Influence of TM and RE elements on glass formation of the ternary Al-TM-RE systems

The effects of TM and RE elements on glass formation ability (GFA) of the Al-TM-RE systems are studied systematically. The TM elements show distinct differences: critical sizes of the Al-TM-Ce systems are in the order of Ni > Co > Fe > Cu. However, the RE elements show similar effect on glass formation. These results are discussed in terms of the GFA-related factors, i.e., reduced glass transition temperature (T_rg = T_g (T_x)/T_L, where T_g, T_x and T_L are the glass transition temperature, onset crystallization temperature and liquidus temperature, respectively) and the mixing enthalpy ΔH_Al-TM. A new parameter of T_L − T_g (T_x) is potentially proposed and used to evaluate the GFA of the Al-based alloys, as well as bulk glass-formers.     

Prospective evaluation of the use of various materials as matrices for active elements of lasers

Methods of prospective evaluation of the use of various materials as active elements for quantum generators for certain applications are considered. The way of evaluation for all kinds of dielectric crystal lasers with respect to optical quantum generators, applicable in technical designs is given. The influence of material properties on the prospective technical use is considered. The results are summarily analyzed.     

Electrical elements of the optical systems based on hydrogel - electrochromic polymer composites

Abstract

The results of studies of the electrically controlled elements of optical systems based on hydrogel - electrochromic polymer with conjugated π-electron system are shown. One important feature of conjugated polymers is the ability to change their optical characteristics under an external electric field. The electrochromic effect of these polymers may find applications in optical gating and filtering systems, optical sensors, ‘‘smart windows’’, optical memories, IR-switching, and electrochromic displays. Such electrochromic polymers were embedded in the matrix of a macroporous polymer hydrogel by the oxidative chemical polymerization method. The obtained samples based on hydrogel - polyaniline and hydrogel - polyorthotoluidine composites demonstrate the electrochromic behavior. In these composites, the electrolyte, as well as the electrochromic polymer, are located directly in the volume of hydrogel.     

Internal friction data as explained on the basis of structural-energetic parameters of inorganic glasses

On the basis of a previously reported model the diffusive mechanism of internal friction in microheterogeneous inorganic glasses is discussed. A method of calculating the activation energy, the dimensions of the structure complexes and defects, as well as the masses of relaxing structure elements is proposed. The potentialities of the method for a series of binary and ternary alkali-silicate glasses are shown.     

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.     

Different morphologies of the dry physical gels as a function of the sample preparation method

Xerogels obtained by drying the gels formed by glucofuranose derivatives with organic solvents were studied. The xerogels were characterized using the SEM, XRD, DSC and OPM techniques. The morphology of a xerogel observed by SEM may change from ‘amorphous, fibrillar’ to ‘crystal-like’, which may be caused by time or temperature. The results suggest that a similar transition may take place when the xerogel is being prepared. Thus SEM pictures of xerogels should be treated with great caution as they may not reflect the gelator network morphology in the bulk gel.     

Comments on the structure of copper (II) oxalate: Discussion of X-ray powder diffraction and EXAFS results as a basis for the interpretation of magnetic properties

Some features of the crystal structure of Cu(II) oxalate, which are relevant for the interpretation of unusual magnetic properties of the substance, are discussed. EXAFS and X-ray powder diffraction results described by different authors are compared. The results of both the analytical methods complement each other. The packing of the ribbon-like structural units consisting of Cu²⁺ and (C₂O₄)²⁻ ions is demonstrated. It is shown that the Cu ions are octahedrally coordinated by O atoms (four short and two long Cu-O distances). The environment of a central Cu ion with other Cu ions is discussed in terms of intra- and inter-ribbon distances. In view of the structural characteristics of Cu(II) oxalate it seems to be not justified to disregard the interaction between neighbouring ribbons in the discussion of the magnetic coupling, as done so far.     

Heterogeneous equilibria and distribution of elements in the MCVD process for making optical fiber

Thermodynamic calculations have been performed on systems relevant to doped silica optical fiber processing: SiCl₄---GeCl₄---POCl₃---O₂, SiCl₄---BBr₃---O₂, O₂---H₂O---CH₄---SOCl₂---SiO₂ and O₂---H₂O---CH₄---CF₄---SiO₂ by using the SOLGASMIX-PV computer program. Equilibrium distributions of Ge, P, Si, B and H species are given.     

On modifications of the well-known Hume-Rothery rules: Amorphous alloys as model systems

Structure formation in condensed matter physics is still far from being understood. One important approach, for a limited class of systems selected by some exclusion rules, goes back to Hume-Rothery. Here we review on measurements of the static structure, electronic properties, and the thermal stability of amorphous TM-Al (TM: Ti, V, Cr, Mn, Fe, Co, Ni) and Na–Sn alloys. Concluding from the results, we postulate that the Hume-Rothery rules can be lifted in some cases, extending the Hume-Rothery scheme, i.e., the opening of band gaps at the Fermi energy, to a much wider class of materials, making it more general.     

3D printed models of small and large molecules,structures and morphologies of crystals,as well as their anisotropic physical properties

Three‐dimensional (3D) physical models of atomic structures of crystals, their anisotropic properties and morphologies as well as models of small and large molecules were printed with support from 3D Systems Corporation. Structural information in Crystallographic Information Framework (CIF) files from the Crystallography Open Database and the Protein Data Bank was utilized. Computer programs were either newly developed (Cif2VRML) or enhanced by 3D print file export functions (WinXMorph and WinTensor) in order to design most of these models. Current 3D printing technologies are briefly reviewed. The literature on the impact on students’ comprehension and retention of structural information with access to such models is assessed. Our taking of a historical perspective in this paper illustrates that the usage of models has for more than 200 years been an integral component of crystallography.     

Reflectometer for studying the surface of liquid systems

To study the free surface of liquids, a Reverans reflectometer with a vertical neutron scattering plane has been designed and is fabricated at Petersburg Nuclear Physics Institute. This reflectometer is intended to investigate surfaces and interfaces in liquid magnetic or nonmagnetic systems. The principles of reflectometer operation are described. The general view of the reflectometer with ready units is presented and its main technical parameters are given. The results of preliminary tests are reported.     

Undulator systems and photon diagnostics for the European XFEL project

For the European XFEL project very long undulator systems are required. Due to the nature of the SASE process there are stringent requirements and tolerances on these systems. An extensive R&D phase to solutions has been started. In this contribution an overview over this R&D work is given.     

Studies of structures and properties of polymeric systems containing bis-(hydroxy-arylidene)alkanones as NLO-active chromophores

NLO-properties of polymer systems containing bis-(hydroxy-arylidene)alkanone chromophores were studied experimentally and analyzed using ab initio quantum chemical calculations. A monoclinic crystal structure (space group P2₁11) of the polyester containing fragments of such chromophores in the backbone was simulated and a reasonable agreement between the experimental and simulated X-ray powder diffraction patterns was achieved. Ab initio quantum-mechanical estimations of the SHG-observable macroscopic second-order non-linearity tensor coefficients, obtained for the polymer crystal structure at the HF SCF level, led to the major d_XZZ-coefficient of 1.9 pm/V. Films of ionic complexes of strongly basic poly-1,10-decamethylene-acetamidine with various bis-(hydroxy-arylidene)alkanone chromophores were prepared and shown to display considerable THG-efficiencies. The molecular structure of these complexes is discussed on the basis of the experimental spectroscopic data and calculated relative stabilities of different forms of the complexes. The formation of the complexes results in a considerable increase of the glass transition temperature by ≈70°C.     

New flux systems for the LPE growth of thin garnet films

A new flux system is presented for the growth of bismuth substituted iron garnet thin films by liquid phase epitaxy. The fluxes do not contain lead and are based on the system Bi₂O₃, RO₂ where R = Si, Ge, Ti or Ce. Data is presented that shows the viscosities of these melts are below 16 cp at temperatures ∽800°C when the eutectic compositions are chosen and that they have low freezing points. The growth conditions and melt compositions are given for the growth of various rare-earth iron garnets with high bismuth substitutions. Results of measurements of optical and magnetic properties of some of the from Pb containing fluxes. Thus these materials are more promising for use in magnetic bubble displays. It is also shown that the uniaxial anisotropy was also less in the films grown from the new system than those grown from Pb containing fluxes.     

Modification of the malus law for the torsional deformation of lyotropic nematics in magnetic field on the basis of statistical approach

A method based on the statistical approach is proposed to calculate the light intensity for the torsional deformation of lyotropic nematic liquid crystals at violated Mauguin adiabatic approximation. Theoretical dependences of the light intensity on the magnetic field strength are obtained for two limiting cases of lyotropic nematic anchoring with bearing surfaces: infinite and low anchoring energies.     

On the role of rotating tetrahedra for generating auxetic behavior in NAT and related systems

Systems with negative Poisson’s ratios (auxetic) exhibit the unexpected feature of expanding laterally when uniaxially stretched and becoming narrower when compressed. Here, we examine the role of the tetrahedra found in the frameworks of the predicted auxetic zeolites natrolite (NAT), thomsonite (THO) and edingtonite (EDI) for generating negative Poisson’s ratios in an attempt to relate the auxeticity in the (0 0 1) plane to rotations of the tetrahedra in the zeolite framework. The behavior of the tetrahedra is then examined in terms of their 2D projections in the (0 0 1) plane and we show that in the extreme scenario, where the three-dimensional tetrahedra in the zeolite framework are perfectly rigid and simply rotate relative to each other, then their 2D projected behavior in the (0 0 1) plane becomes equivalent to the idealized two-dimensional ‘rotating squares model’ with a Poisson’s ratio of ?1.     

X-ray diffraction study of a Nd3Ga5SiO14 crystal at 295 and 90 k and the structural basis for chirality

An accurate X-ray diffraction study of a Nd₃Ga₅SiO₁₄ crystal (sp. gr. P321, Z = 1) has been performed using repeated X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector at 295 and 90 K. The asymmetry of the disorder in the atomic positions in Nd₃Ga₅SiO₁₄ is described in two alternative ways: in terms of anharmonic atomic displacements (at 295 K R/wR = 0.80/0.92%; at 90 K R/wR = 0.82/0.76%) and using a split model (at 295 K R/wR = 0.85/0.97%; at 90 K R/wR = 0.80/0.74%). An analysis of the probability density function of finding an atom at a particular point in space shows that most of the atoms in the unit cell are asymmetrically or highly anisotropically disordered in the vicinity of their sites. Electron density regions for cations and anions that form pseudohelices were found. Such regions mimic a screw axis of symmetry and are responsible for the chirality of the structure.