共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Moret P. Launois T. Wågberg B. Sundqvist 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):253-263
Two-dimensional polymerisation of a C60 single crystal has been obtained under high-pressure high temperature conditions (700 K - 2 GPa). Crystalline order is preserved
but the crystal splits into variants (orientational domains). The analysis of X-ray diffraction and Raman spectroscopy data
reveals that the polymer crystal is primarily tetragonal with some admixture of rhombohedral phase. Furthermore, Raman spectroscopy
gives evidence for additional C60-C60 dimers, which are probably disordered. For the tetragonal phase, it is shown that successive polymer layers are rotated by
about the stacking axis, according to the P42/mmc space group symmetry. The structure of the rhombohedral phase is also clarified. The role of the interlayer interactions
in stabilising the two-dimensional polymer phases of C60 is discussed.
Received 8 October 1999 相似文献
2.
A. Bernert T. Chatterji P. Thalmeier P. Fulde 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):535-546
We report results of a new analysis for the low-temperature structure of α
′
-NaV2O5 from synchrotron X-ray diffraction experiments. We confirm the existence of two inequivalent ladder structures in each vanadium
layer. Based on our structural data we perform a bond-valence calculation for the vanadium sites in the low temperature state.
Due to an asymmetric charge ordering we obtain only two different vanadium valences despite the three inequivalent sites.
This explains the 51V-NMR observation of only two resonant peaks in the charge ordered phase. By use of a Slater-Koster method to obtain hopping
matrix elements and cluster calculations we obtain effective vanadium-vanadium hoppings which compare well to LDA results.
Using these in a cluster calculation we obtain a superexchange of 0.047 eV between electrons on neighbouring rungs of the same ladder for the undistorted phase. For the distorted phase we find
a significant alternation in the shifts of the oxygen atoms along the legs of one of the two ladder types which leads to a
significant exchange dimerisation δ
J
≈ 0.25.
Received 24 November 2000 相似文献
3.
J. Badro J.P. Itié A. Polian 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):265-268
X-ray diffraction (XRD) experiments have been carried out on quartz-like GaPO4 at high pressure and room temperature. A transition to a high pressure disordered crystalline form occurs at 13.5 GPa. Slight
heating using a YAG infrared laser was applied at 17 GPa in order to crystallize the phase in its stability field. The structure
of this phase is orthorhombic with space group Cmcm. The cell parameters at the pressure of transition are a
=7.306?, b
=5.887? and c
=5.124?.
Received: 7 October 1997 / Received in final form: 17 November 1997 / Accepted: 18 November 1997 相似文献
4.
D. Le Pévelen J. Gaultier Y. Barrans D. Chasseau F. Castet L. Ducasse 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):363-373
The crystal structure of (TMTSF)2ClO4 has been determined at (7 K, 1 bar) and at (7 K, 5 kbar) with a high accuracy. For the latter, low temperature and pressure
were applied simultaneously using a X-ray diffraction instrumentation designed in our laboratory, these results are the first
for molecular compounds. The effects of lowering the temperature are not the same as those produced by increasing the pressure.
At (7 K, 1 bar) the anion ordering which occurs in this compound, and which is characterised by the appearance of b
*
/2 superlattice reflections, is well observed. This anion ordering leads to the presence of two independent stacks of TMTSF
cations which is the only case found in the Bechgaard salts family. The comparison of the low temperature crystal structures
under atmospheric pressure and at 5 kbar shows that the centres of mass are nearly the same, independent of the pressure:
the interchain interactions do not depend on the doubling of the unit cell. Under pressure, the ordering (0, 1/2, 0) does
not occur at any temperature. These structural data are confirmed by the quantum chemical calculations which show that the
difference in the site energy of the two independent cations is 100 meV.
Received 10 April 2000 and Received in final form 27 September 2000 相似文献
5.
After classifying amorphous materials according to their topology, we review a recently proposed theory of pressure amorphization
(PA) that arises from some degree of displacive disorder while retaining a crystalline topology. That theory is based on the
notion that one or more branches of the phonon spectrum become soft and flat with increasing pressure and is illustrated by
a simple model that possesses the range of features displayed by many of the materials which undergo PA with displacive disorder.
We report the results of Langevin simulations of the simple model which show how the probability of amorphization increases
with the number of unit cells in the system and support our theory. We comment on how to generalize the model for the study
of real systems.
Received 29 march 2002 相似文献
6.
V. Dureuil C. Ricolleau M. Gandais C. Grigis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):83-88
The crystalline structure of Co clusters embedded in an amorphous Al2O3 matrix was studied by transmission electron microscopy (TEM) and electron diffraction (TED). In the first stage of the growth
a metastable structure (body-centred-cubic) is observed. A face-centred-cubic phase (fcc) is found when the size of the clusters
increases ( diameter > 4 nm). The hexagonal-close-packed phase arises in the fcc phase by a succession of stacking faults at the largest sizes.
The mechanisms of phase transformation have been determined by using high resolution electron microscopy (HREM). The chemical
nature of the clusters, in particular the existence of Co-O bonds, was investigated by using electron energy loss spectroscopy
(EELS).
Received 03 July 2000 and Received in final form 22 December 2000 相似文献
7.
J. Kästner W. Petry S.M. Shapiro A. Zheludev J. Neuhaus Th. Roessel E.F. Wassermann H. Bach 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):641-648
The acoustic phonon dispersions of two Invar crystals , one ordered with the () structure, the other disordered fcc, have been investigated between 3.4 K and 470 K by inelastic and elastic neutron scattering.
For the ordered crystal, pronounced softening of the whole
phonon branch is observed on cooling below the Curie temperature. Particularly strong phonon softening at the M-point zone
boundary of the structure leads to a displacive, antiferrodistortive phase transition at low temperatures. For the disordered crystal, much
weaker softening of the
phonons is observed and restricted to the region near the Brillouin zone center, where increasing elastic scattering with
decreasing temperature indicates the growth of local tetragonal strain. This strain is considered as a typical precursor of
the transformation to bct martensite. Specific heat measurements, performed at low temperatures on both crystals confirm the
neutron scattering results and reveal considerable enhancement of the low energy phonon density of states in the ordered crystal.
Received 18 January 1999 相似文献
8.
X. Wu Z. Wu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):521-526
First-principles calculations based on density functional
theory were used to study the high-pressure phases of both ZnF2 and
CdF2. We found that the sequence of the pressure-induced phase
transitions is: Rutile (P42/mnm) ↦ CaCl2 (Pnnm) ↦ PdF2
(Pa-3) and CaF2 (Fm3m) ↦ PbCl2 (Pnma) ↦ Ni2In
(P63/mmc) for ZnF2 and CdF2 respectively. In ZnF2 the
behavior of the ground-state total energy, of the Gibbs free energy and of
the lattice constant vs. pressure shown that the phase transition at 4 GPa
from the rutile-type phase to the CaCl2-type phase is a second-order
phase transition. The mechanism of the structural change was also revealed
by the transition from the PbCl2-type phase to the Ni2In-type
phase in CdF2. Moreover, the high-pressure behavior of divalent metal
fluorides was compared and discussed. 相似文献
9.
P. Foury-Leylekian J.P. Pouget M. Greenblatt E. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):157-167
We present a structural investigation of the family of quasi-one-dimensional (quasi-1D) conductors, which exhibit intriguing charge transport properties where, for x small, the conductivity exhibits a crossover from a semiconducting to a metallic like regime when the temperature decreases.
In these materials the double zig-zag chains, together with the diphosphate groups, delimit channels which are partially filled with the ions. It is found, from an X-ray diffuse scattering investigation, that at room temperature the ions are locally ordered on a lattice of well-defined sites in the channel direction and not ordered between neighboring
channels. These ions form 1D incommensurate concentration waves whose periodicity depends on the stoichiometry. In upon cooling, the intrachannel order increases significantly, and an interchannel order between the 1D concentration waves develops. But, probably because of kinetic effects, no tridimensional (3D) long range order of the ions is achieved at low temperature. The 3D low-temperature local order has been determined and it is found that the phase
shift between the concentration waves minimizes their Coulomb repulsions. This local order is increasingly reduced as the Cs concentration
diminishes. We interpret the intriguing features of the electrical conductivity in relationship with the thermal evolution
of the Cs ordering effects. We suggest that in , for x small, a localization-delocalization transition of the Anderson type occurs due to the thermal variation of the Cs disorder.
When x increases, the enhancement of the disorder leads to a localization of the electronic wave function in the whole temperature
range measured. Finally, and probably because of the disorder, no charge density wave instability is revealed by our X-ray
diffuse scattering investigation.
Received: 10 October 1997 / Received in final form: 11 December 1997 /
Accepted: 16 December 1997 相似文献
10.
11.
R. Clérac M. Fourmigué J. Gaultier Y. Barrans P.A. Albouy C. Coulon 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):445-459
The physical properties of paramagnetic Mo(V) organometallic radical cation salts, , are investigated through the study of two series of solid solutions incorporating two kinds of anions ( or ). The combination of EPR and X-ray diffraction is used to specify the nature of the structural phase transitions which occur
in the paramagnetic phase and to determine the corresponding (
T
,
x
) phase diagrams. Finally, antiferromagnetic resonance is studied to probe the low temperature antiferromagnetic ground state.
In the last part of the paper, the observed complex phase diagram is analyzed by considering a compressible model with at
least two independent modes of compression. We conclude that the larger compressibilities are associated with the smaller
anions.
Received 5 August 1998 相似文献
12.
D. Varshney G. Joshi 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):523-534
The present paper addresses the high-pressure phase transformation and
mechanical properties of Ga1-xInxAs (x = 0.25, 0.5 and 0.75) by
formulating an effective interionic interaction potential. This potential
consists of the long-range Coulomb and charge transfer caused by the
deformation of the electron shells of the overlapping ions and the
Hafemeister and Flygare type short-range overlap repulsion extended upto the
second neighbor ions and the van der Waals (vdW) interaction. The estimated
values of phase transition pressure and the vast volume discontinuity in
pressure-volume (PV) phase diagram indicate the structural phase transition
from zinc blende (B3) to rock salt (B1). The equation of state curves plotted
between V (P)/ V (0) and pressure are for both the zincblende (B3) and rocksalt
(B1) structures. Further, the variations of the second and third order
elastic constants with pressure have followed a systematic trend, which are
almost identical to those exhibited by the observed data measured for other
compounds of this family. 相似文献
13.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献
14.
B. Pongs T. Wokrina S. Matejcek C. Buschhaus E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):289-297
The quasi-one dimensional pyrene (PY) organic conductor (PY)7(PY)4(AsF6)4
. 4CH2Cl2shows parallel as well as 60° rotated PY radical cations in its stacks, but crystallizes in two different modifications I and II. One of the seven intra-stack
pyrene molecules is susceptible to a reorientation by 60°, that is stable already at room temperature for modification II, but occurs at a hysteretic first order transition between
170 K and 240 K for modification I. Crystal structure, microwave conductivity and static magnetic susceptibility are typical
for a quasi-one dimensional organic conductor with Peierls transition at TP = 73 K (mod. I) or TP = 105 K (mod. II). The pyrene radical packing is analysed by continuous wave and pulsed electron spin resonance measurements,
using 9.45 GHz as well as 425 MHz as measuring frequency. Anisotropy of the conduction electron diffusion constant exceeds
1000 in the metallic phase.
Received 22 March 2002 Published online 31 July 2002 相似文献
15.
K. Knorr L. Ehm M. Hytha B. Winkler W. Depmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):297-303
The high-pressure behaviour of PbS was investigated by angular dispersive X-ray powder diffraction up to pressures of 6.8
GPa. Experiments were accompanied by first principles calculations at the density functional theory level. By combining both
methods reliable data for the elastic properties of rock-salt type α- and high-pressure β-PbS could be obtained. β-PbS could be determined to crystallise in the CrB-type (B33), with space group Cmcm. The reversible ferro-elastic α/β transition is of first order. It is accompanied by a large volume discontinuity of about 5% and a coexistence region of the
two phases. A gliding mechanism of {001} bilayers along one of the cubic 〈110〉 directions governs the phase transition which can be described in terms of group/subgroup relationships via a common subgroup, despite its reconstructive character. The quadrupling of the primitive unit cell indicates a wave vector
(0, 0,π/
a
) on the Δ-line of the Brillouin zone.
Received 11 October 2002 Published online 14 February 2003
RID="a"
ID="a"Also at: Institute of Physics of the Czech Academy of Sciences, Cukrovarnicka 10, 16253 Praha 6, Czech Republic e-mail: knorr@min.uni-kiel.de
RID="b"
ID="b"Present address: University of Cambridge, Cavendish Laboratory (TCM), Madingley Road, Cambridge CB3 0HE, UK
RID="c"
ID="c"Present address: Johann-Wolfgang Goethe Universit?t, Mineralogisches Institut, Kristallographie, Senckenberganlage 30, D 60054 Frankfurt a.M.,
Germany 相似文献
16.
E.A. Smirnova P.A. Korzhavyi Yu. Kh. Vekilov B. Johansson I.A. Abrikosov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):57-66
We report on a detailed investigation of the phase equilibria and the Fermi surface in the Al-Zn system. Our calculation are
based on the density functional theory and we use the linear muffin-tin orbital method and the Green's function technique.
The calculated free energies of alloy formation exhibit the existence of a miscibility gap between the alloys containing approximately
10 and 55 at.% of Zn, in agreement with the phase diagram of the Al-Zn system. Seven electronic topological transitions (ETT)
were found in Al-Zn system within the stability range of the fcc solid solution. A relation between these ETT and the phase
stability of the fcc Al-Zn solid solutions is established. We show that extremum points on the concentration dependencies
of the thermodynamic properties of Al-Zn alloys can be explained by band-filling effects.
Received 6 February 2002 Published online 19 November 2002 相似文献
17.
The lifetime of the soliton in the improved Davydov model at the biological temperature 300 K for protein molecules 总被引:7,自引:0,他引:7
Pang Xiao-feng 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):297-316
We study the effects of quantum fluctuations and thermal perturbations on the lifetime of the soliton in the improved Davydov
model proposed by us with two-quanta and with an added interaction. By using quantum perturbation theory, we compute the soliton
lifetime for a wide ranges of parameter values relevant for protein molecules. The lifetime of the new soliton at the biological
temperature 300 K is of the order of 10-10 second or τ/τ≥ 500 for parameters appropriate to α-helical protein molecules. This shows clearly that the new soliton in the improved model
is a viable mechanism for the bio-energy transport in the α-helix region of proteins.
Received 7 January 1999 and Received in final form 16 August 2000 相似文献
18.
F. Bourdarot A. Bombardi P. Burlet R. Calemczuk G.H. Lander F. Lapierre J.P. Sanchez K. Mattenberger O. Vogt 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):605-611
We report specific heat and neutron diffraction measurements of seven samples in the solid solution system UxLa1-xS. All samples have the simple fcc NaCl crystal structure. Both specific heat and neutron diffraction confirm the suggestion
from the earlier magnetic measurements that the ferromagnetism disappears abruptly at 0.57. Near there is a doubling of the electronic contribution to the specific heat, as compared to the value of 23 mJ mol-1K-2 in pure US. Around the widths of the nuclear Bragg peaks show a considerable broadening, as well as anomalies in the mean lattice parameter,
as compared to those expected from Vegard's law. A preliminary analysis suggests this broadening may be due to a loss of long
range lattice order near . However, these changes are independent of temperature, so that further experiments are necessary before they can be associated
with the changes in magnetic behavior at .
Received 18 September 1998 相似文献
19.
S. Hémon A. Berthelot Ch. Dufour F. Gourbilleau E. Dooryhée S. Bégin-Colin E. Paumier 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):517-523
The irradiation effects induced by swift heavy ions are now widely described in `bulk' materials. It is shown here that the
behaviour of matter under irradiation depends on its crystalline state in the sense that a given material is all the more
sensitive to swift heavy ion irradiations as the mean crystallite size L is small. The present paper relates the experimental results obtained in yttrium oxide from `in situ' X-ray diffraction measurements. Three kinds of sample have been irradiated: sintered samples (L = 1μm), non-ground powders (L = 45 nm) and ground powders (L = 28 nm). A cubic to monoclinic phase transformation appears if the electronic energy loss of the incident particle is higher
than a threshold. The comparison between the different kinds of samples reveals that this phase transformation is all the
easier as the mean crystallite size of the target is weak.
Received 27 January 2000 and Received in final form 13 December 2000 相似文献
20.
We present a calculation of the neutrino-nucleon scattering cross-section which takes into account the nuclear correlations
in the relativistic random phase approximation (RPA). Our approach is based on a quantum-hadrodynamics model with exchange
of σ, ω, π, ρ and δ mesons. In view of applications to neutrino transport in the final stages of supernova explosion and proto-neutron
star cooling, we study the evolution of the neutrino mean free path as a function of density, proton-neutron asymmetry and
temperature. Special attention was paid to the issues of renormalization of the Dirac sea, residual interactions in the tensor
channel, coupling to the delta-meson and meson mixing. In contrast with the results of other authors, we find that the neutral-current
process is not sensitive to the strength g' of the residual contact interaction. As a consequence, it is found that RPA corrections with respect to the mean-field approximation
amount to only 10% to 15% at high density.
Received: 27 June 2001 / Accepted: 14 January 2002 相似文献