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Wyświetlanie 1-14 z 14
Tytuł:
Elastic Behaviour and Lattice Vibrations in bcc V and Nb
Autorzy:
Verma, A.
Verma, M. L.
Rathore, R. P. S.
Powiązania:
https://bibliotekanauki.pl/articles/1946133.pdf
Data publikacji:
1996-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
63.20.Dj
62.20.Dc
Opis:
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.
Źródło:
Acta Physica Polonica A; 1996, 90, 3; 547-556
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Infrared Absorption in Single Crystals of (ET)$\text{}_{2}$C$\text{}_{60}$ Grown from CS$\text{}_{2}$ Solution
Autorzy:
Spitsina, N. G.
Semkin, V. N.
Graja, A.
Powiązania:
https://bibliotekanauki.pl/articles/1933393.pdf
Data publikacji:
1995-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
33.20.Ea
63.20.Dj
Opis:
Fourier transform IR absorption spectra of single crystals of the (ET)$\text{}_{2}$C$\text{}_{60}$ complex grown from the CS$\text{}_{2}$ solution as well as its components: C$\text{}_{60}$ and ET, also grown from CS$\text{}_{2}$ solution, are presented and discussed. It is shown that the rotation of C$\text{}_{60}$ is strongly hindered and ET molecules are bent in the crystal structure of the complex. The arguments for the domination of the van der Waals interactions are given.
Źródło:
Acta Physica Polonica A; 1995, 87, 4-5; 869-876
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Thermodynamics of Fcc Al Crystal from First Principles - Performance of Local Density and Generalized Gradient Approximations
Autorzy:
Scharoch, P.
Peisert, J.
Tatarczyk, K.
Powiązania:
https://bibliotekanauki.pl/articles/2047735.pdf
Data publikacji:
2007-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
65.40.-b
63.20.Dj
Opis:
Phonon dispersion relations in fcc Al crystal were calculated from first principles using density functional perturbation theory, as implemented in ABINIT code. The results are compared with experimental data as well as with the results of previously done ab initio calculations based on the direct method. A slightly better agreement of density functional perturbation theory phonons with experiment can be observed. The ab initio phonon energies were used to evaluate the partition function of the crystal, using the Monkhorst-Pack integration scheme. The quasiharmonic approximation was applied to relate the temperature dependent part of the free energy to volume. The lattice constant dependence of phonon energies was found to be almost linear, so the second order polynomial was considered as sufficient to approximate the dependence. A few examples of thermodynamic characteristics were evaluated: isobaric specific heat, linear thermal expansion coefficient, isothermal bulk modulus, and compared with the experimental data. The calculation was done both in the local density and the generalized gradient approximations for the exchange-correlation energy. The agreement with the experimental data appears to be very satisfactory, although better in the local density approximation than in the generalized gradient approximation.
Źródło:
Acta Physica Polonica A; 2007, 112, 3; 513-521
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin-Lattice Relaxation Beyond the Debye Approximation
Autorzy:
Witowski, A. M.
Bardyszewski, W.
Kutter, Ch.
Wyder, P.
Witkowska, B.
Mycielski, A.
Powiązania:
https://bibliotekanauki.pl/articles/1877052.pdf
Data publikacji:
1995-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.Fc
63.20.Dj
Opis:
In this paper we present the results of magnetization relaxation in HgCdMnTe at high magnetic fields. In this mixed crystal the TA phonons have an energy lower than the spin splitting of the Mn^{2+} ground orbital singlet at about 20 T, which allows to check the effect of phonons with wave vectors from the edges of the Brillouin zone on the spin-lattice relaxation.
Źródło:
Acta Physica Polonica A; 1995, 87, 2; 533-535
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Orientation Dependent Spin-Lattice Relaxation in CdMnSe
Autorzy:
Witowski, A. M.
Strutz, T.
Wyder, P.
Powiązania:
https://bibliotekanauki.pl/articles/1877057.pdf
Data publikacji:
1995-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.Fc
63.20.Dj
Opis:
The magnetization dynamics of Cd$\text{}_{1-x}$Mn$\text{}_{x}$Se at 4.5 K as a function of magnetic field up to 22 T was measured using a nonresonant technique. For x = 0.01 the relaxation does not depend on orientation and in higher fields the relaxation rates are proportional to B$\text{}^{3}$. For x = 0.02 a dependence on orientation is observed. The difference does not depend on magnetic field. This suggests that either the interaction between Mn ions responsible for spin-lattice relaxation in Mn clusters is anisotropic, or the relaxing clusters are oriented in a given manner with respect to the c axis.
Źródło:
Acta Physica Polonica A; 1995, 87, 2; 536-538
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On Phonon Dispersion in Alkali Metals
Autorzy:
Gajjar, P. N.
Thakore, B. Y.
Patel, H. K.
Jani, A. R.
Powiązania:
https://bibliotekanauki.pl/articles/1933617.pdf
Data publikacji:
1995-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.25.Cx
63.20.Dj
Opis:
In the present paper, the calculation of the phonon dispersion relations for alkali metals to second order in a local pseudopotential is discussed in terms of the real-space sum. Different forms of dielectric functions are employed to judge the varying effects of exchange and correlation on the phonon frequencies. The quantitative agreement of phonon frequencies for the alkali metals reflects, satisfactorily, the experimental trend.
Źródło:
Acta Physica Polonica A; 1995, 88, 3; 489-502
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Vibrational Modes in Si$\text{}_{x}$Ge$\text{}_{1-x}$ Alloys: Temperature and Compositional Dependence
Autorzy:
Lorenc, M.
Humlíček, J.
Powiązania:
https://bibliotekanauki.pl/articles/1968341.pdf
Data publikacji:
1997-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.30.Am
63.20.Dj
Opis:
We report infrared absorption spectra of crystalline Si$\text{}_{x}$Ge$\text{}_{1-x}$ alloys with silicon content 0 ≤ x ≤ 1 at room and liquid nitrogen temperature. We covered the spectral range from 375 to 1200 cm$\text{}^{-1}$ that includes the "Si-Ge" and "Si-Si" single-phonon transitions, the continuum of two-phonon processes, and the localized mode of interstitial oxygen. We study the change of vibrational structure and correlation between reference (pure Si and Ge) and alloy spectra. We observed shifts to lower wave numbers by about 1 cm$\text{}^{-1}$ of the two-phonon absorption bands per 1% increase in germanium concentration. Pronounced changes of the vibrational spectra upon lowering the temperature were detected.
Źródło:
Acta Physica Polonica A; 1997, 92, 5; 899-902
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Long-wavelength Optical Phonons in Cd$\text{}_{1-x}$Mn$\text{}_{x}$Se and Cd$\text{}_{1-x}$Fe$\text{}_{x}$Se Mixed Crystals
Autorzy:
Witowski, A. M.
Hausenblas, M.
Wyder, P.
Powiązania:
https://bibliotekanauki.pl/articles/1886654.pdf
Data publikacji:
1991-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
63.20.Dj
78.30.Fs
Opis:
The results of FIR reflectivity measurements for CdMnSe and CdFeSe are presented. These results are described theoretically using Dynamic Dielectric Function in which two phonon modes are included. The composition dependencies of mode parameters and dielectric constant are discussed.
Źródło:
Acta Physica Polonica A; 1991, 79, 2-3; 311-314
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Dispersion in Liquid Alkali Metals
Autorzy:
Gajjar, P. N.
Thakore, B. Y.
Jani, A. R.
Powiązania:
https://bibliotekanauki.pl/articles/1968966.pdf
Data publikacji:
1998-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.20.-p
61.25.Mv
63.20.Dj
Opis:
A local pseudopotential in the second-order perturbation theory is used to study the electron dispersion relation, the Fermi energy and deviation in the Fermi energy from free electron value for the liquid alkali metals. The influence of the five different forms of the local field correction functions on the aforesaid electronic properties is examined explicitly, which reflects the varying effects of screening. The depth of the first negative hump in the electron dispersion curves of the liquid alkali metals increases in the order Na, K, Rb, Cs.
Źródło:
Acta Physica Polonica A; 1998, 94, 1; 33-40
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Raman Spectroscopy of Cubic HgS:Fe
Autorzy:
Szuszkiewicz, W.
Witkowska, B.
Jouanne, M.
Powiązania:
https://bibliotekanauki.pl/articles/1873072.pdf
Data publikacji:
1995-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.50.Pp
63.20.Dj
78.30.Fs
Opis:
From the Raman spectra performed at temperatures from 10 K to 295 K for Hg$\text{}_{1-x}$Fe$\text{}_{x}$S crystals containing up to a few percent of iron the phonon energies for selected high-symmetry points of the Brillouin zone have been determined. A very high ionicity of these mixed crystals has been found. The TO phonon frequency value for β-HgS at Γ point, equal to about 177 cm$\text{}^{-1}$, suggested previously in the literature, has been confirmed.
Źródło:
Acta Physica Polonica A; 1995, 87, 2; 415-418
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The In$\text{}_{4}$Se$\text{}_{3}$ Crystal as a Three-Dimensional Imitative Model of Phenomena in One-Dimensional Crystals
Autorzy:
Bercha, D. M.
Sznajder, M.
Bercha, A. I.
Kharkhalis, L. Yu.
Rushchanskii, K.
Powiązania:
https://bibliotekanauki.pl/articles/1969018.pdf
Data publikacji:
1998-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.20.Nr
71.45.-d
63.20.Dj
63.20.Kr
63.22.+m
Opis:
For three-dimensional charge carriers described by the dispersion law with quartic terms of the wave vector, the density of states function similar as in the one-dimensional case was determined. This similarity allows the Pekar and Dejgen condenson states in the continuum approximation to exist. The calculated phonon spectrum reveals optical vibrations of a very low frequency, which favours the electron-phonon interaction and creation of the condenson states.
Źródło:
Acta Physica Polonica A; 1998, 94, 2; 250-254
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A Model Calculation of Infrared Spectra in Cyclohexanol
Autorzy:
Nowina Konopka, M.
Wasiutyński, T.
Powiązania:
https://bibliotekanauki.pl/articles/2011075.pdf
Data publikacji:
1999-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.50.Ah
63.20.Dj
78.20.Bh
78.30.Jw
78.30.Ly
Opis:
A model calculation based on semiempirical methods for the cyclohexanol molecules is presented. Energetically preferred molecular conformations and possibility of different hydrogen bond networks in the crystal are discussed. The calculated and the experimental infrared spectra are compared. The results corroborate earlier suggestions that the rich polymorphism of cyclohexanol is due to the existence of both axial and equatorial isomers in solid phases and different architecture of hydrogen bonds network.
Źródło:
Acta Physica Polonica A; 1999, 96, 3-4; 399-407
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Stress Induced Phononic Properties and Surface Waves in 2D Model of Auxetic Crystal
Autorzy:
Trzupek, D.
Twaróg, D.
Zieliński, P.
Powiązania:
https://bibliotekanauki.pl/articles/1809972.pdf
Data publikacji:
2009-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
63.20.D-
68.35.Ja
62.20.dj
Opis:
Elastic stiffness parameters are determined in a 2D model system of rigid rods interacting by harmonic force constants. Any positive ("normal" crystal) or negative (auxetic crystal) Poisson ratio can be obtained in this model as a function of the external stress. Conditions for opening an absolute stop band (phononic crystal) and for various kinds of surface waves are obtained.
Źródło:
Acta Physica Polonica A; 2009, 115, 2; 576-578
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Surface Dynamics and Phononic Properties of 2D Field Tunable Auxetic Crystal
Autorzy:
Twaróg, D.
Trzupek, D.
Zieliński, P.
Powiązania:
https://bibliotekanauki.pl/articles/1810018.pdf
Data publikacji:
2009-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
63.20.D-
68.35.Ja
62.20.dj
Opis:
The lattice in-plane dynamics is studied as a function of external field in a model of auxetic crystal consisting of rigid polar rods and of elastic springs. The phase speed of the transverse acoustic wave propagating parallel to the polar rods is shown to be higher than the speed of the longitudinal wave at strong fields. An absolute stop band for the lattice waves opens in the whole Brillouin zone with increasing field. The surface waves and resonances at a surface parallel to the rods are studied. Infinitely narrow resonances called exceptional surface waves are found within bulk bands at certain specific values of the parameters characterizing the surface. Generally, the surface layer should be significantly heavier and stiffer than the substrate for the phenomenon to occur.
Źródło:
Acta Physica Polonica A; 2009, 115, 2; 579-582
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-14 z 14

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