尺寸以及数量小于未抛光籽晶,说明抛光去除了部分表面浅的缺陷腐蚀坑,同时减小深腐蚀坑的尺寸,使得籽晶生长表面的缺陷密度和尺寸大大降低,有助于减少后期生长的晶体中的缺陷密度,提高结晶质量.     

掺杂对GaN晶体力学性能影响的研究

对GaN单晶力学性能的研究有助于解决其在生长、加工和器件应用中的开裂问题。本文围绕掺杂对GaN单晶力学性能的影响,通过纳米压痕法测试了不同掺杂类型(非掺、Si掺和Fe掺)GaN单晶的弹性模量和硬度,测试结果表明掺杂对GaN单晶的硬度有重要影响。Si掺、Fe掺GaN较非掺样品硬度有所提升,用重掺杂的氨热GaN单晶作为对照,也证明了这一结论。通过高分辨X射线衍射分析和原子力显微镜表征实验发现,晶体结晶质量、接触面积等因素对GaN单晶硬度的影响较小。对GaN表面纳米压痕滑移带长度和晶体晶格常数进行测试,结果表明,掺杂影响GaN单晶硬度的主要原因是缺陷对GaN位错增殖、滑移的阻碍作用和掺杂引起的GaN晶格常数的变化。     

Polyhedral stability ‐ on the growth of flat crystal faces on small molecule and protein crystals

The old standing problem of face morphology is discussed. A special emphasis is put on the macroscopically flat faces, appearing on small molecule crystals mostly during calm growth, under low supersaturations. As distinct, protein crystals are growing with macroscopically flat faces even under surprisingly high supersaturations. Explanations of these facts are suggested by considering the surface micro‐profile of crystal faces which growth is driven by screw dislocations. It is shown that, due to kinetic reasons, the tips of the growth hillocks and the valley between them have to be levelled to some extent (at least on a quasi‐atomic scale) under low enough supersaturations. The amplitude of the surface roughness has to be suppressed also due to the surface energy gain, especially under quasi‐equilibrium. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Kinetics of crystallization in binary solutions

A two-dimensional nucleation is required to grow the crystals of low energy planes. Expressions for the size and free energy of the two-dimensional nucleus corresponding to a saddle point in binary system are derived. The concentration of the critical nuclei in the system is related to the critical free energy of the two-dimensional nucleus. A circular island of atoms on the growing surface is considered and the flux of atoms on the surface going to the growing walls of the island from either direction is calculated. The rate of advance of the curved step is determined and hence the velocity of the straight step in the A-B crystal-binary solution interface is found.