Study on the Growth of Triglycinsulphate Single Crystals

Crystallization of TGS at 52.0°C - above the transition point - has been studied in a wide range of supersaturation of the solution (σ = 0 to 10⁻²). The rates of growth of {110} and {001} faces were measured as a function of supersaturation at constant hydrodynamical conditions (Re = 3.4 · 10⁻³). Further, the influence of hydrodynamical conditions on the growth of {110} faces at constant supersaturation (σ = 4.2 · 10⁻³) was established. The parameters of the experimentally found dependences are determined on the basis of the surface-diffusion model of BURTON . CABRERA and FRANK . From these dependences follows that the growth rate of the {110} faces is already almost limited by the volume diffusion of TGS molecules towards the crystal surface, while in the case of {001} faces the surface diffusion mechanism of crystallization is clearly manifested. Dislocation densities in the crystals have been determined by means of etching technique. The number of dislocations increases with increasing supersaturation; hence, supersaturation of the solution together with the processes taking place in the regeneration zone surrounding the seed determine the number of dislocations in the crystal volume and thus the resulting structural perfection of single crystals. Investigation of the spontaneous redistribution of domains showed that the growth rate of TGS crystals influences the dielectric properties to much smaller extent than does chemical purity.     

Ferrous Tartrate recognition of sodium chloride {111} and its effect on crystal growth

The surface morphology and growth pattern of some molecules could be altered by the recognition of ferrous tartrate (FeC₄H₄O₆, FeTA). We have explored this phenomenon in the aspect of growth rate and morphology alteration of sodium chloride crystals where few researches have been done. In this paper, the crystallization behavior of NaCl with added FeTA was studied by supersaturation test, conductivity, scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The results showed that the supersaturation of NaCl solution could be increased to about 5.5 % in presence of FeTA prior to the onset of crystallization. Furthermore, SEM images and XRD results indicated that the addition of FeTA could change the morphology of NaCl crystal from cubic to octahedron by impeding the growth of {111} and {110} faces. Besides, the interaction between NaCl {111} face and FeTA was discussed and the possible spatial structure of FeTA was speculated through the lattice parameters of NaCl.     

Understanding supersaturation‐dependent crystal growth of L‐alanine in aqueous solution

The dependence of crystal growth rate of L‐alanine on solution supersaturation was investigated by combining experiments and molecular dynamics (MD) simulations. The experimental results show that lower supersaturated solution yields more elongated L‐alanine crystals along the c‐axis, i.e., the aspect ratio (c/b) of the crystal decreases with the increase of solution supersaturation, which is due to the higher supersaturation inducing a rise in the relative growth rate between the main side surface (the (120) surface) and the main end surface (the (011) surface). MD simulations on the two surfaces in contact with different supersaturated solutions revealed that the solute molecules tend to be more efficiently attached to the (011) surface than to the (120) surface at both supersaturations studied, as the interaction between the solute molecules and the L‐alanine molecules in the first layer of the (011) surface is stronger than that of the (120) surface. However, higher supersaturation leads to larger relative interaction energy between the (120) and (011) surfaces, suggesting an increase in the relative growth rate of the two surfaces (R₍₁₂₀₎/R₍₀₁₁₎) with supersaturation, which is in agreement with the experimental results.     

Twins in CdMnTe single crystals grown by Bridgman method

Cd_1‐xMn_xTe (x =0.2, CdMnTe) crystal was grown by the vertical Bridgman method, which exhibits a pure zincblende structure in the whole ingot. The major defect, twins, which is fatal to CdMnTe crystal, was analyzed with scanning electron microscopy (SEM), X‐ray energy disperse spectroscopy (XEDS) and optic microscopy on the chemical etching surface. The twins observed in the as‐grown ingot are mainly lamellar ones, which lie on the {111} faces from the first‐to‐freeze region of the ingot and run parallel to the growth axis of the ingot. Coherent twins with {115}_t‐{111}_h orientations when indexed with respect to both the twin and host orientations, are often found to be terminated by {110}_t‐{114}_h lateral twins. Te inclusions with about 20 μm in width are observed to preferentially decorate the lamellar twin boundaries. The origin of the twins, relating to the growth twin and the phase transformation twin, is also discussed in this paper. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In situ measurement of growth kinetics of {100} KDP crystal faces in the presence of polyphosphate impurities

The face growth rate and critical supersaturation of {100} face were in situ measured using the laser‐polarization‐interference technique in the presence of potassium pyrophosphate, trimetric sodium phosphate and sodium hexametaphosphate impurities. The polyphosphate impurities inhibit the growth rate of prismatic faces. The face growth rate as a function of supersaturation at different impurity concentrations, as well as critical supersaturation as a function of impurity concentrations, was found in good agreement with a two‐dimensional nucleation model in the pure system and Kubota and Mullin's model in the presence of impurities. The average distance L between active sites available for impurity adsorption as well as the edge free energy was calculated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vapor phase epitaxy of CdTe on sapphire substrates in dependence on the vapor-flow orientation

The growth of cadmium telluride films on a structured (0001) sapphire surface oriented at an angle of 44° to the vapor-flow direction and normal to the steps formed along the \(11\overline 2 0\) direction is studied. It is found that this geometry of the vapor source and a substrate (heated to a temperature of 300°С) provides the growth of single-crystal CdTe films if a step height on the substrate surface is more than 1 nm. The results are explained by the occurrence of a longitudinal component of the diffusion flux of СdTe molecules and atoms toward the steps from the inner side and their high density at the step edge from the outer side due to the presence of the Ehrlich–Schwoebel barrier, which ensures the efficient supply of material and minimum supersaturation necessary for the nucleation at the step edge and growth of oriented CdTe islands. The cadmium telluride films that are grown have the \(\left( {110} \right)\left[ {1\overline 1 0} \right]CdTe\left\| {\left( {0001} \right)} \right.\left[ {11\overline 2 0} \right]A{l_2}{O_3}\) orientation and a composition similar to stoichiometric CdTe.     

Facet Formation in Garnet Crystals

Formation of {110} and {211} type facets in rare-earth aluminium garnet crystals grown along different crystallographic directions is analyzed and it is shown that D/2R parameter (where D is the crystal diameter and R is the curvature radius of spherical growth interface) may be used to characterize the number of originating facets and their configuration in crystals.     

The Morphology of Hydrothermally Grown Plagioclase

Plagioclase crystals Ab₂₀An₀₀ and nearly pure anorthite were grown on the surface of artificial melts by hydrothermal treatment at 2 kb. The average crystal size was 0.002 to 0.008 mm. In the temperature range of 400° to 600°C a pseudohexagonal habit was observed for anorthite while a lath-like habit due to the prevalence of {010} was found for the Ab₂₀An₈₀ composition. Dominating faces are {010} {130} {110} {100} {110} {130} in the zone [001] and {021} {111} {111} {021} {111} {111} together with {001}.     

Direct Growth of Aggregates on {110} Faces of Cadmium Mercury Thiocyanate Crystals

New growth phenomena ‐ direct incorporation of aggregates have been observed on the {110} faces of cadmium mercury thiocyanate CdHg(SCN)₄ crystals by atomic force microscopy. These aggregates grow in two forms: some directly cover up the steps and forms new growth layers; while others are just incorporated at the step edges. These aggregates, which are mostly oriented along [111] direction, are formed by small columnar structural units. The aggregates have the similar structure of CdHg(SCN)₄ crystals and greatly vary in nature with the variation of solution supersaturation σ and growth time t. With the increase of σ the aggregates become larger, consistent with the variation of growth units dimension with the supersaturation; and with the increase of growth time the aggregates become more structurally substantial. These observations have led to a new understanding about the crystal growth.     

Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: I. Growth habit and surface morphology

The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as‐grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30 °C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH₄)₂C₂O₄ · H₂O molecules are in excellent agreement with the low‐index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph.     

Study of growth kinetics of ammonium oxalate monohydrate crystals from aqueous solutions

Experimental results of the dependence of linear growth rates of ammonium oxalate monohydrate [(NH₄)₂C₂O₄ · H₂O; AO] single crystals on solution supersaturation are presented. The AO crystals were grown by constant-temperature, constant-supersaturation method at 30 and 40 °C in the supersaturation range of 1–9%. It was observed that the supersaturation dependence of growth rates follows the parabolic growth law. Analysis of the supersaturation dependence of linear growth rates of AO crystals showed (1) that growth models involving surface diffusion and direct incorporation of growth units give kinetic parameters similar to those reported for other compounds grown from solutions, and (2) that the the BCF model of cooperating screw dislocations is also applicable. An inverse relationship between the estimated values of the length, L, of the line containing the dislocations and growth rate, R, and a direct relationship between L and interplanar distance, d_hkl, of the face {hkl} were found. Both these relationships are associated with the process of generation of screw dislocations in the growing layer.     

Die realstruktur von aus der gasphase gewachsenen molybdän- und wolfram- einkristallen

The morphology and crystal perfection of single crystals of molybdenum and tungsten obtained by vapour deposition using the thermal decomposition of halides, depends on the supersaturation. The crystals were examined by metallographic investigations and X-rays in order to determine position, extension and kind of the disturbances. These investigations show that at lower supersaturations with {110} as the equilibrium form face, disturbances appear regularly in layers and within defined crystallographic positions, which depend on the growth direction in different {110} planes. In most cases it was found that the disturbed layer appears in the mirror plane of the planes containing the growth steps.     

Darstellung,Struktur und Eigenschaften von Nb-, Mo-, W- und Ru-dotiertem VO2

Monocrystals of doped VO₂ having the general composition V_1–xMe_xO₂ were prepared by chemical transport with TeCl₄. A summary of the morphological, structural, electric and magnetic properties is given. The habit of the doped crystals depends on the doping factor x. The boundary surfaces are {110}-prismatic and {111} pyramidal ones. At x = 0.04 the lattice constants change rapidly between the monoclinic M1-and the tetragonal R-phase. The typical change of resistance, which amounts four orders of magnitude for pure VO₂, and the transition temperature T_c decrease with increasing x.     

In situ Observed Twin Formation on ZnSe Crystals Growing by Sublimation

ZnSe crystals were grown by sublimation in closed ampoules between 1335 K and 1365 K. The growth was observed in situ with a video camera after an abrupt change of the supersaturation. The crystals developed preferably {110} faces. Repeatedly a nucleus was formed in ortho-twin position on a small {111} face which truncated the corner of three adjacent {110} faces. The repeated twin formation led to a preferred growth into the relevant 〈111〉 direction. The twinning already occurred at a low supercooling of less than 1 K and accelerated the growth distinctly.     

Die Molekül- und Kristallstruktur des Morpholyl-pentamethin-merocyanins C9O2NH13

The morpholyl-pentamethine-merocyanine crystallizes within the space group \documentclass{article}\pagestyle{empty}\begin{document}$ P\frac{{{\rm 2}_{\rm 1} }}{{\rm a}} $\end{document} with the lattice constants being a = 13.269 Å, b = 15.232 Å, c = 4.513 Å, β = 94.05°. The bond lengths between the methine-carbon atoms within the pentamethine chain alternate significantly, and thus show a distinct polyenal course. Simultaneously, short C–N (1.339 Å) and short C–O bond lengths (1.224 Å) of the substituents N and O towards the pentamethine chain occur. As with open chained cyanines we also find with this merocyanine a distinct alternation of the valence angles at the methine-carbon atoms. Distances of substituents and alternation of valence angles point to a poylmethinic behaviour of the molecules. The presented merocyanine therefore takes a mean position between a polyenal and a polymethinic behaviour, sharply to be limited by X-ray crystal structure analysis. The experimentally determined geometry of the molecule is compared with quantum mechanical calculations and different structure chemical ideas. On the base of the resonance theory new limiting structures are introduced, the consideration of which enables to give an explanation of the molecule's geometry also in the formalism of mesomerism. The geometry of the chair formed morpholyl ring as well as the packing of the molecules in the crystal bond (intermolecular interaction) are discussed in detail.     

Crystal and Molecular Structures of Modified Progestagens (IV). 17α-Azidomethyl-17β-hydroxy-estra-4,9-dien-3-one,C19H25N3O2

The crystal and molecular structure of 17α-azidomethyl-17β-hydroxy-estra-4,9-dien-3-one has been determined by X-ray structure analysis. It crystallizes in the orthorhombie space group P 2₁2₁2₁ with cell parameters a = 9.118(1), b = 9.252(1), and c = 20.444(2) Å. The structure was solved by MULTAN-82 and refined to R = 0.042 for 1408 observed reflections. Steroid ring and 17β-side chain conformations are discussed in the paper. Intermolecular hydrogen bridges between hydroxyl groups and carbonyl oxygen atoms link molecules forming chains in c-direction.     

Crystal Structure of 2-{1-[(1-(2-Pyridinio)ethylidene)hydrazono]ethyl}pyridinium diperchlorate,the Product of Template Condensation in the Presence of Cr(III)

Abstract  In an attempt to synthesize a Cr(III) complex of 2′-[1-(2-pyridinyl)ethylidene]oxamohydrazide an azine product 2-{1-[(1-(2-pyridinio)ethylidene)hydrazono]ethyl}pyridinium diperchlorate was obtained by an electrophilic acyl substitution catalyzed by Cr(III). Its structure was determined by X-ray crystal analysis and showed significant changes in comparison to the corresponding unprotonated compound. The 2-{1-[(1-(2-pyridinio)ethylidene)hydrazono]ethyl}pyridinium diperchlorate crystallizes in the space group P2₁/n of the monoclinic crystal system with unit cell parameters a = 14.3809(3) ?, b = 24.1516(5) ?, c = 15.4471(3) ?, β = 99.930(2)°, V = 5284.74(19) ?³ and Z = 12, i.e. three molecules per asymmetric unit. Graphical Abstract  In the template condensation of the 2′-[1-(2-pyridinyl)ethylidene]oxamohydrazide in presence of the chromium(III) ion the 2-{1-[(1-(2-pyridinio)ethylidene)hydrazono]ethyl}pyridinium diperchlorate was obtained and characterized by NMR spectroscopy and X-ray crystallography. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of supersaturation on the crystallization of phenylbutazone polymorphs

The article describes the effect of degree of supersaturation, σ, on the crystallization of specific polymorphs of phenylbutazone from its methanolic solution at 20 °C. At low initial supersaturation, σ ≤ 2.0, the fraction of the metastable α polymorph in the crystallized product exceeds that of the δ polymorph, while at σ ≥ 5.0, the fraction of the stable δ polymorph increases in the crystallized product. The results are explained by the effect of supersaturation on the relative rates of nucleation and crystal growth of the polymorphs. Furthermore, the mechanism of nucleation and crystal growth also change with supersaturation. Supersaturated methanolic solutions of phenylbutazone exhibit a critical temperature at which the nucleation rates of the polymorphs decrease drastically. This effect is partly explained by the decreased mobility of phenylbutazone molecules at lower temperatures. Nucleation is most rapid when the crystallization temperature is close to the transition temperature, T_t(α ⟷ δ), between the polymorphs, α and δ. The nucleation rate decreases as the temperature difference between T_t(α ⟷ δ) and the crystallization temperature increases. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zum chemischen Transport der Übergangsmetalldioxide mit Tellurhalogeniden

The thermodynamic relationship between the transition metal dioxides and their tetrahalogenides is demonstrated, and a comprehensive survey on the thermodynamic values of the compounds is given. – All dioxides of the transition metals existing to 1000°C in the solid state are transportable by TeCl₄. Only those dioxides are transported by TeBr₄ which have corresponding oxide-bromides existing in the gaseous phase. – The forms of crystallographic growth are very similar. The favoured growth direction is [001], the crystal faces are {110}- and {100}-prisms, {101}- and {111}-pyramids, respectively.     

Beiträge zum Ätzen von Galliumarsenid (I) Strukturtheoretische Diskussion der erzeugten Ätzmorphologien

{111}-, {110}- and {100}-plates of GaAs have been etched in various etching solutions followed by comparing the obtained etching structures. The fundamentals of the discussion is the existing correlation between the morphology of etch pits and crystal structure. It is shown that a qualitative interpretation of the manifold etching phenomena on the above faces in a structure characteristic for GaAs can be given by including 1. the presence of primary defects as a constitutive property of real crystals and 2. the consideration of recordable influences of the surroundings.