On the incorporation mechanism and distribution mode of impurities in potassium acid phthalate crystals grown from aqueous solutions

Mechanism of impurity structure formation in crystals grown from aqueous solutions has been studied on the example of potassium acid phtalate (abbreviated hereafter as KAP) single crystals. Gold decoration technique at an electronmicroscopic scale has been applied to the study of the distribution of uncontrolled impurities on KAP cleavage face (010) after 10, 20 and 30 days of growth, taking into consideration different growth rates in 〈001〉 and 〈001 〈 directions. A technique for visualization of impurities in water, based on the adsorption of these impurities by the surface of amorphous film of nitrocellulose (parlodion) and the vacuum decoration with gold of these impurities, has been developed. Differences in the impurity structure of KAP regions located in 〈001〉 and 〈001〉 directions from the seed have been established. In 〈001〉 direction after 20 days of growth impurity assemblies 0.1—0.4 μm in size are revealed, and in 〈001〉 direction heterogeneous impurity structure is revealed only after 30 days of growth. The real (impurity) structure of KAP outside impurity assemblies is quite homogeneous and is the same throughout the whole crystal volume, the impurities incorporating mainly into complex active centres. From comparison of the changes in time of the impurity structure of water used for crystallization solutions and the impurity structure of KAP crystals a conclusion is made that the impurity structure of crystals is “programmed” in the impurity structure of crystallization solutions which regularly changes with time, i. e. impurities from different kinds of assemblies which are selectively adsorbed by the growing crystal faces. The role of the adjacent to the growing face interfacial layers which control the growth rate and have a complex impurity structure is stressed.     

On the mechanism of trace-element uptake during the hydrothermal growth of sulfide mineral crystals

The stable species of cadmium and mercury are formed in iron and lead sulfides at elevated temperatures and pressures under hydrothermal conditions. Their formation proceeds through different mechanisms. The most general mechanism involves the uptake of trace elements in the form of structural species due to isomorphous exchange. The results obtained for cadmium in pyrrhotite indicate that structural defects substantially affect the incorporation of impurities into the crystal structure. It is found that trace elements are accumulated on the surface in the absence of defects and are incorporated into the crystal bulk in the form of structural impurities in the presence of defects. Moreover, at elevated temperatures and pressures, trace elements can form their own (surface nonautonomous) phases. These phases are formed not only at trace-element concentrations close to saturation (Cd in Fe_1.0S) but also under conditions far from saturation as a result of the interaction of trace elements with the oxidized surface of the mineral (the cadmium uptake by galena with the formation of either a sulfate surface phase or a sulfate-chloride surface phase). An important mechanism of trace-element uptake by sulfides during the hydrothermal growth of crystals is associated with external and internal adsorption of impurities by defects. This adsorption manifests itself both in an increase in the content of sorbed mercury in galena at a high sulfur activity due to the interaction of mercury with lead vacancies and in the formation of dislocation cadmium species, which results in an increase in the coefficient of cadmium distribution in the crystal-solution system.     

The influence of melt stirring intensity on the axial impurity distribution in proustite single crystals grown by the Stockbarger method using ACRT

The influence of modulated crucible rotation on the axial distribution of Cu, Mg and Si impurities in proustite single crystals grown by the Stockbarger method using ACRT is studied in a wide range of Taylor numbers (1.9·10⁵ < Ta < 7.12·10⁷). The impurity content in the upper part and in the tail portion of the grown crystals is measured using X‐ray‐phase analysis. Micro and macrostriations are observed in the grown crystals. The wavelengths of impurity content fluctuations have been determined. The microfluctuations of axial impurity content are caused by modulated crucible rotation. The studies have revealed that the ACRT provides an effective removal of impurities from the main part of the grown crystal at high intensity of melt stirring, and consequently, the ACRT can be applied validly to decrease the impurity content during the growing of high‐quality proustite single crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal analcime synthesis at 10 MPa isobar

Hydrothermal analcime synthesis at 10 MPa isobar and 100, 200, and 300 °C isotherms was performed. As synthesis initial components the minerals nepheline, albite, natrolite, jadeite, wairakite and the mixtures nepheline + albite and nepheline + natrolite were used. 1 M Na₂SiO₃, 1 M NaCl and 0.1 M NaOH (pH = 14, 7, 13) solutions were applied as the hydrothermal medium. On evaluating the synthesis products by means of X-ray diffraction analysis and X-ray microanalysis (EDAX) it was estimated that different analcime structural modifications originate especially at temperatures above 200 °C in neutral and alkaline medium from all the mentioned minerals. Analcime with a higher symmetry of the unit cell of crystals form at temperatures above 250 °C particularly.     

Colour Centre in Nd3+-doped Yttrium Aluminates

Spectroscopic and laser properties of YAG:Nd and YAP:Nd grown from the nonstoichiometric melts or those containing Mo and Fe impurity were compared. YAG:Nd grown from the melt with surplus of Y₂O₃ and annealed in H₂ at ∼ 1400 °C have an increased laser performance. Mo admixture in hydrogen annealed YAP:Nd laser crystals suppresses effectively the detrimental action of iron impurity.     

Epitaxial growth of very pure NiO single crystals

This paper describes the procedure for growing epitaxial single crystals of NiO with a minimum content of impurities. Particular attention is paid to details of the starting material as well as to the cleaning and handling of the apparatus. Crystals with a total cation impurity content of less than 20 ppm are now grown routinely.     

Effect of impurities on the optical properties of PbWO<Subscript>4</Subscript> crystals

The effect of excess W and La³⁺, Y³⁺, and Mo⁶⁺ impurities on the luminescence spectra and the thermally stimulated luminescence of PbWO₄ crystals is studied. A high tungsten content (up to 1 at %) in the charge mixture results in a high luminescence intensity in the green spectral region. Lanthanum impurity decreases the transmission in the short-wavelength (k > 29 000 cm^?1) spectral region. Lanthanum and yttrium impurities decrease the luminescence intensity. At low (10² ppm) concentrations, Mo impurity can somewhat increase the light yield. However, the presence of Mo in PbWO₄ shifts the absorption-band edge to longer wavelengths, while an increase in the Mo concentration above 10² ppm decreases the luminescence intensity.     

Influence of impurities,irradiation and temperature on the mechanical and electrical properties of LiF crystals

On the basis of study of the temperature dependence of mechanical and electrical properties of LiF crystals with different impurities an evident interaction between radiation defects and impurities is revealed. As a result of trapping of radiation defects (F- and H-aggregate colour centres) by impurity centres the reconstruction of impurity centres takes place, causing a change of mechanical and electrical properties.     

Growth and basic dielectric data of high quality TSCC crystals

Tris-sarcosine calcium chloride (TSCC) single crystals were grown from water solutions by the isothermal evaporation method. The growth solutions contained sarcosine and CaCl₂ either in stoichiometric or nonstoichiometric ratio. The required phase diagram sarcosine–CaCl₂ H₂O at 40 °C was determined by the synthetic method. PFT 400 MHz NMR was used for the analysis of organic impurities in sarcosine and TSCC. The crystals grown from both types of solutions had maximum values of the dielectric permittivity 10 to 200 times larger than those measured by other authors at comparable measuring frequencies and fields. It is discussed in terms of crystal quality.     

The Influence of Impurities on Crystallization Kinetics of Sodium Chloride

The influence of impurities on the crystallization kinetics of NaCl was investigated in a fluidized bed crystallizer. The growth and dissolution rates were related to the supersaturation and impurity concentrations. The effect of different impurities on the growth rate of NaCl crystals can be divided into thermodynamic effects where the impurities influence the solubility and kinetic effects where the impurities will suppress the growth rate compared to the pure NaCl. A mathematical model describing crystal growth rates from aqueous solution as a function of impurity concentration is presented. The model explains impurity concentration effects on the crystal growth rate in terms of an impurity effectiveness factor and a Langmuir adsorption isotherm for the impurity.     

Investigations on Flux Grown Cadmium Sulphide Crystals

Observations on surface microtopography of flux grown CdS crystals are reported. Crystals resulting with cooling rate above 30 °C/hr are reported to be dendritic crystals, while those with cooling rate below 30 °C/hr are reported to be normal crystals like mineral greenockite as reported in standard books on mineralogy. Reasoning for dendritic growth is briefly discussed. Growth patterns and etch pits formation on them are interpreted. It is established that these crystals grow by two-dimensional nucleation mechanism and by spreading and piling of growth layers.     

氧化锌单晶的水热生长与结晶习性

本文应用水热生长法,采用双温区高压反应釜,黄金内衬(φ35mm ×2mm),碱性溶液矿化剂,生长出了毫米级的透明氧化锌单晶,最大单晶可达2mm ×3mm ×6mm.所生长氧化锌晶体为纤锌矿型的六方晶体,晶体呈上部锥形的六棱柱体,{10(1-)1}、{10(1-)0}和{000(1-)}面有较大的显露平面.本文中从温差和填充度方面研究了实验条件对ZnO晶体的生长及其形貌的影响,使用黄金内衬前后的结果表明,用贵金属内衬可以有效阻止釜内壁杂质的进入,使晶体完整透明.     

Phosphoric acid purification by suspension melt crystallization: Parametric study of the crystallization and sweating steps

In order to purify phosphoric acid, the suspension melt crystallization process was studied. The suspension crystallization experiments were carried out with 80, 84 and 88 wt% phosphoric acid melt at the cooling rates of 0.05, 0.1 and 0.2 K/min, respectively. Sweating experiments were executed for various crystals obtained in suspension crystallization step. The purification effects of the sweating parameters including sweating time, initial inclusion amount and initial impurity content were studied. The inclusion fraction increases with the increase in cooling rate. The inclusion fraction of the crystals which were formed with feed concentration of 84 wt% phosphoric acid melt is lowest among the three feed concentrations. Different impurities have different purification performances during sweating. High inclusion amount and low impurity concentration favor the purification of H₃PO₄·0.5H₂O crystals during sweating.     

Electron probe microanalysis of CuInSe2 and CuGaSe2 crystals

A correction procedure for the quantitative electron probe microanalysis of nonstoichiometric crystals in the system CuInSe₂–CuGaSe₂ is presented and applied to the analysis of the terminal members of the mixtures. In CuInSe₂ samples a precipitation of Cu₂Se takes place due to an evaporation of volatile compounds with a composition ratio In: Se = 2:3. A similar reaction was observed in the case of CuGaSe₂.     

Synthesis of anisotropic gold nanoparticles using xylitol as a dual functional reductant and stabilizer

The morphology of gold nanoparticles was controlled with hydrogentetrachloroaurate (HAuCl₄) and xylitol through a hydrothermal process using xylitol as reducing agent and controlled reagent. The molar ratio of xylitol relative to HAuCl₄, reaction time and temperature played important roles in determining the geometric shape and size of the product. These nanoplates were single crystals with planar width of 80‐500 nm. The formation of nanobelts and two‐dimensional single‐crystal nanosheets is explained by the preferential adsorption of xylitol molecules from the solution onto the {111} planes of Au nuclei. These nanosheets could be used, for example, in gas sensors, in the fabrication of nanodevices and substrate materials, in property studies, and also for inducing hypothermia in tumors. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of impurity atmosphere on the deformation of silicon crystals

The Alexander–Haasen theory, which describes the deformation kinetics of silicon crystals, has been generalized for impurity crystals. The deformation kinetics of an impurity sample is calculated in a wide range of parameters, including the cases of partial and complete entrainment of impurities by moving dislocations. The developed model, despite its simplicity, adequately describes the qualitative transformation of the stress–strain curves of impurity silicon crystals in dependence of the impurity concentration and other material parameters. The manifestation of negative velocity dependence of the yield stress, observed in natural experiments, is analyzed.     

Growth kinetics of ammonium oxalate monohydrate single crystals from aqueous solutions containing Co(II) and Ni(II) impurities

The growth kinetics of different faces of ammonium oxalate monohydrate (AO) single crystals from aqueous solutions containing different concentrations of Co(II) and Ni(II) ions at a constant temperature are described and discussed. It was found that: (1) at a given supersaturation σ, both Co(II) and Ni(II) ions lead to a decrease in the growth rates R of different faces of AO crystals, (2) the growth of a particular face of the crystals occurs above a critical supersaturation σ_d, but there is also another supersaturation barrier σ* when the rate abruptly increases with σ, and (3) the values of σ_d and σ* increase with increasing concentration c_i of the impurity. The experimental R(σ) data for different concentrations c_i of the impurities were analysed according to the model involving complex source of cooperating screw dislocations and concepts of instantaneous and time‐dependent impurity adsorption. Analysis of the data showed that: (1) adsorption of Co(II) and Ni(II) impurities occurs on the surface terrace of AO crystals, (2) there is a simple relationship between Langmuir constant K and the impurity concentration c_i* corresponding to maximum surface coverage, and (3) the ratio σ_d/σ* of the supersaturation barriers observed in the presence of both impurities increases with an increase in impurity concentration c_i, and may be explained from the standpoint of the mechanism of adsorption of impurity particles at kinks and ledges. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Memory effect in CuAsSe glasses containing small amounts of Au

The Cu, As and Se contents of Au-containing CuAsSe glasses significantly affected both the resistivity in the memory state and the time required to reach the memory state, whereas the Au content affects only the latter. The main crystalline species formed in these glasses was a CuAsSe compound, and its formation was enhanced by the addition of Au. The role of Au in the memory effect was discussed on the basis of crystallization behavior of glasses.     

A detailed study of gold single crystal growth in a silica gel

Gold single microcrystals have been fabricated by electrochemical growth in a silica gel. Structural characterization of the single crystals by backscatter electron diffraction showed a preferred orientation of Au (1 1 1) and a minor orientation of Au (1 0 0). In addition, the influence of additives on the nucleation and growth of gold microcrystals has been studied. It was found that the inclusion of chemical additives in the growth solutions altered the characteristics of the gold crystals. Possible mechanisms for nucleation and growth of these crystals are discussed.     

The defect structure of CdS crystals heavy doped with Cu,Se. and Zn atoms

In this paper the defect structure of CdS crystals doped with Cu, Se and Zn atoms has been investigated. There were used two X-ray methods: the oscillating slit and oscillating film methods. CdS crystals were obtained from the melt under pressure of Se and Zn 0.5, 0.75, 1% wt and Cu 0.25, 0.5, 0.75, 1% wt in relation to CdS crystals. It was proved that high doping damages the structure of CdS crystals and that especially Cu impurity much more disturbs the crystal lattice than Zn one. Se atoms cause rather small deformation of crystal and increase the lattice constant, this being connected with decreasing of energy gap.