Growth and Characterisation of (CuInTe2)1‐x(2 ZnTe)x Solid Solution Single Crystals

The crystal structure as well as the optical properties in the band gap region of (CuInTe₂)_1‐x(2 ZnTe)_x solid solution single crystals grown by directional freezing have been studied. The lattice constants exhibit a linear dependence on crystal composition. The chalcopyrite‐sphalerite phase transition was observed between x = 0.3 and x = 0.4°. The variation of the band gap with respect to crystal composition can be described by a quadratic expression.     

Results of crystal growth of bismuth-antimony alloys (Bi100–xSbx) in a microgravity environment

Results of two experiments are presented for growth of crystals from (Bi_100–xSb_x) alloys in a microgravity environment. In the growth experiments different variants of the Bridgman technique were used. It was shown that in crystal growth from the melt in closed ampoules under microgravity conditions convection can be prevented completely. Therefore it is possible to grow crystals from melts of some components under diffusion controlled conditions of mass transfer. In microgravity a reduced interaction between the melt and the confining walls was observed even if they have large contact with each other. The investigation of surface morphology corroborated the importance of surface effects for crystal growth from the melt under microgravity conditions. Measurements of electronic properties of crystals grown in microgravity showed a good quality in comparison to earth grown crystals. Because under microgravity conditions in closed ampoules the diffusion controlled mass transfer can be realized and the interaction between the melt and confining wall is reduced, homogeneous crystals with high perfection can be grown melts of some components.     

Optimization of the Growth Technology for Crystals with Garnet Structure Based on X-Ray Diffraction Data

High efficiency of the methods of double-crystal X-ray diffractometry (DCXRD) and topography for improving the growth technology of highly homogeneous crystals has been demonstrated on the example of gadolinium gallium garnet (GGG) single crystals. The main types of structural defects observed in Czochralski-grown GGG crystals are found to be macroscopic inhomogeneity of composition distribution, caused by the facet effect manifestation; microinhomogeneous distribution of impurity and main components of the composition in striations; dislocations; and second-phase inclusions. The relationship between the type and density of newly formed defects and the technological conditions for crystal growth are considered. Optimization of the composition of crystals and their growth technology made it possible to obtain high-quality dislocation-free crystals of GGG and complex-substituted garnets on its basis for magneto-optical and microwave devices, elements of solid-state lasers, and other applications.     

Structural and electrical properties of CdS thin films evaporated onto GaAs substrates

CdS thin films on GaAs substrates are prepared by single source thermal evaporation under high vacuum conditions. Films on (111)A-oriented substrates have the wurtzite structure, whereas in the case of (1 1 1 )B-oriented substrates the sphalerite structure predominates. Depositing films on pre-annealed substrates a tetragonal phase with a composition near CdGa₂S₄ was found. The electron concentration in the CdS films is influenced by the substrate temperature, the growth rate of the films, and the substrate orientation.     

Gold distribution in pyrrhotite crystals grown under hydrothermal conditions

The distribution of gold between pyrrhotite and greenockite was studied by the method of hydrothermal thermal-gradient cocrystallization of the components at a temperature of 450°C, a pressure of 1 kbar, and different activities of sulfur in the presence of As and Se impurities. The structural component of Au impurity in these minerals was selected by studying statistical samplings of the analytical data for single crystals. Ferrous greenockite incorporates a maximum of 10 ± 2 ppm Au in solid solution. The incorporation limit of Au in stoichiometric pyrrhotite was estimated to be 25 ± 9 ppm; for nonstoichiometric pyrrhotites, it is lower. The As and Se impurities barely affect the concentration of structural gold in the minerals. It was shown that constitutional vacancies in pyrrhotite do not capture Au impurity. The observed phenomenon may be the growth effect related to the surface properties of nonstoichiometric pyrrhotite crystals grown under hydrothermal conditions. Differences in the surface structure of pyrrhotites of different composition and the products of their sorption of gold were revealed by X-ray photoelectron spectroscopy.     

Growth of functional single crystals of complex compounds on the basis of the solubility phase diagrams of ternary systems

The validity of solubility phase diagrams of ternary systems for determining the optimal (concentration and temperature) dynamic growth conditions for single crystals of congruently and incongruently dissolving solid phases is shown. It is found that the optimal composition of the mother liquor for growing solid-phase single crystals corresponds to the solution in the solid-phase solubility curve that is located at the maximum distance from the points of invariant equilibria. More than 40 ternary systems have been used and more than 60 new and known large functional single crystals of stoichiometric composition and optical quality that belong to different chemical classes have been grown on their basis under dynamic conditions.     

Surface growth mechanisms and structural faulting in the growth of large single and spherulitic titanosilicate ETS-4 crystals

Morphological, surface and crystallographic analyses of titanosilicate ETS-4 products, with diverse habits ranging from spherulitic particles composed of submicron crystallites to large single crystals, are presented. Pole figures revealed that crystal surfaces with a-, b- and c- axes corresponded to 110, 010 and 001 directions, respectively. Thus, technologically important 8-membered ring pores and titania chains in ETS-4 run along the b-axis of single crystals and terminate at the smallest crystal face. Height of the spiral growth steps observed on 1 0 0 and 0 0 1 surfaces corresponded to the interplanar spacings associated with their crystallographic orientation, and is equivalent to the thickness of building units that form the ETS-4 framework. Data suggest that the more viscous synthesis mixtures, with a large driving force for growth, increased the two- and three-dimensional nucleation, while limiting the transport of nutrients to the growth surface. These conditions increase the tendency for stacking fault formation on 1 0 0 surfaces and small angle branching, which eventually results in spherulitic growth. The growth of high quality ETS-4 single crystals (from less viscous synthesis mixtures) occurred at lower surface nucleation rates. Data suggest that these high quality, large crystals grew due to one-dimensional nucleation at spiral hillocks, and indicate that under these conditions un-faulted growth is preferred.     

Über die Züchtung von ZnS-, ZnSe- und ZnTe-Einkristallen unter Anwendung der chemischen Transportreaktion

In connection with investigations on the synthesis of ZnS, ZnSe and ZnTe single crystals by chemical transport using iodine as transport agent in sealed tubes the mechanism of mass-transport and the relationship between material-transport and growth process were studied. In this way the optimum conditions for growing single crystals were found. The dependence of the transport rate on the undercooling ΔT, on the diameter of the ampoule and on the pressure in the system is described. Relative large crystals in good quality could be propared by influencing the nucleation and the growth process by help of well defined transport rates. In all cases crystals with sphalerite structure only were obtained. The habit with the most common faces (110), (111) and (211) was found to be predominant. The dominant habit is responsive to variations in the experimental parameters. The crystal perfection have been determined by etch patterns and by X-ray topography.     

Crystallization of proteins under an external electric field

An external electric field affects the crystallization of proteins when applied under some conditions of temperature, pH, and precipitating agent composition. As suggested in the theoretical part of this paper, it produces large protein concentration gradients inside the mother liquor leading to a local supersaturation area in the crystallization solution. Such an experiment has been used for the first time on the crystallization of a protein. The effects of an external electric field on the crystallization of hen egg-white lysozyme at 293 K, pH 4.5, and two NaCl concentrations (0.6–0.7 M) have been investigated using the vapor diffusion method. The application of electric field results in a smaller number of crystals with larger size. The crystals grew at the droplet surface, near the cathode. The nucleation rate is drastically reduced and this experimental method could be used to control the number of crystals in the droplet.     

Implementation of interference in a confocal laser scanning microscope and its application for in situ observation of crystal growth processes

It is shown that interference can be implemented in the optical scheme of an Olimpus Lext-3000 laser scanning microscope. The occurring interference patterns are differently localized in space, depending on the experimental conditions. Interference from opposite crystal (volume) faces can be observed under certain conditions, which makes it possible to visualize (with a high sensitivity) defects that are invisible in polarized light and the surface relief. Misorientations and deformations in a crystal can be estimated. Our analysis allowed us to interpret the in situ observed interference pattern from growing lisozyme protein crystals and K₂Co(SO₄)₂ · 6H₂O crystals.     

The effect of impurity complexes on the shape of PbTe and Bi2Te3 crystals

The causes of strong dependences of the external shapes of lead and bismuth telluride crystals grown under conditions close to equilibrium on the deviation from stoichiometric composition have been investigated. Auger-analysis of lead telluride and its solid solutions indicates the change in the character of bonding in the subsurface layers connected with appearence of smooth faces not belonging to the equilibrium shapes of pure substances. The surface phase existance has been explained on basis of statistical thermodynamics within the framework of the Guttman model and due to the formation of „the crystalline”︁ impurity complexes in a layer medium in contact with the growing crystal surface. Particles attachment to the crystal under these conditions proceeds in two stages, which facilitates crystal growth.     

On the Morphological Changes and Twinning of ZnS (Sphalerite) Crystallites under Hydrothermal Conditions

Morphological characteristics and twinning mechanism of ZnS crystals under hydrothermal conditions have been investigated in this paper. It was shown that under hydrothermal conditions the morphology of ZnS crystallites changes along the four‐fold axis directions, and the crystals are observed in a positive or negative tetrahedron, or in a combination of positive and negative tetrahedra depending on the growth conditions. The positive tetrahedral areas on the crystallites get larger with increase of the concentrations of OH^‐ and S^2‐ in solutions, whereas the twinned crystallites of ZnS taking an elliptic shape with (111) as composition plane are easily formed in weak basic solutions. It can be found that the morphologies of ZnS crystals are in accordance with the crystallization orientations of positive or negative coordination tetrahedra ([S‐Zn₄]⁶⁺, [Zn‐S₄]^6‐) in the crystal although, in some cases, the practical morphology could be greatly affected by growth conditions, and the twinning mechansim can be suggested based on the linkage of growth units of positive and negative coordination tetrahedra, which were formed in the solution. The present investigations further indicated that the crystal chemistry approach based on the linkage/incorporation of growth units previously proposed by us can be sucessfully applied to interpret the growth mechanisms of the crystals and to control a desirable morphology.     

Growth of borax crystals by spiral mechanism

Borax crystals grown at low supersaturation values are described. A brief report about microtopographical studies of these crystals is presented. Growth spirals observed on almost all the habit faces except those in contact with the bottom of the nucleation cell are described and discussed. It is established that all these crystals have platelet form in the initial stages of crystallization and as growth proceeds they develop and grow by spiral mechanism. The conditions under which the screw dislocations play the role in the development and growth of the crystals have been worked out.     

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.     

On the Reasons Leading to an Appearance of Correlated and Anticorrelated Dependences of the Minority Carrier Lifetime on the Dislocation Density in Undoped Semi-Insulating “Stoichiometric” GaAs Crystals

It is shown that in undoped semi-insulating GaAs crystals grown under the stoichiometric conditions both correlated and anticorrelated dependences of the minority carrier lifetime τ on the dislocation density N_d could be observed. The above-pointed effect is connected with a slight excess of Ga atoms (then the correlated dependence τ vs Nd appears) or of As atoms (then the anticorrelated dependence τ vs N_d appears) which inevitably exists even in “stoichiometric” GaAs crystals (i.e. in GaAs crystals of “stoichiometric” composition).     

准同型相界组分PMNT弛豫铁电单晶的畴结构与极化特性

采用坩埚下降法生长了具有准同型相界(MPB)组分的65Pb(Mg1/3Nb2/3)O3-35PbTiO3 (PMNT65/35)弛豫铁电单晶.用偏光显微镜研究了(001)、(110)和(111)三个结晶学取向的铁电畴结构,观察到明暗交替的变化.通过对极化前后电畴形状的比较,分析了极化前后铁电畴形态的变化原因.晶片极化条件为:600 V/mm 的电场并保持10～15 min.研究了极化介质不同对极化后晶片压电性能的影响.     

Impulsbelastung von NaCl- und LiF-Einkristallen mit durch Unterwasserdrahtexplosion erzeugten Stoßwellen

The most important mechanisms of electrohydraulic comminution are briefly outlined. Based on this picture, the fractures found in NaCl-single crystals after impulsive loading using exploding wire technique are shown to be essentially due to the formation of tensile stresses in an expanding cylindrical shock-wave. An estimation of tensile strength is given for {100} faces of NaCl single crystals. LiF single crystals do not exhibit fractures under the given experimental conditions. Star-like dislocation patterns are observed at high resolved shear stress in the glide system.     

Investigation for ferroelectric domains by scanning electron microscopy

Examples for the direct observation of domain structures in ferroelectric crystals by means of scanning electron microscopy are given. The results for TGS and AFB crystals with direction of the polarization vector perpendicular to the observed surface are presented with respect to temperature changes, to domain enlargement under the influence of an external electric field and to the influence of X-ray- and γ-radiation on the domain formation.     

Preparation and investigation of (CuInSe2)x(2ZnSe)1‐x and (CuInTe2)x(2ZnTe)1‐x solid solution crystals

The (CuInSe₂)_x(2ZnSe)_1‐x and (CuInTe₂)_x(2ZnTe)_1‐x solid solution crystals prepared by Bridgman method and chemical vapor transport have been studied. The nature of the crystalline phases, the local structure homogeneity and composition of these materials have been investigated by X‐ray diffraction (XRD) and Electron Probe Microanalysis (EPMA) methods. The analysis revealed the presence of chalcopyrite‐sphalerite phase transition between 0.6 ≤ X ≤ 0.7. Lattice constants, value of σ position parameter and bond length between atoms were also calculated. It was found that the lattice parameters exhibit a linear dependence versus composition. The transmission spectra of solid solution crystals in the region of the main absorption edge were studied. It was established that the optical band gap of these materials changes non‐linearly with the X composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of inclusions and causes of their formation during growth of barium metaborate crystals

The complex study of barium metaborate crystals has been undertaken with the aim to determine the conditions of their growth with the minimum density of inclusions. It is shown that almost all the inclusions are multiphase formations of the melt type, and, in addition to the mixture of the main components of the quasieutectic composition, they can also be enriched with gas-forming impurities not removed during barium metaborate synthesis. It is shown that the amount and the composition of melt-like inclusions in crystals depends on the removal of by-products of the reactions used for barium metaborate synthesis from the system, the patterns of the convective flows in the flux, the character of its flow under the interface, the axial temperature gradient in the solution, and the temperature fluctuations at the crystallization front.