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1.
G. Saffarini 《Applied Physics A: Materials Science & Processing》2002,74(2):283-285
The glass-transition (Tg) and crystallisation (Tx) temperatures of glassy GexSeyIn12 (7≤x≤28) have been determined from differential scanning calorimetry measurements. The variations of Tg and Tx with composition have been specified. It has been found that Tg reaches a maximum at 614 K for the composition Ge23.33 Se64.67 In12 while Tx passes through a minimum at 740 K for the same composition. The values of the cohesive energies of the studied compositions
have also been estimated using the chemical bond approach method. It is found that the composition Ge23.33Se64.67In12 possesses the maximum cohesive energy. These results are explained in terms of the structure of Ge-Se-In glasses.
Received: 12 March 2001 / Accepted: 29 March 2001 / Published online: 23 May 2001 相似文献
2.
F. Krzakala O.C. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):199-208
We address the problem of chaotic temperature dependence in disordered glassy systems at equilibrium by following states of
a random-energy random-entropy model in temperature; of particular interest are the crossings of the free-energies of these
states. We find that this model exhibits strong, weak or no temperature chaos depending on the value of an exponent. This
allows us to write a general criterion for temperature chaos in disordered systems, predicting the presence of temperature
chaos in the Sherrington-Kirkpatrick and Edwards-Anderson spin glass models, albeit when the number of spins is large enough.
The absence of chaos for smaller systems may justify why it is difficult to observe chaos with current simulations. We also
illustrate our findings by studying temperature chaos in the naıve mean field equations for the Edwards-Anderson spin glass.
Received 27 March 2002 Published online 19 July 2002 相似文献
3.
Thermal analysis of Ge20Te80−xPbx (2≤x≤8) glasses has been undertaken using modulated differential scanning calorimetry (MDSC). The compositional dependence of thermal parameters is investigated. The crystallization temperatures (Tc) estimated from the total heat flow show detectable changes at compositions x=4, 6.5 and 7.5. Further, the heat capacity change at the glass transition temperature, measured from the reversible heat flow curve (ΔCpR), is found to exhibit a maximum and an inflexion at compositions x=4 and 6.5 and minimum at x=7.5, respectively. Also, the relaxation enthalpy, estimated from the area under the non-reversing heat flow curve (ΔHNR), exhibits similar features at the said compositions. From the observed MDSC results, it has been proposed that the compositions x=4 and x=6.5 denote to the onset and completion of rigidity percolation and x=7.5 corresponds to the chemical threshold of the system. 相似文献
4.
We locate the glass transition line of the charged-hard-sphere system in the density-temperature plane, using a mean-field hypernetted chain approximation within the replica-symmetry-breaking scenario [S. Franz and G. Parisi, Phys. Rev. Lett. 79 (1997) 2486. [11]]. Our results demonstrate a dominant role of the steric factor and explain the ineffectiveness of purely Coulombic interactions in driving phase transitions. 相似文献
5.
N. Mousseau D.A. Drabold 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):667-671
Many properties of alloyed chalcogenide glasses can be closely correlated with the average coordination of these compounds.
This is the case, for example, of the ultrasonic constants, dilatometric softening temperature and the vibrational densities
of states. What is striking, however, is that, at a given average coordination, these properties are nevertheless almost independent
of the elemental composition. Here, we report on some numerical verification of this experimental rule as applied to the vibrational
density of states. We find that this rule is not exact but holds qualitatively well over a wide range of compositions and
local chemical correlations.
Received 25 April 2000 相似文献
6.
S. Davatolhagh 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):291-295
The most puzzling aspect of the glass transition observed in
laboratory is the decoupling of the dynamics from the structure.
As an attempt to reconcile the dynamic and the static lengthscales
associated with the glass problem, we discuss the apparent
correlations between the static relaxation length, defined as that
lengthscale over which the potential energy fluctuation is
correlated, with the linear size of the dynamic heterogeneity. The
dynamic heterogeneous domains with long life-times, may therefore
be linked to the droplets of low potential energy, or the tightly
bound regions inside the liquid. 相似文献
7.
V. Teboul 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):111-118
Finite size effects on dynamical heterogeneity are studied in liquid silica
with Molecular Dynamics simulations using the BKS potential model. When the
system size decreases relaxation times are found to increase in accordance
with previous results in finite-size simulations and confined liquids. It
has been suggested that this increase may be related to a modification of
the spatially heterogeneous dynamics in confined liquids. In agreement with
this hypothesis we observe a decrease of the spatially heterogeneous
dynamics when the size decreases. The spatially heterogeneous dynamics is
usually characterized by the dynamical aggregation of the most or the least
mobile atoms. However we find that the decrease of the dynamical aggregation
associated to the least mobile atoms is much more important than the
decrease associated to the most mobile atoms when the size decreases. This
result associated with a slowing down of the liquid is surprising as it is
expected that the dynamical aggregation of the least mobile atoms should
increase the slowing down of the liquid dynamics. The decrease of the
heterogeneous behaviour is also in contradiction with the increase of the
spatially heterogeneous dynamics observed in liquids confined inside
nanopores. However, an increase of the non-Gaussian parameter appears both
for the confinement inside nanopores and for the finite size simulations. As
the non-Gaussian parameter is usually associated with the heterogeneous
dynamics, the increase of the non-Gaussian parameter together with a
decrease of the spatially heterogeneous dynamics is also surprising. 相似文献
8.
Mixed crystals of betaine, phosphite and betaine phosphate have been investigated using broadband di-electric spectroscopy
at frequencies 10−1Hz≤ν≤109Hz and temperatures 1.5 K≤T≤300 K for several betaine phosphate concentrationsx. For 0.2≤x≤0.65 an orientational glass state is found at low temperatures. The broad susceptibility spectra were analyzed using the
concepts of distributions of relaxation times and of distributions of energy barriers. A critical comparison of the different
approaches is given. In the mixed crystals that show antiferroelectric order at low temperatures, charge transport phenomena
are studied. The static permittivity of the proton glass-forming crystals is analyzed, in terms of effectively one- and three-dimensional
Ising models that incorporate random fields and random bonds. 相似文献
9.
G. Lahajnar I. Zupančič R. Blinc A. Zidanšek R. Kind M. Ehrensperger 《Zeitschrift für Physik B Condensed Matter》1994,95(2):243-247
A pulsed field gradient proton spin-echo NMR self-diffusion study of organic glasses COANP, MBANP, PNP and NPP in their liquid and weakly supercooled states was performed. The NMR phase diagrams, based on the proton NMR transverse relaxation time (T
2) temperature hysteresis data of these materials, clearly give evidence of the onset of a glass phase on cooling the isotropic liquids below their respective melting temperatures. The self-diffusion data exhibit in the supercooled glassy state a non-Arrhenius behaviour and can be described in terms of the Vogel-Fulcher modification of the Arrhenius law,D=D
exp{–E
a
/[k
B
(T–T
VF
)]}. The activation energiesE
a
and Vogel-Fulcher temperaturesT
VF
are 83.2 meV and 239 K for COANP, 66 meV and 249 K for MBANP, and 85 meV and 245 K for PNP, respectively. The flow viscosity data obtained for COANP in the same temperature region as well conform to the Vogel-Fulcher behaviour, exp{E
a
()
/[k
B
(T–T
VF
)]}, withE
a
()
=80.4 meV andT
VF
=239 K. In case of COANPD was found to increase with decreasing diffusion time in the supercooled (glassy) melt just belowT
M
whereas no such behaviour was found aboveT
M
. 相似文献
10.
Local atomic structures of Zr100−xNix (x=33.3, 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr-Ni bond length, RZr-Ni, keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr64Ni36 metallic glass consist of Zr2Ni-like and ZrNi-like CSROs. 相似文献
11.
Roth CB Pound A Kamp SW Murray CA Dutcher JR 《The European physical journal. E, Soft matter》2006,20(4):441-448
We have used transmission ellipsometry to measure the glass transition temperature, Tg, of freely-standing films of atactic and syndiotactic poly(methyl methacrylate) (PMMA). We have prepared films with different
molecular weights, MW, (159×103 < M
w < 1.3×106) and film thicknesses, h, ( 30nm < h < 200 nm). For the high-MW ( M
w > 509×103) atactic PMMA films, we find that Tg decreases linearly with decreasing h, which is qualitatively similar to previous results obtained for high-MW freely-standing polystyrene (PS) films. However,
the overall magnitude of the Tg reduction is much less (by roughly a factor of three) for the high-MW freely-standing PMMA films than for freely-standing
PS films of comparable MW and h. The observed differences between the freely-standing PMMA and PS film data suggest that differences in chemical structure
determine the magnitude of the Tg reduction and we discuss the possible origins of these differences. Our analysis of the MW-dependence of the Tg reductions suggests that the mechanism responsible for the MW-dependent Tg reductions observed in the high-MW freely-standing films is different than that responsible for the MW-independent Tg reductions observed in the low-MW freely-standing and supported films. 相似文献
12.
A. H. Cai X. Xiong Y. Liu H. Chen W. K. An X. S. Li Y. Zhou Y. Luo 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):147-151
We propose expressions for the estimation of the isenthalpic temperature T
0 (T
0 = αT
m
, α is a semi-empirical parameter and 0 ⩽ α < 1, T
m
is the solidus temperature) and the Kauzmann temperature T
k
(T
k
= T
m
exp(α−1)) for glass forming alloys. It is found that T
k
estimated by T
k
= T
m
exp(α−1) is in agreement with that directly calculated from the heat capacity data, indicating that T
k
= T
m
exp(α − 1) can be used to estimate T
k
of glass forming alloys. T
0 estimated by T
0 = αT
m
, on the other hand, widely deviates from that of directly calculated from the heat capacity data. This suggests that the
enthalpy difference of the under-cooled liquid and the crystal might be a nonlinear function of the temperature below T
k
. Moreover, the Gibbs free energy difference ΔG is not sensitive to the deviation of α. 相似文献
13.
A.E. Allahverdyan Th.M. Nieuwenhuizen D.B. Saakian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):317-335
In a p-spin interaction spherical spin-glass model both the spins and the couplings are allowed to change with time. The spins are
coupled to a heat bath with temperature T, while the coupling constants are coupled to a bath having temperature TJ. In an adiabatic limit (where relaxation time of the couplings is much larger that of the spins) we construct a generalized
two-temperature thermodynamics. It involves entropies of the spins and the coupling constants. The application for spin-glass
systems leads to a standard replica theory with a non-vanishing number of replicas, n=T/T
J
. For p>2 there occur at low temperatures two different glassy phases, depending on the value of n. The obtained first-order transitions have positive latent heat, and positive discontinuity of the total entropy. This is
an essentially non-equilibrium effect. The dynamical phase transition exists only for n<1. For p=2 correlation of the disorder (leading to a non-zero n) removes the known marginal stability of the spin glass phase. If the observation time is very large there occurs no finite-temperature
spin glass phase. In this case there are analogies with the non-equilibrium (aging) dynamics. A generalized fluctuation-dissipation
relation is derived.
Received 12 July 1999 and Received in final form 8 December 1999 相似文献
14.
We show the existence of precursors of crystalline and amorphous phases preceding the appearance of freezing and glass transitions in colloidal systems. The formation of crystalline clusters or amorphous local arrangements can be controlled by tuning the parameters of a proposed continuous potential and by changing the packing conditions. 相似文献
15.
A. Díaz-Sánchez A. Pérez-Garrido 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):483-486
The relaxation of the specific heat and the entropy to their equilibrium values is investigated numerically for the three-dimensional
Coulomb glass at very low temperatures. The long time relaxation follows a stretched exponential function, f (t) = f
0exp - (t/τ)β
, with the exponent β increasing with the temperature. The relaxation time diverges as an Arrhenius law when T→ 0.
Received 24 May 2001 and Received in final form 12 September 2001 相似文献
16.
We consider an Ising competitive model defined over a triangular Husimi tree where loops, responsible for an explicit frustration, are even allowed. We first analyze the phase diagram of the model with fixed couplings in which a “gas of noninteracting dimers (or spin liquid) — ferro or antiferromagnetic ordered state” zero temperature transition is recognized in the frustrated regions. Then we introduce the disorder for studying the spin glass version of the model: the triangular ±J model. We find out that, for any finite value of the averaged couplings, the model exhibits always a finite temperature phase transition even in the frustrated regions, where the transition turns out to be a glassy transition. The analysis of the random model is done by applying a recently proposed method which allows us to derive the critical surface of a random model through a mapping with a corresponding nonrandom model. 相似文献
17.
We present an experimental investigation of the Generalized Einstein Relation (GER), a particular form of a fluctuation-dissipation relation, in an out-of-equilibrium visco-elastic fluid. Micrometer beads, used as thermometers, are immersed in an aging colloidal glass to provide both fluctuation and dissipation measurements. The deviations from the Generalized Einstein Relation are derived as a function of frequency and aging time. The observed deviations are interpreted as directly related to the change in the glass relaxation times with aging time. In our scenario, deviations are observed in the regime where the observation timescale is of the order of a characteristic relaxation time of the glass. 相似文献
18.
The relaxation processes (α, β, and γ) in UHMW PE fibres drawn to different draw ratios λ have been studied by dynamic-mechanical and nuclear magnetic resonance methods. The temperature dependences of tensile loss
moduli E″ and spin-lattice relaxation times T
1 have been analyzed assuming distribution of correlation times τ according to the Davidson—Cole function. The activation energies E
a and parameters ε characterizing widths of distribution, and asymptotic value τ
0 for correlation times have been determined from experimental data for low-temperature γ-process and for high-temperature α-process. A weak β-process has been found by dynamic-mechanical method and quantitative analysis was made only for fibres with λ = 9. The temperature dependences of second moment M
2 of the broad-line NMR spectra have been analyzed according to the Gutowsky—Pake formula, which includes only a single correlation
time τ
c without distribution. In this case the activation energies E
a and values of τ
0 have been determined. 相似文献
19.
For the supercooled salt melt 0.4 Ca(NO3)2–0.6 KNO3 the photoacoustic amplitude and phase shift are measured in the glass transition region. The transition temperature is defined by the maximum in the phase angle. It is shifted to lower temperatures for lower frequencies. A frequency-dependent specific heat can be calculated from the data in the dispersion region. The frequency dependence of the transition temperature can be fitted by a power law with exponent =8.8±1.This work is part of a Ph. D. thesis at the Technische Universität München 相似文献
20.
Lithium cesium mixed alkali borate glasses of the composition 67B2O3·xLi2O·(32−x)Cs2O (where x=8, 12, 16, 20 and 24) containing 1 mol% Nd2O3 were prepared by melt quenching. The absorption spectra of Nd3+ were studied from the experimental oscillator strengths and the Judd-Ofelt intensity parameters were obtained. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) (AT), branching ratios (β) and integrated absorption cross-sections (Σ) of the Nd3+ transitions from the excited state J manifolds to the lower lying J′ manifolds. Radiative lifetimes (τR) are estimated for certain excited states of Nd3+ in these mixed alkali borate glasses. Luminescence spectra were measured and the emission cross-sections (σp) were evaluated for the three emission transitions. The variation of luminescence intensity with x was recorded for the three transitions at different excitation power to see the effect of mixed alkalies in these borate glasses. 相似文献