Parity violation and parity conservation in unstirred crystallization: Effect of first crystals

Statistics of nucleation of chiral forms was studied to establish the effect of the number of first crystals and their handedness on distributions of enantiomers. Various bimodal, trimodal and unimodal distributions are obtained in unstirred crystallization, depending on the number of initial crystals and growth conditions. The binomial distribution satisfactorily describes experimental distributions of enantiomeric excess and may be used to predict distributions and probabilities of nucleation of enantiomers. The first nucleated crystals determine the handedness of secondary crystals, and number of initial crystals governs statistics of chiral nucleation. According to the binomial distribution if single crystals nucleate as the first, the bimodal distributions result with D and L peaks. If LD, LL, and DD pairs are nucleated as first, trimodal distributions with D, R, and L peaks are created, and if groups of crystals of various handedness nucleate as the first the unimodal distributions of enantiomeric excess with racemate R peaks are formed. Chiral nucleation experiments on sodium bromate were the basis for the theoretical considerations and verifications of predictions resulting from binomial distributions on probabilities of the creation of L and D crystals, and racemates, and the presence of D, L, and R peaks in the distributions. Growth conditions affect the number of the first crystals and effectiveness of cloning, and as a result, the distributions of enantiomers. Formation of pure enantiomers and/or racemates proves that the conservation of chiral symmetry, and the breakage of chiral symmetry can occur in unstirred crystallization. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of temperature fields in doped anisotropic crystals under spatially inhomogeneous light beams passing through them

The features of formation of thermal fields in potassium dihydrophosphate crystal doped with potassium permanganate under a 532-nm laser beam passing through it have been investigated. Data on the influence of birefringence on the temperature distribution in an anisotropic crystal whose surface is illuminated by a spatially modulated light beam are presented.     

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.     

Methods for measuring light scattering in germanium and paratellurite crystals

Methods for studying the scattered light in germanium and paratellurite (α-TeO₂) crystals are considered. Investigations of the light scattering in Ge crystals were performed in the infrared wavelength range by the photometric-sphere method (in the range 2–3 μm) and by measuring the line-scattering functions (at 10.6 μm). In the visible range, the paratellurite single crystals were investigated by recording and analyzing images of laser beams transmitted through the samples. It is shown that small-angle Mie scattering is characteristic of both materials. Some conclusions about the sizes and the physical nature of scattering inhomogeneities are drawn. The effect of high-temperature annealing on the scattering intensity is studied.     

Low-frequency phonon dynamics,spin-lattice relaxation,and sound attenuation in crystals with incommensurate phases

Specific features of the low-frequency response of a phason and an amplitudon in the region of small wave vectors are considered in incommensurate displacive-type phases at high and low temperatures. The corresponding anomalies of spin-lattice relaxation (SLR) rate and attenuation of the longitudinal sound in the vicinity of the normal phase transformation into an incommensurate phase are analyzed. It is shown that the divergence of the amplitudon response at small wave vectors and low frequencies induced by the interaction with phasons clearly manifests itself only at low temperatures T and that the pronounced amplitudon contribution proportional to T³ to the SLR rate is associated with this divergence. The phason-response divergence at low temperatures leads to the frequency-independent contribution proportional to T to the SLR rate.     

Hydrothermal growth of crystals under visual examination

Hydrothermal growth, recrystallization and synthesis of -TeO₂. Te₆O₁₁C₁₂, CuBr, PbI₂, PbBr₂, PbCl₂ SbNbO₄ monocrystals in an apparatus with visual examination are considered. In the apparatus with an optical quartz reactor the experiments were carried out to study the hydrodynamics of the solution in the homogenous and binary phase gas-liquid media. The data obtained agree well with those calculated thus permitting us to take into account the effect of hydrodynamical environment on supersaturation and mass transport kinetics. This fact was demonstrated while studying kinetics of mass transport of -TeO₂ on seeds in homogenous and binary phase gas liquid media. Solubility of TeO₂ monocrystals and kinetic properties of their growth were studied in their dependences on physical, chemical and hydrodynamical parameters and the growth mechanism was suggested. Simultaneous growth of tellurium dioxide and oxychloride monocrystals was first observed in the system TeO₂-HCl-H₂O in homogenous and binary phase solutions, the corresponding dependences on temperature, temperature gradient and HCl concentration have been analyzed. The mechanism of simultaneous growth of these crystals and its relationship with the composition of the crystallization medium are considered. The apparatus with visual examination was demonstrated to be useful in the synthesis and recrystallization of PbHal (Hal = I, Br, Cl) monocrystals under various PT conditions.     

Influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light in biaxial crystals

The influence of the antisymmetric part of gyration pseudotensor on the characteristics of transmitted light have been investigated for biaxial crystals. Analytical expressions for the optical rotation in the direction of optical axis are obtained with allowance for both the symmetric and antisymmetric parts of gyration pseudotensor. The polarization azimuth and transmitted light ellipticity have been calculated at different angles of incidence.     

The influence of optical activity on the intensity and polarization parameters of transmitted light in crystals

The ellipticity and azimuth of light transmitted through an optically active plate and the intensity of this light transmitted through an analyzer are theoretically investigated as functions of the rotation angle of the plate. Relationships describing these parameters are considered. It is demonstrated that, depending on the angle of inclination of the plate, the optical activity can affect the characteristics of the transmitted light differently. A technique for determining the optical activity parameters is proposed from analyzing the relationships for the light intensity. The conoscopic figures of uniaxial and biaxial optically active crystals are described.     

Infrared light scattering and absorption microscopy investigations at dislocations in GaAs crystals

In recent years a number of experiments have been published dealing with the light scattering at small particles. All of these experiments have been made in the visible spectral range. In this paper we report an experimental arrangement for infrared light scattering by dark-field illumination. Preliminary results of the observations of dislocations in GaAs crystals are given. The scattering images are correlated with results obtained by means of absorption microscopy with infrared light. Helix-like fine structures of dislocations are found mainly arranged in the 〈110〉 directions.     

Polarization distribution in DTGS crystals under nonequilibrium thermal conditions

The polarization distribution in crystals of deuterated triglycine sulphate in a constant temperature gradient is investigated on the basis of the dynamic method for studying the pyroelectric effect. It is shown that, under equilibrium thermal conditions, the polarization distribution is uniform except for the surface layer ～20-μm-thick. The nonuniform polarization distribution in this layer may indicate its multidomain state. In a steady-state temperature gradient, the layer thickens and its domains grow into the sample bulk.     

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.     

Autodeformation bending of gypsum crystals grown under the conditions of counterdiffusion

The dynamics and kinetics of growth-induced bending of gypsum crystals grown from solution have been studied. Crystallization was performed by the method of chemical reaction under the conditions of component counterdiffusion. It is established that autodeformation bending occurs in the [001] direction at the growth front and is caused by cationic impurities. The crystal curvature depends on the anisotropy of growth rate and increases at lower supersaturations. The mechanism of growth-induced crystal bending is suggested which takes into account the heterometry stresses providing the appearance of a bending moment at the growth front.     

Compensation for the spectral dispersion of light polarization states in electro-optic modulators based on chiral liquid crystals

The effect of compensation for the spectral dispersion of light polarization states at the output of a single-domain layer of a chiral liquid crystal (CLC) is experimentally studied. It is shown that such dispersion can be decreased significantly with the aid of phase plates of two types that have different signs of the spectral dispersion of birefringence. The dispersion compensation allows one to significantly increase the operating spectral range of fast light modulators based on chiral nematic liquid crystals (NLCs).     

Changes of the growth morphology in insb crystals pulled under the presence of ultrasonic vibrations

In the Czochralski method, the effect of ultrasonic vibrations on the growth of InSb single crystals was investigated by observing the growth morphology. Remarkable changes which ultrasonic vibrations brought about were: (1) the crystal diameter, (2) the width of the facet region and (3) the inclined angle of non-facet interfaces near the facet region for the (111) plane. After introducing vibrations, the crystal diameter decreased smoothly with growth time. However, both the facet width and the inclined angle reached each minimum value after 5 to 7 min regardless of the magnitude of vibrational output powers from 30 to 90 W, and they were in roughly proportional relation with each other. The change rates of crystal diameter and of facet width increased with vibrational powers. The decrease of crystal diameter was known to result from the rise of the melt temperature, which was brought by both the mixture of the melt and the thermal energy transformation due to ultrasonic vibrations. The change of facet width depended upon the melt flow itself in addition to the temperature rise.     

Morphology of gallium orthophosphate crystals grown under hydrothermal conditions

Gallium orthophosphate crystals with sizes of 5 mm and more have been obtained by spontaneous nucleation from hydrothermal 5.6 – 15 M orthophosphoric acid solutions. Preferable concentrations of solvent were found in the range of 11 – 12 M, the temperature difference should not be over 6–10°C at the heating rate of 4 – 5 °C/day. Morphological investigations are carried out using optical and polarizing microscopies. GaPO₄ crystals, like quartz and berlinite, tends to grow with well developed {1 1}, {0 1}, {1 0}, {1 2}, and {0 2} faces, and they were divided into three habit types. Effect of orthophosphoric acid concentration on the crystal habit has been studied.     

Bidomain structures formed in lithium niobate and lithium tantalate single crystals by light annealing

The bidomain structures produced by light external heating in z-cut lithium niobate and lithium tantalate single crystals are formed and studied. Interdomain regions about 200 and 40 μm wide in, respectively, LiNbO₃ and LiTaO₃ bidomain crystals are visualized and studied by optical microscopy and piezoresponse force microscopy. Extended chains and lines of domains in the form of thin layers with a width less than 10 μm in volume, which penetrate the interdomain region and spread over distances of up to 1 mm, are found.     

Mutual transformation of light waves by reflection holograms in photorefractive crystals of the $$\bar 43m$$ symmetry

The mutual transformation of light waves in the case of their simultaneous diffraction from a bulk reflection phase hologram, which was formed in a cubic photorefractive crystal of the [`4]3m\bar 43m symmetry class, has been studied. The indicator surfaces of the polarization-optimized values of the relative intensity of the object wave, which make it possible to determine the amplification of this wave for any crystal cut, are constructed. The linear polarization azimuths at which the energy exchange between the light waves reaches a maximum are found numerically for crystals of different cuts.     

Study of the possibility of growing germanium single crystals under low temperature gradients

The possibility of growing germanium single crystals under low temperature gradients in order to produce a dislocation-free material has been studied. Germanium crystals with a dislocation density of about 100–200 cm^?2 have been grown in a system with a weight control of crystal growth at maximum axial gradients of about 1.5 K/cm.     

X-ray diffraction study of crystals under a static electric field

This paper gives an overview of the effect of electric field on the diffracted intensity and contrast on the X-ray topographs recorded from crystals of non-linear and electro-optic materials, ionic conductors, semiconductors, insulators and ferro-electric materials. Application of a dc electric field gives rise to a change in the diffracted intensity by several orders of magnitude and contrast on the topographs. The effect is illustrated with examples of -LiIO₃, KTiOPO₄, LiN₂H₅SO₄, KNbO₃, LiNH₄SO₄, quartz, silicon etc. and the mechanism for it is discussed.