On the inhomogeneity of the transition surface layer of the solid core of the earth

Different geophysical data and conclusions of theoretical models, which can give information about the behavior of the solid and liquid cores of the Earth as well as about the existence of a transition layer as a temperature-hysteresis region at a relatively weak first-order phase transition, are compared. It is concluded that liquid inclusions inevitably exist in this region; these inclusions are involved (due to the complex convective processes occurring in the liquid core) in the transport of light materials from some areas of the solid-core surface. The porosity and permeability of the transition layer determine the seismic acoustic inhomogeneities in these areas, which contact the convective flows in the liquid core. In particular, this explains the well-known ??east-west?? effect. Obviously, the model of the crystalline core is not the only possible alternative for a model of a core with a metallic glasslike structure.     

On the role of the porous shell of the solid core of the earth in the anomalous heat and mass flow to the mantle

The model of the pressure-induced first-order phase transition of a metal melt to the metallicglass state considers a thermodynamically nonequilibrium porous near-surface shell of the solid core of the Earth, which contacts cyclonic vortices in the liquid core. Anomalous flows of heat and light-material mass to the mantle from the solid core at these contact points are calculated. These anomalous flows are shown to be comparable with the observed ones under the assumption of a rapid increase in the melt viscosity at pressures of 1–10 Mbar, which is characteristic of a solid core. In this case, the porous layer permeability may be very low.     

Influence of the Crystal Structure of the Nucleus on the Morphology of t-ZnO Tetrapods

Crystallography Reports - A new approach to simulating the morphology of hierarchical nanocrystals has been proposed on the example of ZnO nanotetrapods. Within this approach, twinning is...     

Features of the magnetic state of the layered Fe-V nanostructure of the superconductor-ferromagnet type

The magnetic state of the V(39 nm)/20 [V(3 nm)/Fe(3 nm)] nanostructure has been investigated by polarized neutron reflectometry in the temperature range from 1.6 to 30 K in magnetic fields from 0.2 to 15 kOe. The data obtained indicate that the superconductivity of vanadium layers may affect magnetic ordering both over the depth of the structure and in its plane.     

Study of the influence of the rare-earth elements on the properties of lead iodide

Lead iodide (PbI₂) shows excellent electronic properties for detection of ionizing radiation. We report the introduction of rare-earth elements and other elements as admixtures during synthesis to study their influence on the quality of single crystals. Synthesized material as well as single crystals have been characterized by measurements of electrical resistivity and low-temperature photo luminescence and index of refraction. The structural quality with respect to polytypes was analysed by electron back scatter diffraction. Makyoh topography was applied for surface studies.     

Effect of the temperature on the TMOS sono-hydrolysis and a study of the structure of the resulting aged sonogels

The effect of temperature on the oxalic acid catalyzed sono-hydrolysis of tetramethoxysilane (TMOS) was studied by means of a heat flux calorimetric method. The activation energy of the process was measured as (24.5 ± 0.8) kJ/mol in the temperature range between 10 and 50 °C. The structural characteristics of the resulting sonogels, after long period of aging in saturated conditions, were studied by means of small angle X-ray scattering. The structure can be described as formed by ∼2.7 nm mean size mass fractal-like aggregates (clusters) of primary silica particles of ∼0.3 nm mean size, all imbibed in a liquid phase. The average mass fractal dimension of the clusters was found to be 2.58. The primary particle density was estimated as 2.23 g/cm³, in good agreement with the value frequently quoted for fused silica. The volume fraction of the clusters in the saturated sonogels was estimated as about 28%. The moment in which the meniscus of the liquid phase penetrates into the clusters under rapid evaporation process has been detected by an inflection in the first derivative of the curve of weight loss in a simple thermogravimetric test.     

A new example for the applicability of the relationship between the particle size and the kinetic of the crystal growth

Experiments have been made with PbCrO₄ precipitating system in a batch type tank. In the experiments the speeds of stirring and the residence times were changed. The particle size distribution of precipitates formed has been determined. The rate determining mechanism of the crystal growth were evaluated by two different methods (NIELSEN method and method elaborated in our institute). The two methods used have indicated the same informations about the rate determining processes. It also has been stated that the coagulation does not disturb the selection of the suitable growing mechanism.     

Ordering of cations in the voids of the anionic framework of the crystal structure of catapleiite

The pseudohexagonal crystal structure of the mineral catapleiite Na_1.5Ca_0.2[ZrSi₃(O,OH)₉] · 2(H₂O,F) from the Zhil’naya Valley in the central part of the Khibiny alkaline massif (Kola Peninsula, Russia) is studied by X-ray diffraction (XCalibur-S diffractometer, R = 0.0346): a = 20.100(4), b = 25.673(5), and c = 14.822(3) Å; space group Fdd2, Z = 32, and ρ_calcd = 2.76 g/cm³. Fluorine atoms substituting part of H₂O molecules in open channels of the crystal structure have been found for the first time in the catapleiite composition by microprobe analysis. The pattern of distribution of Na and Ca atoms over the voids of the mixed anionic framework consisting of Zr-octahedra and three-membered rings of Si-tetrahedra accounts for the pronounced pseudoperiodicity along the a and c axes of the pseudohexagonal unit cell and for the lowering of crystal symmetry to the orthorhombic one. It is shown that part of the hydrogen atoms of water molecules is statistically disordered; their distribution correlates with the pattern of the population of large eight-vertex polyhedra by Na and Ca atoms.     

Investigations of the Chemical Composition of the Metal Finds from the Levadki Necropolis

Crystallography Reports - Copper-based alloy items of the III century A.D., found in Burial no. 182 of the Late-Scythian Levadki necropolis in the submountain Crimea, have been investigated. The...     

Analysis of the Dynamics of the Controlled Crystallization Process Using the Czochralski Method

A mathematical model proposed for the Czochralski method has been employed to analyse the stability, to calculate the transitional characteristics of open and closed systems for the case that the PID control is used in the feedback circuit. The method to control the crystallization process by weighing the crystal is analysed in detail. Based on the proposed criterion of quality of the transitional process, an optimum adjustment of the controller for one- and two-channel control is performed.     

Computer Modelling of the Light Propagation through the Complex Anisotropy Systems - the way of a Determination of the Optical Parameters of the Liquid Crystal Displays

A mathematical and numerical method for an analysis of a liquid crystal displays (LCD) has been presented. The assumptions of the calculations of a light propagation through the display are shown. The real conditions of a work of these displays have been taken into account. Basing of this mathematical model a computer program for a numerical modelling of the optical parameters of LC displays working in real conditions has been worked out. This program makes possible to obtain the most important parameters of a display such as: contrast ratio, luminance in on- and off-state, spectral characteristics of light and its colour coordinates in these both states. The results obtained from this program have been verified experimentally. Very high conformity of these results has been obtained.     

Experimental Investigations of the Conditions for the Formation of the Liquid Crystalline State of Polymers

The diagrams of state for concentrated PBG solution in coordinates relating volume fraction-geometric asymmetry and volume fraction-temperature are investigated. The order parameter for macromolecules in the anisortropic phase is dettermined. The experimental data compare with the existing theoretical models for th formation of the liquid crystalline state in solutions of stiff polymer molecule. It is shown that experimental data are in good quantitative agreement with the Flory's lattice model.     

The influence of the d-core states on the calculation of the crystal structure of Zn with the optimized model potential

Shaw model potential has been used to calculate the structural energies of Zn using different model potential parameters. The effects of changing the model potentials, of using energy-wavenumber characteristics calculated with intervals of q/2k_F = 0.05 and 0.025, and of using different interpolation methods on the structural energies are investigated.     

On the Influence of the Crystallization Conditions on the Microstructure of the Directionally Solidified Eutectic of the LiF – LiYF4 System

This paper particularly deals with the transitions in degree and type of ordering of a given microstructure. As a model system the eutectic of the LiF – LiYF₄ system was used for studies of transitions from ‘anomal’ microtextures with non-cooperative production of seeds of both phases to the fibrous microtexture. It was shown that even if the matrix phase LiYF₄ contains a relative high volume ratio (36%) of LiF it is possible to create highly ordered fibrous microtextures with pronounced hexagonal ordering of particular LiF fibres. It was also shown that methods of image processing could be used for sensitive evaluation of small changes in degree of ordering of the microstructure. These procedures make possible a deeper understanding of the influence of the solidification conditions on the microstructure of the directionally solidified eutectic and creates possibilities for optimalisation of the technological process.     

On the 70th anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences

We are celebrating the 70th anniversary of the Shubnikov Institute of Crystallography. The institute has gone from being a small laboratory of piezoelectric crystals to a large internationally known scientific center. The 1990s was a decade of ruin, both literally and figuratively, for our institute; however, it is hard to believe that was the case when walking through the corridors of the institute today.     

Madelung constants of the superlattices of the laves phases

The Madelung constants of all possible superlattices of the Laves phases are calculated using a modified form of the Ewald-Fuchs method.     

Determination of Physical Constants of the Melt and the Parameters of the Control Object Concerning Crystal Growth from the Melt

New Techniques are presented for the determination of the capillary constant and the coefficient of thermal expansion of the melt using an electrocontact sensor (ECS). The density of the melt, the capillary constant, the coefficient of the thermal expansion of the melt, the growth angle, and the characteristic time of thermal relaxation of the thermal zone are determined for the case of growing the lithium niobate crystals by Czochalski technique.