Etching studies on {100} faces of MgO crystals in H3PO4 acids

The effect of temperature (20–100°C) and concentration of H₃PO₄ etching solutions on the etching behaviour of {100} faces of MgO crystals in investigated. It is observed that the formation of etch pits and pyramids and the values of dissolution rate depend on the etching conditions. The density of the pyramids in 33.08 N H₃PO₄ solution was found to be maximum at 20°C. From the plots of logarithm of dissolution rate versus inverse of absolute temperature, the values of activation energy and pre-exponential factor for the dissolution process are computed. It is found that for H₃PO₄ concentrations upto 22.05 N the value of the activation energy remains constant but that of pre-exponential factor increases with acid concentration. At higher concentrations, the activation energy decreases. The results are systematically described and discussed.     

Atomic Force Microscopy Studies on Growth Mechanisms and Defect Formations on {110} Faces of Cadmium Mercury Thiocyanate Crystals

Growth mechanisms and defect formations on {110} faces of cadmium mercury thiocyanate crystals grown at 30°C (σ=0.24) were investigated by using atomic force microscopy (AFM). It was found that, under this condition, spiral dislocation controlled mechanism and 2D nucleation mechanism operates simultaneously and equally during growth, which is completely different from the traditional 2D nucleation and dislocation source controlled mechanisms. A number of 2D nucleus are formed at the large step terraces generated by dislocation sources, leading to the unequal growth rates of the elementary steps and thereby “step bunches” arecaused. Various defects are formed under this growth condition, which is assumed to result from the incongruence between the steps generated by different sources. A new kind of 2D defect, corresponding to one growth layer in height, was observed for the first time.     

Observation of concentration boundary layers around growing or dissolving KH2PO4 crystals in stagnant solutions

The solute concentration profiles around KH₂PO₄ crystals growing or dissoloving in stagnant aqueous solutions were studied by the schlieren method after Toepler. By this technique the thicknesses of concentration boundary layers around the crystals, formed by free convection of solution, were measured in dependence of crystal size and super (under) saturation. In the case of dissolution, theoretical estimation of the boundary layer thickness yielded a fair agreement with the observed value. For growth, the process is dominantly limited by surface kinetics, whereas volume diffusion plays a minor role.     

Crystal structures of bis{4-bromo-2-[(2-hydroxyethylimino)methyl]phenolato}copper and bis{4-chloro-2-[(2-hydroxyethylimino)methyl]phenolato}copper

The crystal structures of bis{4-bromo-2-[(2-hydroxyethylimino)methyl]phenolato}copper (I) and bis{4-chloro-2-[(2-hydroxyethylimino)methyl]phenolato}copper (II) are determined. Crystals I are monoclinic, space group P2₁/c, Z = 2, and R = 0.0732 (for all reflections). Crystals II are likewise monoclinic, space group P2₁/n, Z = 2, and R = 0.1106. In the structures of compounds I and II, the metal atom is situated at the center of symmetry and coordinated by two singly deprotonated bidentate 4-bromo-or 4-chloro-2-[(2-hydroxyethylimino)methylphenol molecules, respectively, through phenol oxygen and azomethine nitrogen atoms, which form a distorted planar square. In the structures of compound II, the coordination polyhedron of the central atom is completed to an elongated tetragonal bipyramid by the amino alcohol oxygen atoms of the adjacent complexes.     

Crystal structure of [WI2(CO)3{P(OMe)3}2]

[WI₂(CO)₃{P(OMe)₃}₂]crystallizes in the orthorhombic space group Pca2₁, with a = 26.924(5), b = 10.726(2), c = 14.136(3) Å, and Z = 8. There are two molecules in the asymmetric unit, the metal atoms in each case being seven-coordinate with a capped fac-(CO)₃ octahedral geometry. The molecular dimensions in the two molecules are nearly identical. The W–P distance to the capping atom 2.397 Å (average) is significantly shorter than the other W–P distance, 2.525 Å (average).     

Study of the Nature and Distribution of Elementary Steps on the (100) Cleavage Faces of MgO Single Crystals by Atomic Force Microscopy

Some observations made on the nature and distribution of monolayer (elementary) steps on the (100) cleavage faces of MgO single crystals by atomic force microscopy are presented and discussed. The following types of patterns of monolayer steps are described: (1) trains of steps, (2) steps terminating on the cleaved surface at the emergence points of screw dislocations, and (3) localized pinning of advancing steps at random sites (probably at the emergence points of edge dislocations). It is shown that: (1) the origins of emergence points of monolayer steps are devoid of hollow cores due to a small Burgers vector of dislocations and (2) the minimum distance between two emerging steps due to screw dislocations and between two pinning centres due to edge dislocations depends on their sign, and is determined by the mutual interaction between neighbouring dislocations.     

In situ AFM investigation of 2D nucleation on the (100) face of KDP

Surface morphology of the (100) face of potassium dihydrogen phosphate (KDP) crystals which were grown at different supersaturations at 25 °C was investigated by in situ atomic force microscopy (AFM). Various AFM images of 2D nucleation under different growth conditions were presented. It is found that the growth of KDP is controlled by polynuclear nucleation mechanism at the high supersaturation. With reduction of the supersaturation, the growth velocity of 2D nuclei becomes very slow and shows typical anisotropy. It is found that the process of coalescence of 2D nuclei does not lead to defect. The experiments show that the growth mechanism for KDP at 25 °C changes between step flow and 2D nucleation in the supersaturation range of 4.5‐5%. The triangular nuclei which are close to equilateral triangle are observed in the experiment at the supersaturation σ = 6% for the first time, showing typical anisotropic growth. Through observing the dissolution of 2D nuclei, the dissolving process can be regarded as the reverse process of growth. We also find that the microcrystals landing on the surface at σ = 9% would grow and coalesce with each other and there is no observable defect in the coalescence. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

不同pH值下ZTS晶体(100)面台阶生长动力学规律和位错缺陷的研究

通过利用光学显微镜,对不同pH值下ZTS晶体(100)面的台阶推移过程进行了实时观察,发现在同一过饱和度下,调高生长溶液的pH值会导致台阶推移速率降低;而调低pH值时,台阶的平均推移速率增大,当pH =4.2时,(100)面生长速度最快.计算出不同pH值下的台阶动力学系数βl和台阶活化能E的数值.对不同pH值下生长出的ZTS晶体的(100)面进行了位错缺陷观察,发现pH =4.2时,位错密度较低,有利于晶体生长质量的提高.     

Investigations of LiInSe2 Epitaxial Layers on {100}- and {110}-oriented Substrates with Sphalerite Structure by Means of RHEED

Epitaxial LiInSe₂ films were deposited by flash evaporation technique on {100}, {110} GaAs and {100} GaP. By means of geometrical considerations based on the concept of corresponding substrate and deposit planes epitaxial relationships can be predicted and compared with results from reflection high energy electron diffraction (RHEED). The epitaxial relationships are given for both rhombic (β-NaFeO₂-type) and tetragonal (chalcopyrite-type) LiInSe₂ deposits on {100}- and {110}-oriented sphalerite-type substrates.     

Crystal structures of two modifications of sodium pentahydrogendiphosphate NaH5(PO4)2

Two crystalline modifications of NaH₅(PO₄)₂ are obtained by the reaction of Na₂CO₃ with an excess of orthophosphoric acid. The crystal structures of α-and β-NaH₅(PO₄)₂ are determined by X-ray diffraction analysis. The crystal data are a = 8.484(4) Å, b = 7.842(3) Å, c = 10.353(4) Å, β = 90.50(3)°, V = 689.3(3) ų, space group P2₁/c, Z = 4, and R ₁ = 0.0250 for the α modification and a = 7.127(2) Å, b = 13.346(4) Å, c = 7.177(2) Å, β = 95.5(2)°, V = 679.5(3) ų, space group P2₁/c, Z = 4, and R ₁ = 0.0232 for the β modification. Based of the hydrogen-bond system, the formulas of the α and β modifications can be represented as Na(H₂PO₄)(H₃PO₄) and Na[H(H₂PO₄)₂], respectively. They correspond to the stable and metastable forms of the compound.     

Synthesis and Crystal Structure of Dichlorido{2-[(4-Methoxyphenyl)Iminomethyl]pyridine-k2N,N'}zinc

Crystallography Reports - A coordination complex, [Zn(L)Cl2], consisting of ZnCl2 and Schiff base bidentate ligand (4-methoxyphenyl)pyridine-2ylmethyleneamine (L) was prepared and structurally...     

坩埚下降法钨酸铋钠晶体生长及其生长面研究

本文用坩埚下降法自发成核的方法生长了钨酸铋钠NaBi(WO4)2晶体,得到了尺寸达18×18 × 52 mm3的透明晶体.研究了该晶体的生长面,发现晶体的生长面以(001)面为主,并运用布拉维(Bravais)法则和负离子配位多面体生长基元理论对这一现象进行了分析.     

H3PO4 — etching of {001}-faces of InP, (GaIn)P,GaP, and Ga(AsP)

This paper shows that hot H₃PO₄ is a suitable etchant for the production of dislocation etch pits on {001}-InP, (InGa)P, GaP, Ga(AsP), and {111}-GaP. The effects upon etch pit morphology of the misorientation of samples and the type of dislocations are investigated in detail.     

Ca(H2PO4)2-H3PO4-K2SO4体系中石膏晶型及形貌调控

为将Ca(H₂PO₄)₂制备KH₂PO₄过程中的石膏资源化利用,以H₃PO₄与CaCO₃反应制备Ca(H₂PO₄)₂溶液,并与K₂SO₄溶液反应,进行Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄体系中石膏晶型和形貌调控研究。结果表明:通过改变反应时间、反应温度、SO^2-₄过量系数和CaO含量等参数可对Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄体系中石膏晶型和形貌进行调控,制得短柱状α-CaSO₄·0.5H₂O。体系在温度高于95 ℃和CaO含量为3.0%~5.0%(质量分数,下同)时形成α-CaSO₄·0.5H₂O,在CaO含量为5.5%主要形成CaSO₄·2H₂O;反应时间长于20 min和SO^2-₄过量系数大于1.4将形成K₂SO₄(CaSO₄)₅·H₂O,导致石膏晶体表面缺陷增加。本实验条件下,适宜反应条件为:反应时间10 min、反应温度95 ℃、SO^2-₄过量系数1.2和CaO含量5.0%,此条件下可制得长度42~70 μm、直径13~24 μm的短柱状α-CaSO₄·0.5H₂O,其抗折和抗压强度分别可达5.61 MPa和33.74 MPa,滤液中钾收率和脱钙率分别可达94.23%和83.80%。     

Kinetics of Mixed Crystal K2(SO4, CrO4) Growth from Aqueous Solution

The investigation of crystal growth kinetics and phase equilibria in the system K₂SO₄–K₂CrO₄–H₂O was carried out using the method for the determination of the saturation temperature and the growth rate by microscopic observation of the seed crystal behaviour. The kinetics of mixed crystal growth can be characterized by the expression V = 450.24σ^1,6,2, where σ is the value of effective supersaturation of the solution calculated by taking into account the specific features of the phase equilibria diagram. Use of this criterion allows the control of the rate of delta crystal growth from solutions of variable composition.     

Effect of pH value on the growth morphology of KH2PO4 crystal grown in defined crystallographic direction

KH₂PO₄ single crystals were grown in aqueous solution at different pH values by using “point seeds” with a defined crystallographic direction at 59 degree to the Z axis. Atomic Force Microscope (AFM) was applied to observe the surface morphology of (100) face. It was found that at the same supersaturation, the larger steps appeared at the lower pH value before appearance of 2D nucleus. We found that 2D nucleus was occurred at σ ≤ 0.04 when pH value is <2.8. The occurrence of 2D nucleus was caused by the decreasing step‐edge free energy with the decreasing of pH value in the growth solution. In this paper, we observed the morphologies of (100) faces of KDP crystals which grew in solutions with different pH values. 2D nucleuses appeared on the terrace of growth steps when pH value down to 2.8 and 3.2 at supersaturation of 0.04, while pH value down to 2.4, only 2D nucleation control the growth. Therefore, the pH value can change the growth mechanism of KDP crystals.     

反式二苯乙烯(TSB)晶体的溶液法生长研究进展

反式二苯乙烯(TSB)晶体是一种可用于较强γ辐射下进行快中子检测的优良闪烁材料.由于溶液法得到的晶体在质量、性能等方面所表现的优越性,有必要对TSB晶体的溶液法生长技术进行系统研究.本文介绍了国内外关于TSB晶体的溶液降温法生长研究过程和取得的进展,对相应研究结果进行了分析,并提出了尚存在的问题.     

Crystal Growth and Elastic Properties of Hopeite,Zn3(PO4) · 4 H2O

Single crystals of orthorhombic Zn₃(PO₄)₃ · 4 H₂O of optical quality with dimensions up to 12 × 10 × 8 mm were grown from aqueous solutions of ZnSO₄ and NaH₂PO₄ by controlled diffusion of NH₃ into the solution. The elastic constants c_ij and the thermoelastic constants T_ij = dc_ij/dT, T temperature, were determined from ultrasonic resonance frequencies of thick plates in the range between 5 and 40 MHz and between 250 and 320 K. In respect to the longitudinal elastic stiffness hopeite behaves quasi isotropically, however, the elastic shear stiffness shows a large anisotropy of about a factor 2.5. Above 260 K the shear stiffness c₆₆ possesses a quite anomalous temperature dependence (T₆₆ > 0). Further, the linear thermal expansion reveals a strong anisotropy (α₁₁ = −3.3, α₂₂ = 3.4, α₃₃ = 33 · 10⁻⁶/K).