Crystallographic table of chemical elements

Regularities of changes in the structure of chemical elements in crystalline and liquid states under the action of temperature and pressure are systematized on the basis of the periodic table.     

Heat-resistant metals in Mendeleev’s periodic table

The data from the Inorganic Crystal Structure Database (ICSD, version 1.7.1, 2010?C2) on refractory elements of Mendeleev??s periodic table have been analyzed. Insight is gained into the current state of structural studies of simple materials, the number of polymorphs, and their symmetry.     

On the elements of the dislocation structure of deformed corundum

It is found by the method of transmission electron microscopy that the main elements of dislocation structure of deformed corundum are spatial triple dislocation nodes, recombination zones and dislocation network fragments. The structure of dislocation nodes is analyzed. It is shown that the nodes in corundum are the “rigid” constructions.     

Spectrum of natural electromagnetic waves in a periodic ferromagnet-dielectric structure

The specific features of propagation of natural TE waves in a periodic ferromagnet-dielectric structure are investigated in the following geometry: a bias magnetic field is parallel to the ferromagnet/dielectric interface and perpendicular to the wave propagation direction. The transformation matrix for the period of the structure, the dispersion relation, and the energy reflection coefficient are obtained for the case of normal incidence of a wave on a semi-infinite periodic medium by solving the boundary-value problem. It is shown that an external field can be used to control the spectrum and characteristics of reflected waves.     

Hysteresis loops of a periodic multilayered structure with antiferromagnetic coupling

The hysteresis loops of 18° in-plane magnetization reversal in a system of magnetic films with cubic crystallographic anisotropy coupled by the interlayer antiferromagnetic exchange interaction are plotted. The loops correspond to different orientations of the switching field with respect to crystallographic axes. Wasp-waisted loops, loops collapsing in weak fields, and bistable (bifurcation) loops are found.     

Simple criterion of division of two-dimensional space of a periodic lattice into arbitrarily shaped polyominoes

The method of discrete modeling of molecular packings in crystals is further developed. A criterion of the translational division of the two-dimensional space into arbitrarily shaped polyominoes based on the comparison of the vector systems of the polyomino points with the points of the packing multispace is suggested. The analysis of the properties of this multispace has been performed for the first time in the present study.     

Threshold spatially periodic structure of the director in a nematic flexoelectric cell with finite anchoring energy

The influence of the finiteness of the anchoring energy of a director and the value of flexoelectric polarization on the threshold of a spatially periodic reorientation of the director and the period of the arising structure is considered for a planar nematic cell. The threshold and the period are calculated numerically and the corresponding analytical expressions are obtained for the case of a strong anchoring of the director. It is shown that for a finite azimuthal anchoring energy the range of admissible values of the flexoelectric parameter ν widens, while for a finite polar anchoring energy this range narrows as compared to the case of an absolutely rigid orientation of the director at the cell surface.     

Study of the chemical reactions' influence on semiconductor films structure formation by the Monte-Carlo method

The investigation by the Monte-Carlo method of the growth of the silicon epitaxial film at a chloride CVD system has allowed to find out the composition of adsorption layer, the micromechanism of the reactions of Si atoms building-in into the growing crystalline layer and the growth conditions influence on the growth rate and film surface roughness. The change of adsorptive layer composition in the system SiCl₄—HCl—H₂ (fraction of adaatoms, silicon atoms built-in a crystal and molecules SiCl₂) depending on temperature has been determined. The change of silicon film growth rate depending on temperature and concentration change of SiH₂Cl₂ has been established and the contribution of growth mechanism (with participation of adatom, silicon atoms and molecules SiCl₂) into the total rate of film growth has been shown.     

Observation of the periodic fluctuant dendritic structure in an Al–38 wt% Cu hypereutectic alloy processed by ACRT-B method

The microstructure of periodic fluctuant dendritic θ in a matrix of +θ eutectic was obtained in an Al–38 wt% Cu alloy processed by ACRT-B method grown at growth velocities (V) ranging from 5 to 60 μm/s and crucible rotating in a trapezoidal way with maximum rotation rates (Ω_max) ranging from 100 to 400 rpm. Formation of this structure is explained by the influence of the periodical Ekman flow on the growth of dendritic θ during the spin-up and spin-down process. It was also observed that the +θ eutectic between the primary dendrites of θ (CuAl₂) is not periodic and fluctuant during ACRT-B process. This is quite different from our previous observation of periodic eutectic in Al–Cu eutectic processed by similar ACRT-B method.     

Investigation of the structure of solid solutions of elements of the IV. group (Si,Ge) in gallium antimonide

Precision measurements of the lattice parameter and the density of Si- and Ge-doped GaSb monocrystals were accomplished. The investigated crystals were Czochralski-grown from an equiatomic melt (with respect to its own components) and doped with 2 · 10¹⁷ to 4 · 10¹⁹ cm^–3 Si and 2 · 10¹⁷ to 4 · 10¹⁹ cm^–3 Ge, respectively. The concentrations of the dopants were determined spectroscopically. — Hall measurements at room temperature showed that Si as well as Ge in GaSb produce p-conduction.     

Evolution of chemical structure during silver photodiffusion into chalcogenide glass thin films

The change of chemical structure resulting after X-ray and photo-induced silver diffusion into chalcogenide glass (ChG) thin films is monitored by high resolution X-ray photoelectron spectroscopy (XPS). As₄₀S₆₀ and Ge₃₀Se₇₀ thin films, which are based on pyramids and tetrahedral structural units, are investigated as model materials. Survey, core level (As 3d, S 2p, Ge 3d, Ge 2p, Se 3d, Ag 3d_5/2, O 1s, C 1s) and valence band spectra have been recorded and analyzed. Reference point for the binding energy is established by the subsequent deposition of thin gold film on top of the measured samples. The chemical structure gradually changes during diffusion of silver in all the samples. The mechanism of change depends on the chemical composition, thickness of the diffused silver layer and conditions of irradiation. It is revealed that surface oxygen can play important role in the Ag photodiffusion process, leading to phase separation on the surface of the films. Photodiffusion of Ag into As₄₀S₆₀ film leads to the formation of a uniform ternary phase and arsenic oxides on the surface. The formation of ethane-like Ge₂(S_1/2)₆ units together with germanium oxidation are the main outcomes of X-ray induced Ag diffusion into Ge₃₀Se₇₀ film.     

Selective optical properties of a multilayered periodic gyrotropic structure at an arbitrary angle of incidence of waves

A multilayered periodic gyrotropic structure consisting of an arbitrary number of unit cells is considered. The gyrotropic properties of this multilayered structure are due to the external magnetic field. A matrix is calculated on the basis of the boundary conditions for waves in each layer, which relates a wave incident at an arbitrary angle with the transmitted and reflected waves. The complex amplitude transmittance and reflectance are found for the entire multilayered structure from the calculated matrix elements. The optimal parameters of a structure consisting of layers of potassium dihydrogen phosphate and europium-doped glass are calculated. The dependences of the intensity, ellipticity, and the angle of rotation of the major axis of the polarization ellipse of reflected and transmitted waves on the number of cells, light frequency, and magnetic field at an arbitrary angle of incidence of waves are obtained in graphical form. The structure considered is characterized by selective reflection of electromagnetic waves and can be used as a polarization converter controlled by a magnetic field.     

Influence of the chemical nature of implanted ions on the structure of a silicon layer damaged by implantation

The influence of the implantation of silicon single crystals by fluorine, nitrogen, oxygen, and neon ions on the distribution of strain and the static Debye-Waller factor in the crystal lattice over the implanted-layer depth has been investigated by high-resolution X-ray diffraction. The density depth distribution in the surface layer of native oxide has been measured by X-ray reflectometry. Room-temperature implantation conditions have ensured the equality of the suggested ranges of ions of different masses and the energies transferred by them to the target. It is convincingly shown that the change in the structural parameters of the radiation-damaged silicon layer and the native oxide layer depend on the chemical activity of the implanted ions.     

The P\bar 1 space group changes in journal of crystallographic and spectroscopic research and in journal of chemical crystallography

The crystal structures of seven compounds, originally described in the centrosymmetric triclinic space group (No. 2), have been revised to centered monoclinic. Six are now described in space group No. 15 (C2/c or I2/a) and one in space group No. 12 (C2/m). Three structures (TADTEX, VICHIY, YAWZUR) have been re-refined in the correct space group. For six instances the decrease in symmetry results in only minor adjustments and the structure is essentially correct as it is expected when the original and the revised space groups are both centrosymmetric. However, in one instance (VICHIY) the reformulation in the higher space group changes (unexpectedly) the molecular dimension as much as 0.12 Å, even if the space group change is between two centrosymmetric space groups (from to C2/c). This was attributed to the easy decomposition of the crystal. The percentage of revised crystal structures was found to be 1.71%, namely 8 on a total of 467 analyzed structures. A low value if compared to the 3% value found by Marsh and Spek for C2 space group.     

Crystal structure of tveitite-(Y): Fractionation of rare-earth elements between positions and the variety of defects

The crystal structure of the mineral tveitite-(Y) (Y_0.883Na_0.106) (Ca_0.841 LREE _0.159)(Ca_0.716Na_0.204 HREE _0.080)(Ca_0.092Na_0.074)F_6.952 from amazonite pegmatites of Rov-Gora Mountain (Keivy, Kola Peninsula) is determined using X-ray diffraction (Stoe IPDS diffractometer, λMoK _α, graphite monochromator, 2θ_max = 63.5°, R = 0.051 for 1542 reflections). The main crystal data are as follows: a = 17.020(2) Å, c = 9.679(2) Å, V = 2428.2(4) ų, space group $R\bar 3$ , Z = 18, and ρ_calcd = 4.00 g/cm³. The idealized structural formula of the mineral is represented as (Y,Na)₆(Ca,LREE)₆(Ca,Na,HREE)₆(Ca,Na)F₄₂ (Z = 3). The defect structure of the mineral manifests itself in a mixed occupation of all four independent cation positions and in a randomly disordered distribution of fluorine atoms over the majority of anion positions. It is shown that the crystal structure of tveitite-(Y) fulfills the function of an “Eratosthenes sieve” for yttrium cations and two groups of lanthanide cations, so that these cations are distributed over three different positions.     

Observation of chemical reaction and liquid structure of SGe by Raman spectroscopy

The measurements of the Raman spectra on liquid Ge_XS_1?X (0≤X≤0.1) were carried out. The A₁ mode of $\text{GeS}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ (ca. 340 cm^?1) was observed in the liquids. The comparison with the spectra of liquid S suggests that Ge reacts on the polymeric species. During the chemical reaction of solid Ge and liquid S below ca. 500°C, the L.T.GeS₂ crystal growth was observed. The spectral features of the L.T.GeS₂ surprisingly resemble those of GeS glasses. The glass forming region was extended to X = 0.03 by careful rapid quenching. The overall compositional dependence of the Raman spectra of Ge_XS_1?X (0.03≤×≤0.341) was analysed in comparison with the spectra of the L.T. and the H.T. crystal and can be explained by the model that with increase of X(>ca. 0.2) the H.T. GeS₂-like spectra emerge abruptly from the L.T.GeS₂-like spectra in lower X. Standing on the model, the glassy structures in this system are discussed.     

Factors influencing the periodic precipitation of BaMoO4 crystals in silica gel

Influence of electric and magnetic fields on the periodic precipitation of BaMoO₄ crystals in Silica gel has been discussed. The retarding effect of gel density on the advancing precipitation front has been qualitatively analysed. The role of impurity on the formation of rings has been investigated.     

Effects of modifier additions on the thermal properties,chemical durability,oxidation state and structure of iron phosphate glasses

Modified iron phosphate glasses have been prepared with nominal molar compositions [(1?x)·(0.6P₂O₅–0.4Fe₂O₃)]·xR_ySO₄, where x = 0–0.5 in increments of 0.1 and R = Li, Na, K, Mg, Ca, Ba, or Pb and y = 1 or 2. In most cases the vast majority or all of the sulfate volatalizes and quarternary P₂O₅–Fe₂O₃–FeO–R_yO_z glasses or partially crystalline materials are formed. Here we have characterized the structure, thermal properties, chemical durability and redox state of these materials. Raman spectroscopy indicates that increasing modifier oxide additions result in depolymerization of the phosphate network such that the average value of i, the number of bridging oxygens per –(PO₄)– tetrahedron, and expressed as Qⁱ, decreases. Differences have been observed between the structural effects of different modifier types but these are secondary to the amount of modifier added. Alkali additions have little effect on density; slightly increasing T_g and T_d; increasing α and T_liq; and promoting bulk crystallization at temperatures of 600–700 °C. Additions of divalent cations increase density, α, T_g, T_d, T_liq and promote bulk crystallization at temperatures of 700–800 °C. Overall the addition of divalent cations has a less deleterious effect on glass stability than alkali additions. ⁵⁷Fe Mössbauer spectroscopy confirms that iron is present as Fe²⁺ and Fe³⁺ ions which primarily occupy distorted octahedral sites. This is consistent with accepted structural models for iron phosphate glasses. The iron redox ratio, Fe²⁺/ΣFe, has a value of 0.13–0.29 for the glasses studied. The base glass exhibits a very low aqueous leach rate when measured by Product Consistency Test B, a standard durability test for nuclear waste glasses. The addition of high quantities of alkali oxide (30–40 mol% R₂O) to the base glass increases leach rates, but only to levels comparable with those measured for a commercial soda-lime-silica glass and for a surrogate nuclear waste-loaded borosilicate glass. Divalent cation additions decrease aqueous leach rates and large additions (30–50 mol% RO) provide exceptionally low leach rates that are 2–3 orders of magnitude lower than have been measured for the surrogate waste-loaded borosilicate glass. The P₂O₅–Fe₂O₃–FeO–BaO glasses reported here show particular promise as they are ultra-durable, thermally stable, low-melting glasses with a large glass-forming compositional range.     

Optimization of the local crystallization processes of preparing chiral drugs in periodic crystallizers

The regularities of periodic processes of local crystallization of enantiomers and the kinetics of nucleation and growth of crystals are considered. The criteria for optimization of technological processes of preparing chiral drugs with the aim of attaining the maximum yield of final products with a required optical purity are formulated on the basis of experimental data.     

Local 3D real space atomic structure of the simple icosahedral Ho11Mg15Zn74 quasicrystal from PDF data

We present a new complementary strategy to quasicrystalline structure determination: The local atomic structure of simple icosahedral (si) Ho₁₁Mg₁₅Zn₇₄ [a(6D) = 5.144(3)Å in a sphere of up to r = 17Å was refined using the atomic pair distribution function (PDF) from in‐house X‐ray powder diffraction data (MoKα₁, Q_max = 13.5Å⁻¹; R = 20.4%). The basic building block is a 105‐atom Bergman‐Cluster {Ho₈Mg₁₂Zn₈₅}. Its center is occupied by a Zn atom – in contrast to a void in face centred icosahedral (fci) Ho₉Mg₂₆Zn₆₅. The center is then surrounded by another 12 Zn atoms, forming an icosahedron (1st shell). The 2nd shell is made up of 8 Ho atoms arranged on the vertices of a cube which in turn is completed to a pentagon dodecahedron by 12 Mg atoms, the dodecahedron then being capped by 12 Zn atoms. The 3rd shell is a distorted soccer ball of 60 Zn atoms, reflecting the higher Zn content of the si phase compared to the fci phase. In our model, 7% of all atoms are situated in between the clusters. The model corresponds to a hypothetical 1/1‐approximant of the icosahedral (i) phase. The local coordinations of the single atoms are of a much distorted Frank‐Kasper type and call to mind those present in 0/1‐Mg₂Zn₁₁. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)