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Atomic Displacements (atomic + displacement)
Terms modified by Atomic Displacements Selected AbstractsSymmetry Analysis of Antiferroquadrupolar Order and Accompanying Atomic Displacements in CeB6.CHEMINFORM, Issue 37 2005Wieslawa Sikora Abstract For Abstract see ChemInform Abstract in Full Text. [source] H-doped PbTiO3: Structure and electronic propertiesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2007Arvids Stashans Abstract The geometry and electronic properties of the interstitial H atom in the tetragonal PbTiO3 crystal have been studied using an advanced quantum chemical computer code developed for the modeling of crystals. The inserted H atom was found to bind to one of the O atoms and to form the hydroxyl, OH group, with the inter-atomic distance equal to 0.93 Å and 1.00 Å for the hydroxyls containing O atom in the dimerized and nondimerized TiOTi chains, respectively. Atomic displacements in the vicinity of OH complex are calculated and analyzed in relation to the H-produced changes upon the atomic charges in defective region. The role of H impurity on the ferroelectric polarization in the tetragonal PbTiO3 is discussed in terms of the results obtained in our research and those presented in the other studies on this subject. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Atomic displacements at and order of all phase transitions in multiferroic YMnO3 and BaTiO3ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009S. C. Abrahams Coordinate analysis of the multiple phase transitions in hexagonal YMnO3 leads to the prediction of a previously unknown aristotype phase, with the resulting phase-transition sequence: P63,cm,(e.g.) ,P63cm,P63/mcm,P63/mmc,P6/mmm. Below the Néel temperature TN, 75,K, the structure is antiferromagnetic with the magnetic symmetry not yet determined. Above TN the P63cm phase is ferroelectric with Curie temperature TC, 1105,K. The nonpolar paramagnetic phase stable between TC and ,,1360,K transforms to a second nonpolar paramagnetic phase stable to ,,1600,K, with unit-cell volume one-third that below 1360,K. The predicted aristotype phase at the highest temperature is nonpolar and paramagnetic, with unit-cell volume reduced by a further factor of 2. Coordinate analysis of the three well known phase transitions undergone by tetragonal BaTiO3, with space-group sequence R3m,Amm2 ,P4mm,Pmm, provides a basis for deriving the aristotype phase in YMnO3. Landau theory allows the I , II, III , IV and IV , V phase transitions in YMnO3, and also the I , II phase transition in BaTiO3, to be continuous; all four, however, unambiguously exhibit first-order characteristics. The origin of phase transitions, permitted by theory to be second order, that are first order instead have not yet been thoroughly investigated; several possibilities are briefly considered. [source] Bridging domain methods for coupled atomistic,continuum models with L2 or H1 couplingsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2009P.-A. Guidault Abstract A bridging domain method for coupled atomistic,continuum models is proposed that enables to compare various coupling terms. The approach does not require the finite element mesh to match the lattice spacing of the atomic model. It is based on an overlapping domain decomposition method that makes use of Lagrange multipliers and weight functions in the coupling zone in order to distribute the energy between the two competing models. Two couplings are investigated. The L2 coupling enforces the continuity of displacements between the two models directly. The H1 coupling involves the definition of a strain measure. For this purpose, a moving least-square interpolant of the atomic displacement is defined. The choice of the weight functions is studied. Patch tests and a graphene sheet with a crack are studied. It is shown that both continuous and discontinuous weight functions can be used with the H1 coupling whereas the L2 coupling requires continuous weight functions. For the examples developed herein, the L2 coupling produces less error in the zone of interest. The flexibility of the H1 coupling with constant weight function may be beneficial but the results may be affected depending on the topology of the bridging zone. Copyright © 2008 John Wiley & Sons, Ltd. [source] Structure,property correlation over five phases and four transitions in Pb5Al3F19ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2003S. C. Abrahams The calorimetric and dielectric properties of Pb5Al3F19 in the five phases stable under ambient pressure are correlated with structure for fuller characterization of each phase. The first-order transition between ferroelectric phase V and antiferroelectric phase IV at TV,IV = 260,(5),K exhibits a thermal hysteresis of 135,(5),K on heating, with a maximum atomic displacement ,(xyz)max = 1.21,(6),Å; the transition from phase IV to ferroelastic phase III at 315,(5),K is also first order but with a thermal hysteresis of 10,(5),K and ,(xyz)max = 0.92,(7) ,Å; that from phase III to paraelastic phase II at 360,(5),K is second order without hysteresis and has ,(xyz)max = 0.69,(4),Å; and the transition from phase II to paraelectric phase I at 670,(5),K is second or higher order, with ,(xyz)max = 0.7,(4),Å. The measured entropy change ,S at TV,IV agrees well with ,S as derived from the increased configurational energy by Stirling's approximation. For all other phase transitions, 0.5 ,,S > 0,J,mol,1,K,1 is consistent with an entropy change caused primarily by the changes in the vibrational energy. The structure of phase III is determined both by group theoretical/normal mode analysis and by consideration of the structures of phases II, IV and V reported previously; refinement is by simultaneous Rietveld analysis of the X-ray and neutron diffraction powder profiles. The structure of prototypic phase I is predicted on the basis of the atomic arrangement in phases II, III, IV and V. The introduction of 3d electrons into the Pb5Al3F19 lattice disturbs the structural equilibrium, the addition of 0.04% Cr3+ causing significant changes in atomic positions and increasing TIV,III by ,15,K. Substitution of Al3+ by 20% or more Cr3+ eliminates the potential minima that otherwise stabilize phases IV, III and II. [source] DFT Study of Effects of Potassium Doping on Band Structure of Crystalline Cuprous AzideCHINESE JOURNAL OF CHEMISTRY, Issue 12 2008Wei-Hua ZHU Abstract The structure and defect formation energies of the K-doped CuN3 were studied using density functional theory within the generalized gradient approximation. The results show that the K-doping breaks the azide symmetry and causes asymmetric atomic displacement. As the K-doping level increases, the band gap of the doped system gradually increases. The K impurity is easily incorporated into the crystal thermodynamically. The Cu vacancy is easily created thermodynamically and the K impurity can serve as nucleation centers for vacancy clustering. Finally the effects of K-doping concentrations on the sensitivity of CuN3 were understood based on electronic structures. [source] Polarization switching in BaTiO3 thin films measured by X-ray diffraction exploiting anomalous dispersionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2004S. J. Van Reeuwijk Films of BaTiO3 ranging from 20,nm to 300,nm in thickness were grown with pulsed laser deposition on Nb:SrTiO3. The quality of the layers was investigated using atomic force microscopy, X-ray reflectivity and X-ray diffraction. Both the micrographs and the X-ray reflectivity spectra indicate a smooth surface of the layers. The X-ray diffraction profiles measured using synchrotron radiation show features characteristic for highly crystalline thin films. The application of an external electric field parallel to the c axis changes an hkl reflection of BaTiO3 to an hk reflection. Due to the anomalous dispersion, the intensities of these two reflections are not equal and the atomic displacements can be determined from the intensity differences. The electric field-induced intensity changes can be as large as a few percent, which makes data collection from a 100,nm film using Cu K, radiation from an X-ray tube feasible. The ,I/I values of a number of reflections from the 20 and 50,nm films were measured using synchrotron radiation. The observed ,I/I values were in good agreement with the intensity changes expected for polarization switching in the bulk. [source] Silver nanocluster containing diamond like carbonPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2008F. Schwarz Abstract Applying Diamond Like Carbon (DLC) as medical coating has become well established since large scale plasma processes like Plasma Immersion Ion Implantation and Deposition (PIII&D) are available. Now the focus of research lies on systematic modification of certain biological relevant properties and the most recent field of interest turned to generating antimicrobial behaviour. This is desirable for medical tools as well as for different types of medical implants. Since silver and copper are known to provide a bactericidal effect, one tries to introduce clusters of these noble metals into the carbon matrix. The basic principle of the method presented is to convert a metal containing polymer film into DLC by ion bombardment. In this paper the hydrogenated DLC matrix is characterized and the evolution of the metal particles is studied. By means of film composition (RBS/ERD), bonding structure (Raman spectroscopy) and hardness (nanoindentation), the dependency of these material properties on ion species, energy and fluence is investigated. TEM imaging is used to visualize the film structure. Upon ion irradiation of the polymer films, increased density and considerable loss of hydrogen can be observed, which both are controlled by ion fluence and mass. The crosslinking of the carbon network, caused by hydrogen drive out as well as atomic displacements in collision cascades, results in the formation of a-C:H. The silver particles in the film some ion induced growth, but still remain as nanoclusters in the a-C:H matrix. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] First-principles modelling of defects in advanced nuclear fuelsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007E. A. Kotomin Abstract In this paper we present and discuss the results of first first-principle modelling of point defects in nitride nuclear fuels. Calculations have been performed using the VASP computer code combined with supercells containing up to 250 atoms. The effective atomic charges, the electronic density redistribution, atomic displacements around U and N vacancies and their formation energies are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dynamics of molecules in crystals from multi-temperature anisotropic displacement parameters.ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2000A new model for analysing the temperature evolution of anisotropic displacement parameters (ADP's) is presented. It allows for a separation of temperature-dependent from temperature-independent contributions to ADP's and provides a fairly detailed description of the temperature-dependent large-amplitude molecular motions in crystals in terms of correlated atomic displacements and associated effective vibrational frequencies. It can detect disorder in the crystal structure, systematic error in the diffraction data and the effects of non-spherical electron-density distributions on ADP's in X-ray data. The analysis requires diffraction data measured at multiple temperatures. [source] Dynamics of molecules in crystals from multi-temperature anisotropic displacement parameters.ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2000The temperature evolution of atomic anisotropic displacement parameters (ADP's) of perdeuterobenzene and of urea in the temperature range between 12 and 123,K is investigated in terms of the model presented in paper I. For the benzene molecule, the temperature-dependent contributions to the ADP's are well described by three molecular librations and three molecular translations. For the urea molecule, the analysis revealed a low-frequency high-amplitude normal mode (~64,cm,1), which combines out-of-plane deformations of the NH2 groups with molecular libration. The pyramidalization motion allows the hydrogen-bonding pattern to be retained quite well, whereas this pattern is heavily distorted in the higher-frequency molecular librations. The results presented for urea go a step beyond those obtainable in a conventional rigid-body or segmented-rigid-body analysis because they show how correlations of atomic displacements in molecular crystals can be determined from the temperature evolution of ADP's. For both molecules, the analysis reveals temperature-independent contributions to the ADP's accounting for the high-frequency internal vibrations. It is the first time that such contributions have been extracted directly from single-crystal diffraction data for light atoms like hydrogen and deuterium as well as for heavier atoms like carbon, nitrogen and oxygen. These contributions agree well with those calculated from independent spectroscopic information. [source] Keratin mutations in patients with epidermolysis bullosa simplex: correlations between phenotype severity and disturbance of intermediate filament molecular structureBRITISH JOURNAL OF DERMATOLOGY, Issue 5 2010B. Je, ábková Summary Background, Epidermolysis bullosa simplex (EBS) is an inherited skin disorder caused by mutations in the keratin 5 (KRT5) and keratin 14 (KRT14) genes, with fragility of basal keratinocytes leading to epidermal cytolysis and blistering. Objectives, In this study, we characterized mutations in KRT5 and KRT14 genes in patients with EBS and investigated their possible structure,function correlations. Materials and methods, Mutations were characterized using polymerase chain reaction (PCR) and DNA sequencing. Further, to explore possible correlations with function, the structural effects of the mutations in segment 2B of KRT5 and KRT14 and associated with EBS in our patients, as well as those reported previously, were modelled by molecular dynamics with the aid of the known crystal structure of the analogous segment of human vimentin. Results, We have identified mutations in the KRT5 and KRT14 genes in 16 of 23 families affected by EBS in the Czech Republic. Eleven different sequence variants were found, of which four have not been reported previously. Novel mutations were found in two patients with the EBS-Dowling,Meara variant (EBS-DM) [KRT14-p.Ser128Pro and KRT14-p.Gln374_Leu387dup(14)] and in three patients with localized EBS (KRT14-p.Leu136Pro and KRT5-p.Val143Ala). Molecular dynamics studies show that the mutations p.Glu411del and p.Ile467Thr perturb the secondary alpha-helical structure of the mutated polypeptide chain, the deletion p.Glu411del in KRT14 has a strong but only local influence on the secondary structure of KRT14, and the structural impact of the mutation p.Ile467Thr in KRT5 is spread along the helix to the C-terminus. In all the other point mutations studied, the direct structural impact was significantly weaker and did not destroy the alpha-helical pattern of the secondary protein structure. The changes of 3-D structure of the KRT5/KRT14 dimer induced by the steric structural impact of the single point mutations, and the resulting altered inter- and intramolecular contacts, are spread along the protein helices to the protein C-terminus, but the overall alpha-helical character of the secondary structure is not destroyed and the atomic displacements induced by mutations cause only limited-scale changes of the quaternary structure of the dimer. Conclusions, The results of molecular modelling show relationships between patients' phenotypes and the structural effects of individual mutations. [source] |