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The location of the liquidus in the low-pressure crystalline phase of SnI4 was determined utilizing in situ x-ray diffraction measurements under pressures up to approximately 3.5 GPa. The liquidus is not well fitted to a monotonically increasing curve such as Simon's equation, but breaks near 1.5 GPa and then becomes almost flat. The results are compared to those from molecular dynamics simulations. Ways to improve the model potential adopted in the simulations are discussed. [ABSTRACT FROM AUTHOR]

The effect of the differential speed rolling on the ridging resistance and the crystallographic texture evolution of ultra purified 17%Cr ferritic stainless steel was investigated in order to select the optimal procedure for improving the surface quality. In the present study, the three different cold rolling processes were carried out: a conventional cold rolling and two different speed ratios asymmetric rolling. In the conventional cold rolling, the ridging of ferritic stainless steel was pronounced due to the band-like clusters of grains with similar crystallographic orientations. For differential speed rolling, ridging depth decreased and ridging was less pronounced when a higher different speed ratio was applied. The results show that severe ridging is attributed to the presence of band-like clusters of γ-fiber (〈111〉//ND) oriented grains. The shear bands introduced by differential speed rolling can enhance the nucleation for recrystallization both in grain interiors and grain boundaries, which can fragment the band-like clusters of similar orientation effectively, promoting the random grain orientation and improving surface quality. [ABSTRACT FROM AUTHOR]

[Display omitted] The CSL/DSCL model for interfaces in crystalline materials offers a unified framework to study interface dislocations in phase boundaries and disconnections in grain boundaries. The model relies on the existence of a coincidence relation between the two lattices that meet at an interface. The model's ability to quantitatively predict the thermodynamics and kinetics of interfaces has been demonstrated for a limited set of symmetric tilt grain boundaries (STGBs) in cubic materials and twin boundaries. However, the lack of a general framework of interface defects prevents its applicability to arbitrary rational boundaries. In this paper, we present a mathematical framework based on the Smith normal form (SNF) for integer matrices to study the bicrystallography of rational phase and grain boundaries. One of the main results of the paper is a constructive proof of the invariance of the coincident site lattice (CSL) under discrete relative displacements of the parent lattices (of possibly different kind) by a displacement shift complete lattice (DSCL) vector. In addition, we obtain necessary and sufficient conditions on two lattices, related by not only rotations but also lattice distortions, for the existence of a coincidence relation. We first apply these results to explore coincidence relations in arbitrary phase boundaries, and study interface dislocations. In particular, we demonstrate the framework for a phase boundary formed by a strained hexagonal lattice and a square lattice. As a second application, we show how to enumerate all possible (geometric) disconnection modes in arbitrary rational grain boundaries, including glide and non-glide modes in both STGBs and asymmetric-tilt grain boundaries (ATGBs). The constructive nature of the framework lends itself to an algorithmic implementation based exclusively on integer matrix algebra to construct all interfaces that admit CSLs up to a prescribed size, and determine disconnection modes in grain boundaries. We demonstrate the use of SNF bicrystallography on selected bicrystal misorientation axes/angles in face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal (hex) lattices. [ABSTRACT FROM AUTHOR]

The article discusses a study which observed actuated conformational switching phenomenon taking place in a single crystal of a homodithiacalix[4]arene. The study introduced diatomic hetera bridges in the macrocyclic ring, in this case disulfide. The study explained that cooperative molecular motion is much more easily achieved for frameworks than in molecular crystals.

The kinetic peculiarities of diamond crystallization in multicomponent K-Na-Mg-Ca-carbonate-carbon system have been studied in conditions of diamond stability at 1500-1800°C and 7.5-8.5 GPa. It has been established that the diamond phase nucleation density at a fixed temperature of 1600°C decreases from 1.3 × 10 nuclei/mm at 8.5 GPa to 3.7 × 10 nuclei/mm at 7.5 GPa. The fluorescence spectra of obtained diamond crystals contain peaks at 504 nm ( H3-defect), 575 nm (NV-center), and 638 nm (NV-defect), caused by the presence of nitrogen impurity. In the cathodoluminescence spectra, an A-band with the maximum at 470 nm is present. The obtained data make it possible to assign the synthesized diamonds in the carbonate-carbon system to the mixed Ia + Ib type. [ABSTRACT FROM AUTHOR]

The discovery in 1900 by Gomberg that the trityl radical (Ph3C·) exists at room temperature is often considered to be the beginning of radical chemistry. Since then, persistent and even room-temperature stable radicals based on second-row and heavier elements have been synthesized. However, few of them have been characterized crystallographically, because they are either too reactive or dimerize in the solid state. Here, we show that a P2 fragment, capped with two bulky, strongly electron-releasing singlet carbenes (dicoordinate carbon compounds with only six valence electrons), can undergo one-electron oxidation, giving rise to room-temperature stable radical cations. Moreover, when N-heterocyclic carbenes are used, two-electron oxidation can also be performed, producing the corresponding stable dicationic diphosphene, which has to be regarded as a P22+ fragment coordinated by two carbenes. These results reveal a new application of stable singlet carbenes, the stabilization of paramagnetic species and electron-poor fragments. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the structural and spatial considerations in the N,N'-Diacyl- and Bis(alkoxycarbonyl)bispidinone series. It discourses on the structural distinctiveness and involution to other compounds of the bispidinone framework which believed to have been eluded notice. It offers details which considers the experiments and procedures where the given compound is further elaborated.

Interfaces are often believed to play a role in the mechanical behavior of mineralized biological and biomimetic materials. This motivates the micromechanical description of the elasticity and brittle failure of interfaces between crystals in a (dense) polycrystal, which serves as the skeleton of a porous material defined one observation scale above. Equilibrium and compatibility conditions, together with a suitable matrix-inclusion problem with a compliant interface, yield the homogenized elastic properties of the polycrystal, and of the porous material with polycrystalline solid phase. Incompressibility of single crystals guarantees finite shear stiffness of the polycrystal, even for vanishing interface stiffness, while increasing the latter generally leads to an increase of polycrystal shear stiffness. Corresponding elastic energy expressions give access to effective stresses representing the stress heterogeneities in the microstructures, which induce brittle failure. Thereby, Coulomb-type brittle failure of the crystalline interfaces implies Drucker–Prager-type (brittle, elastic limit-type) failure properties at the scale of the polycrystal. At the even higher scale of the porous material, high interfacial rigidities or low interfacial friction angles may result in closed elastic domains, indicating material failure even under hydrostatic pressure. This micromechanics model can satisfactorily reproduce the experimental strength data of different (brittle) hydroxyapatite biomaterials, across largely variable porosities. Thereby, the brittle failure criteria can be well approximated by micromechanically derived criteria referring to ductile solid matrices, both criteria being even identical if the solid matrix is incompressible. [ABSTRACT FROM AUTHOR]

Both the approach used and the progress made in the assignment of structure types to the crystal structures contained in the ICSD database are reported. Extending earlier work, an hierarchical set of criteria for the separation of isopointal structures into isoconfigurational structure types is used. It is shown how these criteria, which include the space group (number), Wyckoff sequence and Pearson symbol, c/ a ratio, β ranges, ANX formulae and, in certain cases, the necessary elements and forbidden elements, may be used to uniquely identify the representative structure types of the compounds contained in the ICSD database. [ABSTRACT FROM AUTHOR]

Proper solution of a macromolecular crystal structure based on anomalous scattering and/or isomorphous differences requires that the anomalous differences in reflection amplitudes be measured properly and that the correct enantiomer of the substructure be selected. If this information is wrong then the resulting electron-density maps will not show the correct structural features, but the reflection phases and map features will be related to the correct ones in a specific way. This text aims to explain how misinterpretation of the Bijvoet differences or of the substructure affects the resulting phases and electron-density maps. [ABSTRACT FROM AUTHOR]

[(n-C4H9)4N]2[Mo6O18(N-1-C10H6-2-CH3)] (1) has been prepared by the reaction of 1-amino-2-methylnaphthalene hydrochloride with [(n-C4H9)4N]4[α-Mo8O26] in the presence of 1,3-dicyclohexylcarbodiimide. Three solvent-free crystalline phases are isolated from the mixed solvents of acetone and acetic ether. The X-ray single-crystal structures of the three phases have been determined, showing the packing and supramolecular assembly characters (pseudohigher symmetry, helical chains, and π-π stacking) by which the effect of solvent polarity and crystallization speed on polymorphism in organic-inorganic hybrids has been demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The chemical potential of a curved interface contains a term that is proportional to the product of the interface curvature and the interface stiffness. In crystalline materials, the interface stiffness is a tensor. This paper examines several basic issues related to the properties of the interface stiffness, especially the determination of the interface stiffness in particular directions (i.e. the commonly used scalar form of the interface stiffness). Of the five parameters that describe an arbitrary grain boundary, only those describing the inclination are crucial for the scalar stiffness. We also examine the influence of crystal symmetry on the stiffness tensor for both free surfaces and grain boundaries. This results in substantial simplifications for cases in which interfaces possess mirror or rotational symmetries. An efficient method for determining the interface stiffness tensor using atomistic simulations is proposed. [Copyright &y& Elsevier]

We present an overview of friction processes expected between two ideal crystals of strong layers (graphite, MoS2, etc.) when one crystal is rotated with respect to the other by a certain angle θ. We assume perfect conditions: no impurities; no preexisting dislocations in the bulk of the crystals; slow gliding velocities. Two regimes show up: (a) Weak coupling when , where are typical intra- (inter-) layer interactions. Here we expect weak friction, controlled by two-phonon processes, and analyzed by Sokoloff et al. However, we point out that surface waves at the interface also play a role. (b) Strong coupling () where two orthogonal sets of screw disclinations should build up in the contact plane, as shown long ago by F.C. Frank. Here (to a first approximation) the dislocations are arranged in ladders, and we expect solid friction with a Peierls–Nabarro threshold stress. [ABSTRACT FROM AUTHOR]

We study decorated one-dimensional quasicrystals obtained by a non-standard projection of a part of two-dimensional lattice. We focus on the impact of varying relative positions of decorated sites. First we give a general expression for the structure factor. Subsequently we analyse an example of an extinction rule. [ABSTRACT FROM AUTHOR]

A model is proposed for metastable DX centers formed through Jahn–Teller distortion of the crystal lattice of cadmium telluride, i.e., through the displacement of a DCd residual donor impurity atom (where D is a Group III element of the periodic table) to the region of a nearest neighbor interstice. The configuration-coordinate diagram for a VCd–Di associated defect is constructed with due regard for the tetrahedral and hexagonal positions of interstitial atoms. The Stokes shift, n-type conductivity, location of the Fermi level, specific features of photoluminescence, and some other effects are explained in terms of the configuration-coordinate diagram. The results of experimental investigations of the energy spectrum of DX centers in cadmium telluride single crystals are in agreement with available theoretical data. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The parameters of hyperfine interactions in Pb3+F–8F–a tetragonal clusters of MeF2 crystals (Me = Ca, Sr, Ba) are interpreted. The contributions of the spin polarization to the parameters of the proper hyperfine interaction and additional (ligand) hyperfine interactions are calculated in the approximation of weak binding between a charge-compensating ion F–a and a cubic fragment in the tetragonal cluster. It is demonstrated that correct inclusion of the contributions from the spin polarization to the ligand isotropic hyperfine interaction for the F–a ion leads to anomalously large parameters of this interaction for MeF2 crystals. These results are in agreement with experimental data. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Shows that the interfacial profile between two bonded wafers can be directly determined using X-ray reflectivity without resorting to standard model-fitting of the data. Attempt to solve the phase problem inherent to any structure determination by scattering technique; Use of a known silicon/silicon oxide interface which acts as a phase reference for the reflected signals.

Explores the accuracy of crystal plate theories for high-frequency vibrations in the range of the fundamental thickness shear mode. Derivations of plate theories using various series expansions of the thickness modes; Accuracy of plate equations; Comparison of frequency spectra obtained using Mindlin's first-order plate theory and the three-dimensional equations of motion; Summary and conclusion.

The piezoelectric properties of [001]c poled 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3 single crystals were greatly enhanced by controlling their domain configurations. Contrary to the interpretation of charged domain walls being the main contributor to the piezoelectric enhancement, we found that smaller domain size and more neutral domain walls were the main contributors for the piezoelectric enhancement of these multidomain crystals. The properties of 109° neutral domain walls in 0.94Pb(Zn1/3Nb2/3)O3–0.06PbTiO3 single crystals were extracted by using a piezoelectric domain wall model. [ABSTRACT FROM AUTHOR]

In this work, we investigate the electronic and optical properties of self-assembled InN/GaN quantum dots. The one-particle states of the low-dimensional heterostructures are provided by a tight-binding model that fully includes the wurtzite crystal structure on an atomistic level. Optical dipole and Coulomb matrix elements are calculated from these one-particle wave functions and serve as an input for full configuration interaction calculations. We present multiexciton emission spectra and discuss in detail how Coulomb correlations and oscillator strengths are changed by the piezoelectric fields present in the structure. Vanishing exciton and biexciton ground state emission for small lens-shaped dots is predicted. [ABSTRACT FROM AUTHOR]

The band structure of the TlGaTe2 compound is calculated by the pseudopotential method. The spectral dependences of the real and imaginary parts of the complex permittivity are determined in the case when the polarizations are parallel and perpendicular to the optic axis of the crystal. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Models consisting of chains of particles that are coupled to their neighbours appear in many applications in physics or engineering, such as in the study of dynamics of mono-atomic and multi-atomic lattices, the resonances of crystals with impurities and the response of damaged bladed discs. Analytical properties of the dynamic responses of such disturbed chains of identical springs and masses are presented, including when damping is present. Several remarkable properties in the location of the resonances (poles) and anti-resonances (zeros) of the displacements in the frequency domain are presented and proved. In particular, it is shown that there exists an elliptical region in the frequency-disturbance magnitude plane from which zeros are excluded and the discrete values of the frequency and disturbance at which double poles occur are identified. A particular focus is on a local disturbance, such as when a spring or damper is modified at or between the first and last masses. It is demonstrated how, notably through normalization, the techniques and results of the paper apply to a broad category of more complex systems in physics, chemistry and engineering. [ABSTRACT FROM AUTHOR]

In the mol­ecule of the title compound, C28H23N3O2, the nitro group is almost perpendicular to the carbazole ring to which it is attached. The crystal packing is determined by C—H⋯O and π–π inter­actions, where the nitrated carbazole ring of one mol­ecule associates in a shifted parallel planar orientation with the centrosymmetrically related non-nitrated carbazole ring of a neighbouring mol­ecule. [ABSTRACT FROM AUTHOR]

Assesses the EP program for determining crystallite orientations. Evaluation of the crystallographic problem; Description of the software and hardware environments; Specifications of the program.