Wyniki wyszukiwania - Biblioteka Nauki

1

Structural stability, elastic constants, bonding characteristics and thermal properties of zincblende, rocksalt and fluorite phases in copper nitrides: plane-wave pseudo-potential ab initio calculations

100%

Kanoun-Bouayed N. , Kanoun M. , Goumri-Said S.

Open Physics

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2011

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tom 9

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nr 1

205-212

EN

We report plane-wave pseudo-potential ab initio calculations using density functional theory in order to investigate the structural parameters, elastic constants, bonding properties and polycrystalline parameters of copper nitrides in zincblende, rocksalt and fluorite structures. Total and partial densities of states indicate a metallic character of these copper nitrides. We estimate bond strengths and types of atomic bonds using Mulliken charge density population analysis and by calculating the electronic localized function. These results reveal the coexistence of covalent, ionic, and metallic bonding.

2

Ab-initio study of structural, elastic, electronic and thermodynamic properties of BaxSr1-xS ternary alloys

100%

Chelli S. , Touam S. , Hamioud L. , Meradji H. , Ghemid S. , Hassan F. E.

Materials Science Poland

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2015

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tom Vol. 33, No. 4

879--886

EN

The structural, elastic, electronic and thermodynamic properties of BaxSr1-xS ternary alloys have been investigated using the full-potential (linearized) augmented plane wave method. The ground state properties, such as lattice constant, bulk modulus and elastic constants, are in good agreement with numerous experimental and theoretical data. The dependence of the lattice parameters, bulk modulus and band gap on the composition x was analyzed. Deviation of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence (LCD) was observed. The microscopic origins of the gap bowing were explained by using the approach of Zunger et al. The thermodynamic stability of BaxSr1-xS alloy was investigated by calculating the excess enthalpy of mixing, Delta H-m and the calculated phase diagram showed a broad miscibility gap with a critical temperature.

3

Influence of moisture content on elastic constants of Scots pine wood subjected to compression

100%

Güntekin E. , Akar S.

Drewno : prace naukowe, doniesienia, komunikaty

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2019

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tom vol. 62, nr 204

41--53

EN

Moisture content is the environmental factor that has the greatest influence on the physical and mechanical properties of wood materials. This research aimed to quantify the effect of moisture content on the elastic constants of Scots pine wood grown in Turkey under different humidity regimes. The elastic properties investigated include EL, ER, ET, GLR, GLT, GRT, ʋLR, ʋLT, ʋRL, ʋRT, ʋTL and ʋTR under compression. The compression strength in all principal directions was also studied. Specimens were cut from sapwood of pine logs and sorted into four matched MC groups. Clear wood samples were conditioned at 21°C and 45%, 65%, 85%, 95% RH, and subjected to compression tests. A biaxial extensometer was used to measure active and passive strain during loading. Young’s modulus, shear modulus, Poisson’s ratios and compression strength were calculated and compared for all orthotropic directions. The results indicate that the elastic and strength properties are significantly different in the principal directions. The Young’s modulus, shear modulus and compression strength of the tested samples were strongly affected by moisture content. These properties exhibit a linear decrease with increasing moisture content. Poisson’s ratios are not sensitive to MC changes.

4

Measurement of elastic constants of nematic liquid crystals with use of hybrid in-plane-switched cell

100%

Nowinowski-Kruszelnicki E. , Kędzierski J. , Raszewski Z. , Jaroszewicz L. , Kojdecki M. A. , Piecek W. , Perkowski P. , Olifierczuk M. , Miszczyk E. , Ogrosnik K. , Morawiak P.

Opto-Electronics Review

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2012

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tom Vol. 20, No. 3

255-259

EN

A new method for quick and pretty accurate measurements of splay, twist and bend elastic constants of nematic liquid crystals is experimentally verified. The main concept relies on exploiting only the electric field and determining magnitudes of nematic elastic constants from threshold fields for Freedericksz transitions in only one hybrid in-plane-switched cell. In such cell the deformations of an investigated liquid crystal are controlled by three separated pairs of electrodes confining measurement domains. In two of them inter-digital electrodes are mounted on one cell cover. Splay, twist and bend elastic constants can be measured by a proper choice of electrodes' configuration together with orienting cover coatings (without applying magnetic fields). In this paper, we describe layout of our cells and results of experimental tests by using different liquid crystals: 5CB and 6CHBT (with positive dielectric anisotropy), Demus' esters (with negative dielectric anisotropy) and new liquid crystals mixtures produced in our university.

5

A molecular dynamics study on iridium

100%

Ferah G. , Colakoglu K. , Ciftci Y. , Ozgen S. , Kazanc S.

Open Physics

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2007

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tom 5

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nr 2

207-220

EN

In this study, molecular dynamics simulations are performed by using a modified form of Morse potential function in the framework of the Embedded Atom Method (EAM). Temperature-and pressure-dependent behaviours of bulk modulus, second-order elastic constants (SOEC), and the linear-thermal expansion coefficient is calculated and compared with the available experimental data. The melting temperature is estimated from 3 different plots. The obtained results are in agreement with the available experimental findings for iridium.

6

Acoustical investigations of uranium chalcogenides

100%

Singh R. K. , Pandey K. K. , Singh M. P. , Singh R. P.

Materials Science Poland

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2009

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tom Vol. 27, No. 4/1

1041--1053

EN

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss was evaluated in uranium chalcogenides viz. UX, X= S, Se, Te in fcc phase in the temperature range 50-600 K for longitudinal and shear waves along the <100>, <110> and <111> directions of propagation. Electrostatic and Born-Mayer repulsive potentials were used to obtain second and third order elastic constants, taking the nearest neighbour distance and hardness parameter as the input data. Second and third order elastic constants (obtained at various temperatures) were used to obtain the Gruneisen parameters and non-linearity or anisotropy parameters, which in turn were used to evaluate the ultrasonic attenuation coefficient over the frequency square due to phonon-phonon interaction, (?/f 2)p-p in the Akhiezer regime. It has been found that at lower temperatures ?/f 2 increases rapidly with temperature, and at higher temperatures the rate of increase becomes small. Contribution to the total attenuation due to thermoelastic loss is negligible in comparison with that of phonon-phonon interaction, i.e. a major part of the energy from the sound wave is removed, due to interaction of acoustic phonons with thermal phonons (lattice vibrations).

7

Flexoelectric effect modelling

100%

Kapanowski A.

Opto-Electronics Review

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2008

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tom Vol. 16, No. 4

375-378

EN

A statistical theory of dipole flexoelectric (FE) polarization in liquid crystals is used to calculate temperature dependence of order parameters, elastic constants and FE coefficients. Two systems with polar wedge-shaped and banana-shaped molecules are investigated. In both cases, the FE coefficients are proportional to the dipole moment component parallel to the molecule symmetry axis. It results from the symmetries of interactions and of the Mayer function. The origin of the FE effect and microscopic pictures of the distorted phases are discussed.

8

Ultrasonic wave propagation in rare-earth monochalcogenides

100%

Singh D. , Pandey D. , Yadawa P.

Open Physics

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2009

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tom 7

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nr 1

198-205

EN

The ultrasonic attenuation in thulium monochalcogenides TmX (X=S, Se and Te) has been studied theoretically with a modified Mason’s approach in the temperature and range 100 K to 300 K along 〈100〉, 〈110〉〈111〉 crystallographic directions. The thulium monochalcogenides have attracted a lot of interest due to their complex physical and chemical characteristics. TmS, TmSe and TmTe are trivalent metal, mixed valence state, and divalent semiconductor, respectively. Coulomb and Born-Mayer potential is applied to evaluate the second- and third-order elastic constants. These elastic constants are used to compute ultrasonic parameters such as ultrasonic velocities, thermal relaxation time, and acoustic coupling constants that, in turn, are used to evaluate ultrasonic attenuation. A comparison of calculated ultrasonic parameters with available theoretical/experimental physical parameters gives information about classification of these materials.

9

Computations of the Acoustic-Waves Propagation-Parameters and the Subsequent Elastic Constants Derivation in a Single Layer on a Substrate

100%

Błachowicz T. , Beghi M.

Molecular and Quantum Acoustics

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2006

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tom Vol. 27

49-61

EN

The aim of this article is to present a phenomenon of acoustic waves propagation in a single layer on a semi-infinite substrate from the classical theory of elasticity point of view, and recall the description of this phenomenon by G. W. Farnell and E. L. Adler issued in 1972. Additionally, the purpose is to provide tutorial-type, step-by-step scheme for the numerical algorithm, using matrix formalism, in order to calculate frequencies, velocities and polarizations of different acoustic modes propagating within a layer. It was shown how from these calculations elastic constants of materials can be derived from fittings into dependencies between velocities and acoustic wave-vectors. The approach presented is related to Brillouin light scattering (BLS) experiments. The BLS experiments provide information about acoustic modes frequencies, velocities and wave-vectors, thus supporting the fitting procedure by reduction number of the unknown parameters.

10

Nanomechanical Properties of Metallic fcc Nanorods from Molecular Simulations with the Sutton-Chen Force Field

100%

Białoskorski M. , Rybicki J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2012

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tom Vol. 16, No 1-2

97-133

EN

Basic elastic constants (Young’s modulus, Poisson’s ratio, shear modulus) were determined for several monocrystalline, metallic (Ni, Cu, Pt, Au) nanorods using molecular dynamics with the Sutton-Chen force field. Stress-strain curves were also calculated and discussed.

11

Structural, Mechanical and Thermodynamic Properties Under Pressure Effect of Rubidium Telluride: First Principle Calculations

100%

Bidai K. , Ameri M. , Ameri I. , Bensaid D. , Slamani A. , Zaoui A. , Al-Douri Y.

Archives of Metallurgy and Materials

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2017

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tom Vol. 62, iss. 2A

865--871

EN

First-principles density functional theory calculations have been performed to investigate the structural, elastic and thermodynamic properties of rubidium telluride in cubic anti-fluorite (anti-CaF2-type) structure. The calculated ground-state properties of Rb2Te compound such as equilibrium lattice parameter and bulk moduli are investigated by generalized gradient approximation (GGA-PBE) that are based on the optimization of total energy. The elastic constants, Young’s and shear modulus, Poisson ratio, have also been calculated. Our results are in reasonable agreement with the available theoretical and experimental data. The pressure dependence of elastic constant and thermodynamic quantities under high pressure are also calculated and discussed.

12

Theoretical Calculations for Elastic and Thermodynamic Properties of NbN₂ under High Pressure

88%

Hou B.-S. , Liu K. , Mao X.-C. , Tan J. , Zhou X.-L.

Acta Physica Polonica A

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2017

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tom 132

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nr 4

1363-1370

EN

The structural and elastic properties of NbN₂ at high pressures were investigated through the first-principles calculation. Results indicate that NbN₂ is a potential hard material. NbN₂ meets mechanical stability criteria and possesses ductility within the pressure of 100 GPa. The elastic anisotropy under high pressure was achieved by the elastic anisotropy factors, which reduce with increasing pressure. Using the quasi-harmonic Debye model, we also investigated the thermodynamic properties of NbN₂.

13

Numerical homogenization of polymer/clay nanocomposites by the boundary element method

88%

Ptaszny J. , Fedeliński P.

Archives of Mechanics

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2011

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tom Vol. 63, nr 5-6

517-517

EN

The paper deals with the numerical homogenization of polymer/clay nanocomposites by using the boundary element method (BEM). The reinforcement has the form of stacks of parallel clay sheets modelled by effective isotropic particles. Two-dimensional representative volume elements (RVEs), containing randomly distributed parallel rectangular particles, are modelled and five plane-strain elastic constants of the orthotropic composite are analysed: two Young’s moduli, shear modulus and two Poisson’s ratios. The results are compared to experimental data, finite element method (FEM) results, and analytical models as well. The positive-definiteness and symmetry of the apparent compliance matrix are verified. All the comparisons and tests confirm validity of the applied method.

14

Elastic Constants by Resonant Ultrasound Spectroscopy – Application to Thermoelectrics and Aluminum Alloys

88%

Klobes B.

Scientific Journal of Gdynia Maritime University

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2019

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tom nr 112

60--68

EN

Resonant ultrasound spectroscopy is a non-destructive technique for determining the elastic constants of a material. In the context of thermoelectric materials, elastic constants can be used to investigate the speed of sound and, thus, the lattice thermal conductivity of a substance. For Mg2Si-Mg2Sn solid solutions, a possible connection between shear modulus and band convergence can be assumed in that way. Moreover, the rather low speed of sound in this system points towards a high contribution of optical phonons to thermal conductivity. Additionally, significant resonance frequency shifts are observed during natural aging of technical Al-Cu-Mg and Al-Mg-Si alloys, which are proposed to assist investigation of the early stages of clustering in the future.

15

Phase transition in CeSe, EuSe and LaSe under high pressure

88%

Singh S. , Singh R. , Gour A.

Open Physics

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2007

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tom 5

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nr 4

576-585

EN

The high pressure phase transition and elastic behavior of rare earth monoselenides (CeSe, EuSe and LaSe) which crystallize in a NaCl-structure have been investigated using the three body interaction potential (TBIP) approach. These interactions arise due to the electronshell deformation of the overlapping ions in crystals. The TBP model consists of a long range Coulomb, three body interactions and the short range overlap repulsive forces operative up to the second neighboring ions. The authors of this paper estimated the values of the phase transition pressure and the associated volume collapse to be closer than other calculations. Thus, the TBIP approach also promises to predict the phase transition pressure and pressure variations of elastic constants of lanthanide compounds.

16

Mechanic, Half-Metallic and Thermoelectric Properties of the PdZrTiAl under pressure: A DFT study

88%

Parsamehr S. , Boochani A. , Sartipi E. , Amiri M. , Solaymani S. , Naderi S. , Aminian A.

Archives of Metallurgy and Materials

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2020

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tom Vol. 65, iss. 1

459--470

EN

The half-metallic, mechanical, and transport properties of the quaternary Heusler compound of PdZrTiAl is discussed under hydrostatic pressures in the range of –11.4 GPa to 18.4 GPa in the framework of the density functional theory (DFT) and Boltzmann quasi-classical theory using the generalization gradient approximation (GGA). By applying the stress, the band gap in the minor spin increases so that the lowest band is obtained 0.25 eV at the pressure of –11.4 GPa while the maximum gap is calculated 0.9 eV at the pressure of 18.4 GPa. In all positive and negative pressures, the PdZrTiAl composition exhibits a half-metallic behavior 100% spin polarization at the Fermi level. It is also found that applying stress increases the Seebeck coefficient in both spin directions. In the minority spin, the n-type PdZrTiAl, the power factor (PF) for all the cases is greater in the equilibrium state than the strain and stress conditions whereas in the majority spin, the PF value of the stress state is greater than the other two. The non-dimensional figure of merit (ZT) is significant and is about one in spin down in the room temperature for the all pressure states that it remains on this value by applying pressure. The obtained elastic constants indicate that the PdZrTiAl crystalline structure has a mechanical stability. Based on the Yong (E), Bulk (B) and shear (G) modulus and Poisson (n) ratio, the brittle-ductile behavior of this compound has been investigated under pressure. The results indicate that PdZrTiAl has a ductile nature and it is a stiffness compound in which elastic and mechanical instability increases by applying strain.

17

Numerical investigation of influence of ionic space charge and flexoelectric polarization on measurements of elastic constants in nematic liquid crystals

88%

Buczkowska M. , Derfel G. , Konowalski M.

Opto-Electronics Review

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2009

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tom Vol. 17, No. 2

95-98

EN

Deformations of nematic layers caused by magnetic field allow determination of the elastic constants of liquid crystal. In this paper, we simulated numerically the deformations of planar and homeotropic nematic layers. The flexoelectric properties of the nematic and presence of ions were taken into account. Our aim was to show the influence of flexoelectricity on the results of the real measurement of the elastic constants k33 and k11. In these simulations, we calculated the optical phase difference Δ Φ between the ordinary and extraordinary rays of light passing through the layer placed between crossed polarizers as a function of the magnetic field induction B. One of the elastic constants can be calculated from the magnetic field threshold for deformation. The ratio k33/k11 can be found by means of fitting theoretical ΔΦ(B) dependence to the experimental results. The calculations reveal that the flexoelectric properties influence the deformations induced by the external magnetic field. In the case of highly pure samples, this may lead to false results of measurement of the elastic constants ratio k33/k11

18

Influence of size polydispersity on the elastic constants of F.C.C. crystals of static soft spheres

88%

Narojczyk J. W. , Wojciechowski K. W.

Materials Science Poland

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2008

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tom Vol. 26, No. 4

1001--1007

EN

Elastic constants of three-dimensional systems of soft spheres, interacting through n-inverse power potential and exhibiting aperiodicity (caused by the size polydispersity of the spheres), have been determined at 0 K by computer simulations. It has been shown that Poisson’s ratio, as well as other elastic constants, increase with increasing disorder in the system at a fixed number density of spheres.

19

Structure and Ultrasonic Properties of Vanadium Tellurite Glasses Containing Copper Oxide

88%

Abd El-Aal N. S. , Afifi H. A.

Archives of Acoustics

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2009

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tom Vol. 34, No. 4

641-654

EN

The elastic properties of vanadium tellurite glasses, 65TeO2-(35-x) V2O5-xCuO, with different compositions of Copper (x = 7.5 to 17.5 mol% in steps of 2.5 mol%) have been studied at room temperature (300 K). The ultrasonic velocity measurements have been made, using a transducer having resonating frequency of 4 MHz (both longitudinal and shear). The density, molar volume, and ultrasonic velocities show interesting features, which are used to explore the structural changes in the network. Elastic moduli, Poisson ratio, crosslink density, Microhardnes, and Debye temperature of the glasses have been determined using the experimental data. The composition dependence of the elastic properties explores useful information about the physical properties of the vanadium tellurite glasses doped with Copper. Quantitative analysis has been carried out in order to obtain more information about the structure of the glass under the study, based on bond compression model and the Makishima & Mackenzie model. The observed results through ultrasonic nondestructive evaluation, investigate the structural changes and mechanical properties of the glass.

20

Structural stability of TiO and TiN under high pressure

88%

Chauhan R. , Singh S. , Singh R.

Open Physics

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2008

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tom 6

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nr 2

277-282

EN

The high pressure phase transition and elastic behavior of Transition Metal Compounds (TiO and TiN) which crystallize in NaCl-structure have been investigated using the three body potential model (TBPM) approach. These interactions arise due to the electron-shell deformation of the overlapping ions in crystals. The TBP model consists of a long range Coulomb, three body interactions, and the short-range overlap repulsive forces operative up to the second neighboring ions. The authors of this paper estimated the values of the phase transition pressures, associated volume collapses, and elastic constants, all of which were found to be closer to available experimental data than other calculations. Thus, the TBPM approach promises to predict the phase transition pressure and pressure variations of elastic constants of Transition Metal compounds.