共查询到20条相似文献,搜索用时 703 毫秒
1.
M. Ricker J. Bachteler H.-R. Trebin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):351-363
In quasicrystals, there are not only conventional, but also phason displacement fields and associated Burgers vectors. We
have calculated approximate solutions for the elastic fields induced by two-, three- and fivefold straight screw- and edge-dislocations
in infinite icosahedral quasicrystals by means of a generalized perturbation method. Starting from the solution for elastic
isotropy in phonon and phason spaces, corrections of higher order reflect the two-, three- and fivefold symmetry of the elastic
fields surrounding screw dislocations. The fields of special edge dislocations display characteristic symmetries also, which
can be seen from the contributions of all orders.
Received 21 February 2001 and Received in final form 27 June 2001 相似文献
2.
In diffraction from some icosahedral quasicrystals, diffuse scattering is concentrated on arcs in TEM diffraction patterns. The new Ti-Mn icosahedral phase produces much more intense arcs than previously observed in quasicrystals, allowing a significantly deeper study of them. 相似文献
3.
P.T. Jochym K. Parlinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):265-268
Ab initio calculations and a direct method are applied to derive the phonon dispersion relations and phonon density of states for the
ZrC crystal. The results are in good agreement with neutron scattering data. The force constants are determined from the Hellmann-Feynman
forces induced by atomic displacements in a 222 supercell. The elastic constants are found using the deformation method and successfully compare with experimental data.
Received 2 July 1999 and Received in final form 26 November 1999 相似文献
4.
R. Lefort B. Toudic J. Etrillard F. Guillaume P. Bourges R. Currat T. Breczewski 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):51-57
The diffraction pattern of n-alkane/urea inclusion compounds is known to contain a broad diffuse scattering related to the
molecular form factor of the alkane species, indicating individual rotational and/or translational disorder of these molecules.
Inelastic coherent neutron scattering reveals for the first time the entirely dynamical character of the alkane molecular
disorder around room temperature. This observation fully agrees with a recent model of the coherent scattering cross section
of totally uncorrelated motions. In the ordered phase this diffuse scattering remains, but elastic, and very low energy molecular
vibrational modes are evidenced. These observations are discussed in relation with previous incoherent neutron scattering
results.
Received 9 February 2001 and Received in final form 1st August 2001 相似文献
5.
J. Bachteler H.-R. Trebin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):299-306
The elastic theory of quasicrystals considers, in addition to the “normal” displacement field, three “phason” degrees of freedom.
We present an approximative solution for the elastic Green's function of icosahedral quasicrystals, assuming that the coupling
between the phonons and phasons is small.
Received: 18 December 1997 / Accepted: 6 March 1998 相似文献
6.
Very sharp Bragg reflections accompanied by diffuse scattering phenomena are typical for most stable quasicrystals. The correlation length of the quasiperiodic average structure can reach several micrometers as proved by high-resolution X-ray diffraction experiments. This corresponds to a structural perfection of some quasicrystals similar to that of silicon. Nevertheless, the omnipresent diffuse scattering indicates significant deviations from a strictly ordered quasiperiodic structure especially in the case of decagonal phases. These structural deviations may be caused by phason fluctuations, by disorder in the packing of the basic atomic clusters, by the formation of nanodomains, by chemical disorder, or by superstructure formation on a short-range scale. Characteristic examples of different types of structural disorder present in icosahedral and decagonal quasicrystals are reported. The diffuse scattering phenomena in decagonal Al-Co-Ni as a function of composition and temperature are discussed in more detail. 相似文献
7.
M. Belhadi O. Rafil R. Tigrine A. Khater J. Hardy A. Virlouvet K. Maschke 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):435-443
The influence of linear defect boundaries on the transmission and scattering of elastic waves in quasi-two-dimensional wave-guides
is studied using the matching method. A linear defect boundary separating two wave-guide crystalline lattice domains is characterised
here by a linear chain of defect masses and by modified elastic constants in the boundary, different from their values in
the bulk of the domains. In particular a square lattice is considered to model the domains of the two-dimensional planar wave-guide
containing the linear defect. The reflection and transmission probabilities, and the total transmission probabilities are
calculated numerically and presented for the scattering processes in a variety of cases. We show that the interaction between
the localised modes introduced by the defect boundary and the propagating modes of the system leads to Fano resonances. These
resonances shift to higher (lower) frequencies for smaller (larger) defect masses, and for the same mass as function of the
angle of the incident wave. Other spectral features shown to exist are due to interference effects especially at oblique incidence
and when modifying the boundary elastic constants.
Received 8 November 1999 and Received in final form 14 January 2000 相似文献
8.
Lyotropic bicontinuous cubic phase single crystals investigated using high-resolved X-ray scattering
Single crystals of an Ia
d bicontinuous direct cubic phase formed by a non-ionic surfactant in water are investigated using high-resolved X-ray diffraction.
The shape of the Bragg peaks confirms the existence of a 3D long-range order inside the cubic phase. A weak diffuse scattered
intensity signal is measured very near the Bragg peaks. We attribute this signal to thermal diffuse scattering (TDS) and we
give an estimation of the contribution of elastic waves to this TDS.
Received 4 May 2000 相似文献
9.
P.T. Jochym K. Parlinski M. Sternik 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):9-13
Ab initio calculations and a direct method have been applied to derive the phonon dispersion curves and phonon density of states for
the TiC crystal. The results are compared and found to be in a good agreement with the experimental neutron scattering data.
The force constants have been determined from the Hellmann-Feynman forces induced by atomic displacements in a supercell. The calculated phonon density of states suggests that vibrations of Ti atoms form acoustic branches, whereas the
motion of C atoms is confined to optic branches. The elastic constants have been found using the deformation method and compared
with the results obtained from acoustic phonon slopes.
Received 23 February 1998 相似文献
10.
Fundamental and experimental differences between X-ray and neutron scattering methods are outlined and the advantages of either radiation for the study of disorder in crystals are described. Special emphasis is laid on their complementarity, e.g. to identify the atomic species involved in the disorder or to decide between the elastic or inelastic nature of the diffuse scattering (static or dynamic disorder). This is illustrated by three examples: LiNbO3 (dynamic nature of chain-like disorder), doped Zr02 (identification of cationic and anionic disorder components) and decagonal quasicrystals (distinction between quasi-isoelectronic elements). 相似文献
11.
12.
M. Kaisermayr B. Sepiol H. Thiess G. Vogl E.E. Alp W. Sturhahn 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):335-341
Time-domain interferometry of synchrotron radiation (TDI) has recently been used as a tool for investigating diffusion in
glasses. This work deals with an extension of this technique to ordered structures. In a TDI experiment performed on the B2 alloy CoGa at the APS the intensity scattered into Bragg directions showed no detectable quasielastic signal. Experimental
lower limits of the elastic contribution are given. They are in accordance with the coherent scattering function derived in
this paper. This result indicates that TDI can be applied to diffusion in crystalline solids, e.g. intermetallic alloys, by using diffuse scattering. Requirements and limitations of diffuse scattering experiments are discussed.
Received 21 September 2000 and Received in final form 13 December 2000 相似文献
13.
P. Gong C.-Z. Hu X. Zhou L. Miao X. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):477-481
Since quasicrystals have positional and orientational
long-range order, they are essentially anisotropic. However, the
researches show that some physical properties of quasicrystals are
isotropic. On the other hand, quasicrystals have additional phason
degrees of freedom which can influence on their physical behaviours.
To reveal the quasicrystal anisotropy, we investigate the
quasicrystal elasticity and other physical properties, such as
thermal expansion, piezoelectric and piezoresistance, for which one
must consider the contributions of the phason field. The results indicate that:
for the elastic properties, within linear phonon domain all
quasicrystals are isotropic, and within nonlinear phonon domain the
planar quasicrystals are still isotropic but the icosahedral
quasicrystals are anisotropic. Moreover, the nonlinear elastic
properties due to the coupling between phonons and phasons may
reveal the anisotropic structure of QCs. For the other physical
properties all quasicrystals behave like isotropic media except for
piezoresistance properties of icosahedral
quasicrystals due to the phason field. 相似文献
14.
Y.Z. Peng T.Y. Fan 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):39-44
In this paper we develop a general method to solve elastic three-dimensional problems for one-dimensional hexagonal quasicrystals
with point groups 6mm, 62h2h,
m2h and 6/mmm, including crack and indentation problems. Exact solutions are obtained by using Fourier series and Hankel transform
methods. These results automatically reduce to those in the classical elasticity theory when the phason field is absent.
Received 6 October 2000 相似文献
15.
S. Residori N. Olivi-Tran E. Pampaloni 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):15-20
In the case of 2D optical patterns, frustration comes from the interplay between the physical constraints (light-matter interaction)
and the geometrical constraints (cavity length and structure). Depending on the dynamical parameters, we are able to single
out two distinct behaviors. For small diffusion and close to threshold, the system is forced to fulfill the geometrical constraints
giving rise to a phase dynamics of quasicrystals. For larger diffusion, the system fragmentates into spatial domains giving
rise to a competition between different patterns. By means of a geometrical argument, we show that the spatial distribution
of domains is related to the symmetry imposed by the geometrical constraint and that the domain borders are disinclination
defects. These defects being the nucleation centers of spatial domains, they trigger the onset of pattern competition.
Received 27 December 1999 and Received in final form 29 March 2000 相似文献
16.
17.
We report on the absolute scale measurement of the x-ray diffuse scattering in the ZnMgSc icosahedral quasicrystal and its periodic approximant. Whereas the diffuse scattering in the approximant is purely accounted for by thermal diffuse scattering, an additional signal is observed in the quasicrystal. It is related to phason fluctuations as indicated by its Q(2)(per) dependence. Moreover, when compared to previous measurements carried out on the i-AlPdMn phase, we find that the amount of diffuse scattering is smaller in the i-ZnMgSc phase, in agreement with larger phason elastic constants in this phase. This is confirmed by the observation of a large number of weak Bragg peaks having a high Q(per) reciprocal space component. 相似文献
18.
TU Mei & HUANG Yaoxiong Institute of Biomedical Engineering Jinan University Guangzhou China Correspondence should be addressed to Huang Yaoxiong 《中国科学G辑(英文版)》2004,47(1)
Theelasticconstantsandtheviscositycoefficientsarethekeyparametersforthephysicalpropertiesofnematicliquidcrystals(LCs)[1,2],fortheyarecorrespondingtothethresholdvoltageandtherespondingtimeofliquidcrystaldisplaydevices[3,4].Sofarnotechniquethatcansimultaneouslymeasurethetwoparametersinsituhasbeenreported.TheelasticconstantsandviscositycoefficientsofnematicLCsatthepresentaremeasuredusingdifferentmethodsindependently.TheviscositycoefficientsisgenerallymeasuredwithOstwaldviscosimeter,andtheelasti… 相似文献
19.
F.A. Gianturco T. Mukherjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(2):211-218
The scattering of slow positrons from and NO molecules is treated using exact static interactions and a model potential for correlation-polarisation forces. The
quantum coupled equations for the elastic scattering are extended to vibrationally inelastic processes and the different excitation
probabilities are evaluated. Comparison with existing experiments for the NO target indicates that the present calculations
provide a realistic treatment of positron scattering below Ps formation and give computational estimates on the efficiency
of such projectiles in producing vibrationally excited molecules in the ambient gas.
Received: 23 April 1999 / Received in final form: 3 June 1999 相似文献
20.
M. Hohl J. Roth H.-R. Trebin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):595-601
The icosahedral or decagonal symmetry of quasicrystals is well described by a periodic structure in higher dimensions. One
consequence is the existence of dynamic phason modes in addition to the phonon modes. In an atomistic model phasons show up
as correlated atomic jumps. We detect the phasons by the calculation of correlation functions and the dynamical structure
factor in molecular dynamics simulations similar to the procedure used for phonons. In the simulations it is also possible
to observe atomic jump processes directly. The models studied here represent icosahedral AlCuLi and decagonal AlCuCo quasicrystals.
Ring processes are observed in the icosahedral case, and flips in the decagonal model.
Received 17 March 2000 and Received in final form 8 June 2000 相似文献