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1
Content available remote

Phase Transitions and Stability of Group IV BCC Metals

100%
Verma M., Verma A., Rathore R.
Acta Physica Polonica A
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1998
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vol. 93
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issue 3
479-489
EN
Born stability criteria were employed in the framework of extended generalised exponential potential to calculate the theoretical strength and range of stability of a perfect uniaxially stressed crystal lattice of group IV bcc metals: titanium, zirconium, and hafnium. The analysis depicts two ranges of stability, a bcc phase and a body centered tetragonal phase. The computed value of theoretical strength and strain of bcc Ti, Zr and Hf agree satisfactorily with the experimental limits. The second-order elastic constants C_{11} and C_{12} were also computed.
2
Content available remote

Effect of Nucleation on the Stability of BCC Metals

100%
Verma A., Verma M. L., Rathore R. P. S.
Acta Physica Polonica A
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1997
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vol. 91
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issue 3
583-596
EN
Numerical calculations are made of theoretical strength and range of stability of a perfect uniaxially stressed crystal lattice of bcc vanadium, niobium and tantalum in the framework of extended generalised exponential potential by applying Born stability criteria. Two ranges of stability, a bcc phase and a body centered tetragonal phase are found to exist. The computed values of theoretical strength and strain of bcc V, Nb and Ta agree reasonably well with the experimental limits.
3
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Elastic Constants of β-HgS

63%
Prieur J., Joffrin J., Szuszkiewicz W., Dynowska E., Górecka J., Witkowska B.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
487-491
EN
The elastic constants of single crystals of β-HgS highly doped with iron were directly determined at room temperature from the measurements of ultrasonic wave velocities by the pulse-echo technique. The values of c_{11}=6.750, c_{12}=5.186, and c_{44}=2.42 (given at 10^{10} N m^{-2} units) were obtained and compared with the experimental data taken for other mercury chalcogenides. The elastic characteristics of this group of materials is quite similar to those of Cd and Zn chalcogenides.
4
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Pressure Dependence of Elastic Constants in Zinc-Blende III-N and Their Influence on the Light Emission in Nitride Heterostructures

63%
Łepkowski S., Majewski J.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
559-566
EN
We studied the nonlinear elasticity effects for the case of III-N compounds. Particularly, we determined the pressure dependences of elastic constants, in zinc-blende InN, GaN, and AlN by performing ab initio calculations in the framework of plane-wave pseudopotential implementation of the density-functional theory. We found significant and almost linear increase in C_{11}, C_{12} with pressure for considered nitrides compounds. Much weaker dependence on pressure was observed for C_{44}. We also discussed pressure dependences of two-dimensional Poisson's ratio and elastic anisotropy coefficient. Finally, we showed that the pressure dependence of elastic constants results in significant reduction of the pressure coefficient of the energy emission in cubic InGaN/GaN quantum wells and essentially improves the agreement between experimental and theoretical values.
5
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Reinforcement of Elastic Polymer Matrix Filled with Ultrafine Particles

63%
Kryszewski M., Bąk G.
Acta Physica Polonica A
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1997
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vol. 92
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issue 6
1163-1167
EN
The nanofiller of noble metal may modify the properties of the polymer- noble metal composite even if the concentration of the metal nanoparticles is very low. The aim of this paper is to study the influence of colloidal particles in nanocomposites. For our studies we have selected polymethyl methacrylate-palladium nanocomposite. It is shown that the effective radius of the immobilised matrix environment is much greater than the radius of the palladium particles. Due to the binding of the matrix polymer and the palladium surface some volume of the surrounding matrix becomes immobilised giving rise to the effective increase in the size of the palladium filler. The analysis of a few models of nanocomposites used for interpretation of the mechanical properties has also been presented.
6
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Content available

Elastic Constants for Various Classes of Solids at High Temperature

63%
Liu Q., He Q.
Acta Physica Polonica A
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2007
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vol. 112
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issue 1
69-76
EN
In the present communication, a new relationship for the temperature dependences of elastic constants are developed using a new expression for the temperature dependence of bulk modulus and the formulation derived from Tallon's model. The proposed relationship is applied to study elastic constants of NaCl, KCl, CaF_2, MgO, CaO, and Mg_2SiO_4. The result obtained for second-order elastic constants are found to compare well with the experimental data.
7
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Ultrasonic Attenuation in Alloys

63%
Kor S., Singh R.
Acta Physica Polonica A
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1993
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vol. 83
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issue 6
751-758
EN
Ultrasonic attenuation was evaluated in metallic alloys, Ni_{x}Cu_{1-x} (x = 1.00, 0.70, 0.60, 0.45 and 0) due to phonon-phonon (p-p) interaction and thermoelastic loss in a wide temperature region along ⟨110⟩ crystallographic direction for longitudinal and shear waves. Ultrasonic Grüneisen parameters, nonlinearity constants and ultrasonic attenuation due to p-p interaction and thermoelastic loss were determined from 50 K to 500 K using the Born-Mayer and electrostatic potentials. The results were compared with available experimental results.
8
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Ultrasonic Attenuation in Dielectric Crystals

63%
Kor S., Singh R.
Acta Physica Polonica A
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1991
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vol. 80
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issue 6
805-810
EN
Ultrasonic attenuation and non-linearity parameters have been evaluated for dielectric crystals RbCl, RbBr and RbI in a wide temperature range. Basic physical parameters, nearest neighbour distance and hardness parameters of the substance and Coulomb and Born-Mayer potentials have been used to obtain ultrasonic attenuation due to phonon-viscosity mechanism along (100) direction of propagation for longitudinal and shear waves. Results are as expected and it has been concluded that ultrasonic attenuation is a fundamental property of the substance.
9
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Lattice Dynamics of Cubic Mercury Sulphide

63%
Szuszkiewicz W., Dybko K., Dynowska E., Górecka J., Witkowska B., Hennion B.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
947-950
EN
The acoustic phonon dispersion of mercury sulphide of zinc-blende structure (β-HgS) was studied by inelastic neutron scattering. The measurements were carried out at 19 K and 295 K on HgS crystals doped with Fe. A slight decrease in phonon frequencies with increasing temperature was found, the temperature dependence being the strongest for LA phonons with [ξ,ξ,0] propagation. From acoustic phonon dispersion the values of selected elastic constants were determined for β-HgS.
10
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Anharmonic Properties of Alkali Halides and Cyanides

63%
Kailash
Acta Physica Polonica A
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1996
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vol. 89
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issue 1
75-90
EN
Anharmonic properties of 16 alkali halides and 4 alkali cyanides are investigated using long-range Coulomb and short-range Born-Mayer potentials starting from the nearest-neighbour distance and repulsive parameter. This study includes the prediction of second, third and fourth order elastic constants, the pressure derivatives of second and third order elastic constants and partial contractions at elevated temperatures. The results obtained in present investigations are in reasonable agreement compared with experimental studies.
11
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Sound Attenuation at High Temperatures in Pt

63%
Singh R., Pandey K.
Acta Physica Polonica A
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2006
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vol. 109
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issue 2
219-228
EN
Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss was evaluated in VIII group transition metal Pt in a wide temperature range (100 K to 1500 K) for longitudinal and shear waves along〈100〉, 〈110〉 and〈111〉 directions and for shear waves polarised along different directions. Electrostatic and Born-Mayer potentials were used to obtain second and third order elastic constants, taking nearest-neighbour distance and hardness parameter as input data. Second and third order elastic constants data obtained at different temperatures were used to obtain Gruneisen parameters and non-linearity or anisotropy parameters which in turn were used to evaluate (α/f^2)_l and (α/f^2)_s in Akhiezer regime. The results were discussed and it was found that at lower temperatures (α/f^2) increases rapidly with temperature and then rate of increase becomes very small. Contribution to the total attenuation due to thermoelastic loss is negligible so that due to phonon-phonon interaction establishing that major part of energy from sound wave is removed due to interaction with thermal phonons (lattice vibrations).
12
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Elastic Behaviour and Lattice Vibrations in bcc V and Nb

63%
Verma A., Verma M., Rathore R.
|
EN
A model is developed by extending the generalised form of exponential potential known as extended generalised exponential potential to account for: (a) a realistic realization of interactions in all separations in general and that of small separations in particular, (b) three-body and electronic effects into the interaction in an alternative and simpler form, (c) a model free from usual fitting procedure. The model is employed to compute the cohesive energy, phonon spectra and second- and third-order elastic constants for group VA bcc metals V and Nb. The computed results showing good agreement with the experimental findings lend reliability and credibility to the potential.
13
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Orientation States in Rhombic NdGaO_{3}

63%
Savytskii D. I., Ubizskii S. B., Vasylechko L. O., Syvorotka I. M., Matkovskii A. O.
Acta Physica Polonica A
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1997
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vol. 92
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issue 1
231-236
EN
The ferroelastic domain structure of NdGaO_{3} is analyzed by three theories: group symmetry, tensor method and twinning by pseudosymmetry. The theories provide a coherent description of domain pairs and a determination of the position of W and S walls.
14
Publication available in full text mode
Content available

Nonlinear Elasticity in Wurtzite GaN/AlN Planar Superlattices and Quantum Dots

51%
Łepkowski S., Majewski J., Jurczak G.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
749-754
EN
The elastic stiffness tensors for wurtzite GaN and AlN show a significant hydrostatic pressure dependence, which is the evidence of nonlinear elasticity of these compounds. We have examined how pressure dependence of elastic constants for wurtzite nitrides influences elastic and piezoelectric properties of GaN/AlN planar superlattices and quantum dots. Particularly, we show that built-in hydrostatic pressure, present in both quantum wells of the GaN/AlN superlattices and GaN/AlN quantum dots, increases significantly by 0.3-0.7 GPa when nonlinear elasticity is used. Consequently, the compressive volumetric strain in quantum wells and quantum dots decreases in comparison to the case of the linear elastic theory. However, the z-component of the built-in electric field in the quantum wells and quantum dots increases considerably when nonlinear elasticity is taken into account. Both effects, i.e., a decrease in the compressive volumetric strain as well as an increase in the built-in electric field, decrease the band-to-band transition energies in the quantum wells and quantum dots.
15
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Ultrasonic Attenuation in Binary Alloys

51%
Kor S., Pandey G.
Acta Physica Polonica A
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1998
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vol. 93
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issue 3
491-497
EN
An attempt was made to study the ultrasonic attenuation in Cu-Zn, Ag-Cd, Ag-Mg and Ag-Zn alloys, due to phonon-phonon interaction at 300 K. The Morse potential was used to evaluate the second and third order elastic constants. How far the neighbouring atoms are effective and contributing to ultrasonic attenuation was studied. It is concluded that most of the ultrasonic attenuation is covered by the atoms from 1st to 8th shell. The contribution to ultrasonic attenuation due to 9th shell to 12th shell is very small. It is also concluded that alloys behave more or less in the same manner as metals.
16
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Effect of Nonlinear Elasticity on Interband and Intersubband Transition Energies in GaN/AlN Superlattices

51%
Łepkowski S.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
315-319
EN
We present a theoretical study of the effect of nonlinear elasticity on interband and intersubband transition energies in wurtzite GaN/AlN superlattices. The effect of nonlinear elasticity is considered by taking into account the changes of elastic constants caused by the intrinsic hydrostatic pressure, originating from lattice misfit between constituents of the superlattice. We show that the influence of the effect of the nonlinear elasticity on the interband and intersubband transition energies in the GaN/AlN superlattices depends crucially on the strain state of structures, in particular on the in-plane lattice constant of the buffer or the substrate. For the superlattices strained to AlGaN buffers with small aluminum concentrations, the effect of nonlinear elasticity increases significantly the interband transition energy and decreases the intersubband transition energy. For the superlattices strained to AlGaN buffers with large aluminum concentrations, the effect of nonlinear elasticity leads to a decrease in the interband transition energy and an increase in the intersubband transition energy.
17
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Theoretical Calculations of Cohesive and Electronic Properties of Quaternary AlGaInN Alloys

51%
Łopuszyński M., Bartoszek J., Majewski J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
449-454
EN
We present theoretical studies of the AlGaInN nitride quaternary alloys. The studies are based on ab initio calculations performed within the density functional theory and virtual crystal approximation. The equilibrium lattice constants, bulk moduli, and elastic constants were calculated for the whole possible range of concentrations of the alloy constituents. The theoretical values were then fitted with second- and third-order polynomials. For all properties studied, the considerable bowing was observed.
18
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Density Functional Studies of Nonlinear Elastic Properties for Zinc-Blende Nitrides

51%
Łopuszyński M., Majewski J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
443-447
EN
In this paper we present a method of calculating third-order elastic constants C_{ijk} and its application to zinc-blende nitrides AlN, GaN, and InN. Our approach is based on accurate ab initio calculations of both energy and stress as a function of applied strain. Ab initio computations are performed within density functional theory framework. To assess the reliability of the presented method, we compare our theoretical findings for GaAs with experimental results for C_{ijk} available for this material.
19
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Effect of Doping by Different Transition Metals on the Acoustical Properties of Alkali Borate Glasses

51%
Gaafar M., El-Batal F., El-Gazery M., Mansour S.
Acta Physica Polonica A
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2009
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vol. 115
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issue 3
671-678
EN
Longitudinal and shear ultrasonic wave velocities were measured in binary Li_2O-2B_2O_3 glasses doped with different transition metal oxides (TMOs) (where TMO = V_2O_5, Fe_2O_3, Cr_2O_3, NiO, TiO_2, MnO_2 and CuO) using pulse echo technique. Measurements were carried out at 4 MHz frequency and at room temperature. Elastic moduli and some other physical parameters such as acoustic impedance, Debye temperature, thermal expansion coefficient, and latent heat of melting were calculated. Results indicated that these parameters depend upon the TMO modifier i.e., the ionic radius of the transition metal cation. Quantitative analysis has been carried out, in order to obtain more information about the structure of these glasses, based on bond compression model, and the Makishima and Mackenzie model, i.e., the cation-anion bond of each TMO.
20
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Replica-Symmetry Broken Solution of Simple Pseudospin Model of Orientational Glass

51%
Walasek K., Lukierska-Walasek K., Wodawski M.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
407-410
EN
The first stage of the replica-symmetry breaking for a simple quadrupolar glass model using the Parisi ansatz has been performed in a wide range of temperatures including T = 0. It has been obtained that the entropy of the system increases considerably compared to that calculated within the replica symmetric theory.
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