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1.
We present a real space renormalization group (RSRG) method to study the lattice dynamics of a three component Fibonacci (3CF)
quasicrystal. Phonon dispersion relations corresponding to different models of this lattice are obtained. Some features of
the phonon dispersion curves are compared with experiments on real quasicrystal. It is observed that the positions of the
strongest Bragg peaks calculated analytically are in perfect agreement with our RSRG calculations.
Received 23 October 2000 and Received in final form 11 January 2001 相似文献
2.
L. Elcoro J.M. Perez-Mato 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):85-89
The diffraction properties of a quenched Al-Mg alloy which has been recently termed as a “cubic quasicrystal” are quantitatively
reanalyzed. It is shown that the phase can be interpreted within the superspace formalism as an ordinary incommensurately modulated structure. The cubic six-dimensional superspace group that describes its symmetry properties has
been determined. The additional inflation symmetry features exhibited by the diffraction diagram can be summed up by its invariance
for the inflation factor , but this property has its origin in the specific value of the modulus of the modulation wave vectors, which is composition
dependent. Other particular values of this modulus can give rise to similar scaling properties. Further experiments are required
to ellucidate if the mentioned inflation symmetry is a fortuitous situation in a composition dependent wave vector, or has
indeed the physical significance which would allow to describe the system as a “cubic quasicrystal”.
Received: 25 June 1998 / Received in final form and Accepted: 23 September 1998 相似文献
3.
C. Dong Q.H. Zhang D.H. Wang Y.M. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):25-32
The composition, with an e
/
a ratio of 1.86 being close to ternary Al-Cu-TM (Transition Metal) quasicrystals, has been chosen for the search of Al-Cu approximants.
Phase structures and compositions were studied using TEM, X-ray diffraction and EPMA techniques. Two new phases were found:
face-centered orthorhombic oF-Al43.2Cu56.8 (a
= 0.816
6
, b
= 1.414
9
, c
= 0.999
5
nm) and body-centered orthorhombic oI-Al41.3Cu58.7 (oI, a
= 0.408
3
, b
= 0.707
4
, c
= 0.999
5
nm). Their e
/
a ratios are the same as that of the Al-Cu-Fe icosahedral quasicrystal. Their space groups are probably oF-Fmm2 and oI-Imm2.
Both are B2 vacancy-containing superstructures; unit cell compositions can be expressed approximately as oF-Al36Cu and oI-Al8Cu (: vacancies). They both exist in twinning variants of the types and . Such twinning modes indicate that these orthorhombic phases are the decomposition products of a high-temperature parent
phase 2-Al2Cu3, the atomic structure of which contains pentagonal atomic arrangements. Therefore the oF, oI, and phases are all B2-based approximants corresponding to the Al-Cu-TM quasicrystals.
Received: 8 July 1997 / Revised: 19 May 1998 / Accepted: 16 June 1998 相似文献
4.
G. Abramovici 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):39-44
We introduce a new Non-Orthogonal Tight-Binding model, for complex alloys, in which electronic structure is characterized
by charge transfers. We give the analytic calculation of a charge transfer, in which overlapping two-center terms are rigorously
taken into account. Then, we apply numerically this result to an approximant phase of a quasicrystal of alloy. This model is more particularly adapted to transition metals, and gives realistic densities of states.
Received: 7 July 1997 / Revised: 10 March 1998 / Accepted: 3 April 1998 相似文献
5.
We discuss the high-temperature electronic and thermal properties of an icosahedral quasicrystal within the framework of the fractional multicomponent Fermi-surface model. When intervalley electron-phonon scattering sets in above a characteristic temperature T∗ of the order of the Debye temperature ΘD the quasicrystal becomes more “metallic”. In this regime the electrical conductivity and the electronic contribution to the thermal conductivity vary as T and T2, respectively. We predict that at elevated temperatures the electronic specific heat will vary faster than γT and the low-frequency Drude-type component of the optical conductivity σ1(ω) will gain weight. 相似文献
6.
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
7.
T. Grenet M.C. Cheynet 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):701-705
We present the results of an electron energy loss spectroscopy (EELS) investigation of the icosahedral quasicrystals i-Al-Cu-Fe,
i-Al-Pd-Mn and i-Al-Pd-Re. The spectra of the three systems studied are very similar. Their main contribution comes from a
broad plasmon like peak, which can be interpreted as an “s-p" electron plasmon damped by “d" electron interband transitions. We show that it is similar to those found in other simple crystalline aluminum-transition
metal alloys, so that no specificity related to the quasicrystalline order of the alloys dominates.
Received 3 November 1998 and Received in final form 16 July 1999 相似文献
8.
R. Currat E. Kats I. Luk'yanchuk 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):339-347
We propose a simple phenomenological model describing composite crystals, constructed from two parallel sets of periodic inter-penetrating
chains. In the harmonic approximation and neglecting thermal fluctuations we find the eigenmodes of the system. It is shown
that at high frequencies there are two longitudinal sound modes with standard attenuation, while in the low frequency region
there is one propagating sound mode and an over-damped phase mode. The crossover between these two regions is analyzed numerically
and the dynamical structure factor is calculated. It is shown that the qualitative features of the experimentally observed
spectra can be consistently described by our model.
Received 28 November 2001 and Received in final form 23 January 2002 相似文献
9.
T. Grenet F. Giroud 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):165-170
We present a study of the electrical transport properties of thin i-Al-Cu-Fe films. We observe clear signatures of a dimensional
crossover in the temperature and magnetic field dependence of the conductivity for films thinner that ≃ 103?. In particular for the thinnest sample the magnetoconductivity is strongly anisotropic, as is expected for the weak localisation
contribution in two dimensions. These experiments show direct qualitative manifestations of the disorder induced quantum interference
effects occurring in quasicrystals. Estimates of the electronic microscopic parameters are in accordance with those obtained
in bulk samples. Their values and significance are discussed.
Received 16 February 2001 and Received in final form 20 June 2001 相似文献
10.
K. Schröter G. Wilde R. Willnecker M. Weiss K. Samwer E. Donth 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):1-5
High-resolution synchrotron-radiation powder diffraction experiments were performed to observe structural changes induced
by hydrogen loading in rapidly-quenched Ti-Zr-Ni alloy ribbons with dominant icosahedral character. Lattice expansion effects
due to hydrogen storage in Ti-Zr-Ni quasicrystals as well as phonon and phason disorder coefficients are obtained from an
analysis of diffraction linewidths.
Received: 26 August 1997 / Revised: 8 January 1998 / Accepted: 10 February 1998 相似文献
11.
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
12.
Atomic jumps in icosahedral (AlCu)Li quasicrystals and related structures have been studied by molecular dynamics simulations.
In quasicrystalline structures jumps exists with jump vectors much shorter than an average nearest neighbor distance. This
is a consequence of the phasonic degree of freedom. The jumps therefore are called flips and the sites connected by the jump
vector are denoted alternative positions. We find that the atoms in the quasicrystal structures studied here do not flip to
alternative positions as proposed and observed in decagonal or dodecagonal quasicrystals but jump to sites which are at least
an ordinary interatomic distance apart. Furthermore we observe two diffusion regimes: below about 55% of the melting temperature
only small (AlCu) atoms carry out ring processes whereas at higher temperatures both kinds of atoms contribute to long-range
diffusion.
Received 21 July 1999 相似文献
13.
We have studied fluid-solid phase transformations of materials interacting via the Dzugutov potential (Phys. Rev. A 46, R2984 (1992)). We present evidence from molecular dynamics simulations that this interaction does not exhibit a liquid phase.
If a mixed potential (r) is formed by a linear superposition of and the Lennard-Jones potential , then the liquid phase disappears at a fraction of less than 60% .
Received 15 June 1998 and Received in final form 8 July 1999 相似文献
14.
Y. Nishiyama 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):547-554
To investigate the influence of electronic interaction on the metal-insulator transition (MIT), we consider the Aubry-André
(or Harper) model which describes a quasiperiodic one-dimensional quantum system of non-interacting electrons and exhibits
an MIT. For a two-particle system, we study the effect of a Hubbard interaction on the transition by means of the transfer-matrix
method and finite-size scaling. In agreement with previous studies we find that the interaction localizes some states in the
otherwise metallic phase of the system. Nevertheless, the MIT remains unaffected by the interaction. For a long-range interaction,
many more states become localized for sufficiently large interaction strength and the MIT appears to shift towards smaller
quasiperiodic potential strength.
Received 17 August 1998 相似文献
15.
F. Dugain M. de Boissieu K. Shibata R. Currat T.J. Sato A.R. Kortan J.-B. Suck K. Hradil F. Frey A.P. Tsai 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):513-516
The dynamics of the decagonal AlNiCo phase has been investigated on a single-grain quasicrystalline sample using inelastic
neutron scattering. The decagonal structure can be viewed as a periodic stacking of quasiperiodic planes. The anisotropy between
the modes propagating in the periodic and quasiperiodic directions is found to be much weaker than theoretically predicted.
A strong resonance splitting is observed at an energy transfer of 15 meV for transverse modes polarized in the quasiperiodic
plane.
Received: 18 November 1998 / Accepted: 27 November 1998 相似文献
16.
N. Bouarissa 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):139-143
Pseudopotential investigation of energy band gaps and charge distribution in quasi-binary (GaSb)1-x(InAs)x crystals has been reported. To the best of our knowledge, there had been no reported theoretical work on these materials.
In agreement with experiment, the quasi-binary crystals of interest showed a significant narrowing of the optical band gap
compared to the conventional GaxIn1-xAsySb1-y quaternary alloys (with x
= 1 -
y). Moreover, the absorption at the optical gaps indicated that (GaSb)1-x(InAs)x is a direct Γ to Γ band-gap semiconductor within a whole range of the x composition. The information derived from the present study predicts that the band gaps cross very important technological
spectral regions and could be useful for thermophotovoltaic applications.
Received 30 August 2002 Published online 1st April 2003
RID="a"
ID="a"Present address: Physics Department, University of M'sila, 28000 M'sila, Algeria e-mail: N_Bouarissa@yahoo.fr 相似文献
17.
J. Roth F. Gähler 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):425-445
A molecular dynamics study of atomic self-diffusion in Frank-Kasper type dodecagonal quasicrystals is presented. It is found
that the quasicrystal-specific flip mechanism for atomic diffusion, predicted by Kalugin and Katz, indeed occurs in this system.
However, in order to be effective, this mechanism needs to be catalyzed by other defects, such as half-vacancies. For this
reason, it is difficult to distinguish from standard vacancy diffusion.
Received: 11 March 1998 / Received in final form and Accepted: 30 July 1998 相似文献
18.
It has recently been claimed that the dynamics
of long-wavelength phason fluctuations has been observed in
i-AlPdMn quasicrystals [S. Francoual et al.
Phys. Rev. Lett. 91, 225501 (2003);
A. Létoublon et al. 54, 753 (2001)]. We will show that
the data reported call for a more detailed development of
the elasticity theory of Jarić and Nelsson [M.V. Jarić and D.R. Nelsson, Phys. Rev. B 37,
4458 (1988)]
in order to determine the nature of small phonon-like atomic displacements
with a symmetry that follows the phason elastic constants.
We also show that a simple model with a single diffusing tile is sufficient
to produce a signal that (1) is situated at a “satellite position”
at a distance q from each Bragg peak; that (2) has an intensity that
scales with the intensity of the corresponding Bragg peak;
(3) falls off as 1/q2; and (4) has a time decay constant that is proportional to 1/Dq2.
It is thus superfluous to call for a picture of “phason waves” in order to explain such data, especially as such “waves” violate
many physical principles. 相似文献
19.
T. Schaub J. Delahaye C. Berger H. Guyot R. Belkhou A. Taleb-Ibrahimi Y. Calvayrac 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):183-188
High resolution photoemission measurements performed at low temperatures on a single-grained sample of the AlPdMn icosahedral
phase show that the density of states N(E) strongly depends on the nature of the surface. For an ordered quasicrystalline surface, prepared by Ar etching and ultra
high vacuum annealing, a dip feature is observed in N(E) near the Fermi level, which energy dependence can be analyzed with a simple square-root power law. By contrast, N(E) varies only little with energy both for a disordered surface and a crystalline surface of the same sample. A sharp Fermi
edge is then clearly observed. This shows that the metallic character of the surface of a quasicrystal is strongly reduced
when the surface presents a quasicrystalline ordering.
Received 19 February 2000 and Received in final form 6 November 2000 相似文献