The influence of thermal screens on the temperature distribution,thermal stress,and defect structure during growth of shaped sapphire crystals

The ways in which a block structure is formed in shaped sapphire single crystals grown from melt by the Stepanov method are considered. The measured temperature distributions and results of a mathematical modeling of the heat exchange in the growth zones, as well as the calculated thermoelastic fields and measured residual stresses, are reported. The possibility of effectively controlling the thermal fields and growth of block-free crystals by choosing optimal screening is shown for single crystals in the form of tubes and basal-plane-faceted ribbons.     

Ein Beitrag zur Entstehung von Spannungen und Versetzungen beim Kristallwachstum

Semiquantitative und quantitative methods for estimation, calculation, and analysis of thermoelastic stresses in the case of crystal growth from the melt are illustrated. The specific of formation of thermoplastic stresses in crystals with different rheological equations is studied. Possibilities for estimation of dislocation density and their distribution in crystals are discussed using axial temperature gradient, calculated thermoelastic stress fields, and stage of stress relaxation.     

Effect of external forces on the dielectric and pyroelectric properties of strontium-barium niobate crystals

It is shown that high-temperature annealing of strontium-barium niobate crystals increases the mobility of domain boundaries in these crystals. This effect manifests itself in a shift of the peak of the effective permittivity of annealed samples to weaker fields. It is ascertained that the polarization of strontium-barium niobate crystals caused by annealing results in their more homogeneous single-domain state. The effect of Ce and Cr impurities on the polarization state of the surface layers in strontium-barium niobate crystals is considered.     

The Influence of Substances Reducing the Surface Energy of Naphthalene Single Crystals on Plastic Flow

The effect of surface active substances on plastic flow of naphthalene single crystals is considered. The role of normal and shear stresses is revealed. Rates of single crystals flow in different glide systems under constant stress are compared. The stress of plastic flow in single crystals can be decreased in active media by as much as 50%.     

Peculiarities of light propagation in optically active absorbing crystals of the orthorhombic system

Peculiarities of the manifestation of optical activity and absorption in crystals of the orthorhombic system of the 222 class are considered. The influence of each effect on the ellipticities of eigenwaves is analyzed. The dependences of the azimuth, ellipticity, and intensity of transmitted light in directions slightly and significantly deviating from the optical axes are considered in detail. Cases are indicated where the approximate relations obtained disregarding multiple reflections and nonorthogonality of eigenwaves in crystal hold true. The differences of the simulated conoscopic patterns of the biaxial absorbing optically active crystals from the patterns of inactive or nonabsorbing crystals are analyzed.     

The influence of magnetic effects on the mechanical properties and real structure of nonmagnetic crystals

This review for the first time systematizes the results of our investigations into the influence of magnetic effects on the mechanical properties and the real structure of nonmagnetic crystals. It is found that the preliminary magnetic treatment of alkali halide crystals leads to a decrease in their solubility and a change in the microhardness and yield stress. The magnetic field strongly affects the macroplasticity of LiF, NaCl, and PbS crystals under deformation in a magnetic field. This is accompanied by a change in the shape of stress-strain curves, a shortening of deformation stages, a change in the hardening coefficients, and a decrease in the yield stress. It is revealed that the magnetic effects exhibit threshold behavior. The yield stress is measured as a function of the magnetic induction and the strain rate. It is established that the magnetic and electric fields have a joint effect on the kinetics of plastic deformation. A kinematic model of the macroscopic magnetoplastic effect is proposed.     

Earth optimization of space experiment on growth of germanium by floating-zone technique with the use of rotating magnetic fields

The results are considered of the earth experiments on growth of high-purity and Ga-doped germanium single crystals 15 mm in diameter and 60 mm in length, which were performed in a Zona-4 “space furnace” under the technological regimes close to those existing in space orbits. It is shown that the use of a magnetohydrodynamic (MHD) factor [weak (0.15–0.2 mT) rotational (400 Hz) magnetic fields] during crystallization of semiconductors by the floating-zone technique is a very promising method for control of dopant distributions and electrophysical properties in a growing crystal. It is shown that in such magnetic fields, the effective coefficient of Ga distribution in Ge decreases by 10%. The shift of the donor-acceptor balance of the residual dopants in a compensated semiconductor during growth with the MHD-stirring of the melt was first established in growth of undoped germanium single crystals. It was also established that magnetic fields produce different effects on the resistivity microinhomogeneity in undoped and doped crystals. The mechanisms of the MHD effect on the properties of the grown crystals are discussed as well as the perspectives of performing analogous experiments aboard spacecrafts. It is predicted that, under the microgravitation conditions, the effects revealed in terrestrial experiments would be more pronounced.     

Liquid crystal acoustics: A modern view of the problem

The main results of investigations in the fields of modern liquid crystal acoustics that originate from and continue the pioneering works of Prof. A.P. Kapustin are systematized and generalized. The following aspects of the problem are considered: acoustooptic phenomena, acoustoelectric interactions, acoustically induced domains, and effects of acoustical memory in liquid crystals. Acoustic devices based on liquid crystals are reviewed.     

Autowave model of crystal plasticity: Macro- and microdefects

A new approach to the problem of the plastic flow of solid crystals is proposed. This approach is based on studying the macroscopic localization patterns of plastic deformation, which can be considered as different types of autowave processes of defect self-organization. An unambiguous correspondence between the localization patterns and stages of plastic flow in single crystals and polycrystals is established. The propagation velocity of localized plasticity autowaves is inversely proportional to the strain-hardening coefficient, and the dispersion relation is quadratic. A new model is proposed to describe the development of plastic flow localization.     

AFM study of the surface morphology of the {100} cleavage planes of L‐arginine phosphate monohydrate single crystals

Surface morphology of the {100} cleavage planes of L‐arginine phosphate monohydrate single crystals grown from aqueous solutions is described and discussed. Different from the previous studies, dislocations are not frequently detected and most of them don't have hollow cores on the emergence points. Various step patterns are also described. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low-angle boundaries in silicon crystals

The main types of low-angle boundaries (LAB) in single crystals with diamond-type lattice are determined. The scheme of dislocation alignments formation in thermal stress field of growing crystal which allows to derive types of possible LAB and their distribution in crystal is proposed. On its basis the LAB formation in Si single crystals grown in different crystallographic directions is considered. It appears that LAB types and their distribution in the crystal depend on the character of the thermal stresses and on the crystal growth direction.     

(110) Twins of n-C28H58 crystals: Habit changes and lattice net studies

The (110) twins of normal octacosane crystals with hexagonal shape are observed. Various factors that may lead to a shape change are considered. Effect of growth rate anisotropy on the reentrent faces is studied with the help of growth patterns which are derived from a lattice net.     

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.     

In situ atomic force microscopy studies of surface morphology,growth kinetics,defect structure and dissolution in macromolecular crystallization

Surface morphologies of thaumatin, catalase, lysozyme and xylanase crystals were investigated using in situ atomic force microscopy. For thaumatin, lysozyme and xylanase crystals, growth steps having a height equal to the unit cell parameter were produced both by screw dislocations and two-dimensional nuclei. Growth of catalase crystals proceeded in alternating patterns exclusively by two-dimensional nucleation and the successive deposition of distinctive growth layers, each having a step height equal to half the unit cell parameter. The shapes of islands on successive layers were related by 2-fold rotation axes along the 〈0 0 1〉 direction. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. Growth kinetics for thaumatin and catalase crystals were investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. From the supersaturation dependencies of tangential step rates and the rates of two-dimensional nucleation, the kinetic coefficients of the steps and the surface free energy of the step edge were calculated. Adsorption of impurities which formed filaments on the surfaces of catalase and thaumatin crystals was recorded. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Crystal growth resumed upon scarring of the impurity adsorption layer and clearing of the crystal surface with the AFM tip. Adsorption of three-dimensional clusters, which consequently developed into either properly aligned multilayer stacks or misaligned microcrystals was recorded. For catalase crystals, incorporation of misoriented microcrystals as large as 50×3×0.1 μm³ produced elastic deformations in growth layers of ≈0.6%, but did not result in the defect formation. Etching experiments on catalase crystals revealed high defect densities.     

On the Contrast Zones and Strain-Induced Bands in the Hydrocarbon (n-C28H58) Crystals

Formation of contrast zones due to a phase change and occurrence of strain induced band patterns are discussed in the case of n-octacosane crystals. Slip systems are considered.     

Formation of an internal bias field in chromium-and L, α-alanine-doped triglycine sulfate crystals

The unipolar state of a chromium-and L, α-alanine-doped ferroelectric triglycine sulfate (TGS) crystal has been studied. The experimental data on the distribution of internal bias fields with respect to a seed are considered. The possible mechanisms of the formation of an internal bias field during the growth of TGS crystals with a low impurity concentration are considered.     

Nonlocal Continuum Theory of Liquid Crystals

A nonlocal continuum theory of liquid crystals is constructed to explain and predict the physical behavior of liquid crystals under long range intermolecular forces Balance laws consist of conservation of mass and mocroinertia, balance of momenta and energy. Constitutive equations are given for the equibilibirium and non-equilibirium parts of the stress, couple strees, free energy, entropy an nonlocal body force and couple. Thermodynamic restrinctions and material frame-indifference are studied. The theory is valid for liquid crystals having arbitrary shapes (inertia), Passage is made to the thread-like molecuels and to local theory. Applications are considered to two-dimensional problmes, steady, plane shear flows and disperison of twist waves.     

Studies on F-Band Absorption of Irradiated NaCl Single Crystals Excited with Laser Light

The absorption in F-band of NaCl single crystals after X-ray irradiation and later excited with laser light is studied. Similar investigations have been carried out when these crystals are subjected to high AC electric fields prior to X-ray irradiation and also at elevated temperatures. Effect of laser excitation on γ-ray irradiated samples is studied. An attempt is made to understand the results in terms of the disorder that sets in in these crystals.     

Optimization of the calculation of a local electric field in crystals by the transient-region method

The specific features of using the method of transient-region for calculating local electric fields and the corresponding potentials are considered on examples of the calculations for NaF, CsCl, and LiNbO₃ crystals. It is shown that for crystals with a primitive cubic lattice, this method can provide any given accuracy of the calculated Madelung constant; for displacive-type ferroelectrics (LiNbO₃), the method allows the calculation of the local electric field with a very high accuracy. It is emphasized that for each specific object, one has to carefully select the parameters of the convergence function.