SURFACE EFFECTS ON THE PHASE TRANSITIONS

1992 ◽  
Vol 06 (14) ◽  
pp. 2531-2547 ◽  
Author(s):  
G. BARBERO ◽  
T. BEICA ◽  
R. MOLDOVAN ◽  
A. STEPANESCU
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Surface Tension ◽  
Phase Transitions ◽  
Critical Temperature ◽  
Surface Energy ◽  
Order Parameter ◽  
Multilayer Model ◽  
Classical Models ◽  
New Form

The influence of the surface on the phase transitions is discussed. Classical models are reviewed and critically analyzed. Starting with a multilayer model, a new form of the surface energy is proposed. Our model predicts, contrary to previous models, a surface order parameter different from zero in a temperature range above the critical temperature characterizing the bulk phase transition. The application of the model to the evaluation of the surface tension gives results in agreement with experimental data.

ON THE SURFACE TENSION BEHAVIOUR NEAR THE CRITICAL TEMPERATURE

1991 ◽  
Vol 05 (11) ◽  
pp. 753-762 ◽  
Author(s):  
G. BARBERO ◽  
Z. GABBASOVA ◽  
E. MIRALDI
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Surface Tension ◽  
Critical Temperature ◽  
Order Phase Transition ◽  
Order Parameter ◽  
Landau Theory ◽  
Monotonic Trend

The surface tension near the critical temperature defining an order phase transition is theoretically analysed in the framework of a Landau theory. The considered medium is supposed to be characterized by a bulk order parameter different from zero below a critical temperature. It is shown that if the surface order parameter is different from the bulk one a non-monotonic trend of the surface tension versus the temperature is to be expected. This result agrees with published experimental data.

TEMPERATURE DEPENDENCE OF SURFACE TENSION OF LIQUID CRYSTALS AT THE PHASE TRANSITION

1995 ◽  
Vol 09 (03n04) ◽  
pp. 237-242 ◽  
Author(s):  
R. MOLDOVAN ◽  
M. TINTARU ◽  
T. BEICA ◽  
S. FRUNZA ◽  
D. N. STOENESCU
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Surface Tension ◽  
Free Energy ◽  
Surface Layer ◽  
Order Parameter ◽  
Unit Area ◽  
Negative Slope ◽  
First Order ◽  
First Order Transition

The surface tension is calculated as the excess of the free energy per unit area, due to the presence of a surface layer, using Landau–de Gennes expansions, in the hypothesis of a first order transition in the bulk and taking into account the dependence of the surface free energy from the surface tilt angle. The surface order parameter is calculated and surface-ordered phase above the phase transition temperature has been found. A variety of calculated surface tension versus temperature curves with a jump at the phase transition, with positive or negative slope, well describing the experimental data from literature, have been attained.

Two Species/Nonideal Solution Model for Amorphous/Amorphous Phase Transitions

1996 ◽  
Vol 455 ◽  
Author(s):  
Cornelius T. Moynihan
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Critical Temperature ◽  
Amorphous Phase ◽  
Thermodynamic Model ◽  
Critical Pressure ◽  
Solution Model ◽  
Amorphous Phases ◽  
First Order ◽  
Temperature And Pressure

ABSTRACTA simple macroscopic thermodynamic model for first order transitions between two amorphous phases in a one component liquid is reviewed, augmented and evaluated. The model presumes the existence in the liquid of two species, whose concentrations are temperature and pressure dependent and which form a solution with large, positive deviations from ideality. Application of the model to recent data indicates that water can undergo an amorphous/amorphous phase transition below a critical temperature Tc of 217K and above a critical pressure Pc of 380 atm.

Two-Dimensional Phase Transitions Associated with a Surface Miscibility Gap in Cu-Ag Alloys

1990 ◽  
Vol 202 ◽  
Author(s):  
Y. Liu ◽  
P. Wynblatt
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Critical Temperature ◽  
Abrupt Change ◽  
Surface Composition ◽  
Bulk Composition ◽  
Miscibility Gap ◽  
Experimental Measurements ◽  
Two Dimensional ◽  
Surface Phase

ABSTRACTA surface phase transition associated with a surface miscibility gap has been observed on the (111) surface of Cu-Ag alloys both in computer simulations and in experimental measurements of surface composition. This transition is characterized by an abrupt change in surface composition associated with changes in either bulk composition or temperature.The simulations have revealed that the transition from a Cu-rich to a Ag-rich surface phase is accompanied by interesting changes in surface structure. The experiments show that the surface critical temperature lies somewhere between 505 and 560°C.

Phase transitions in perovskites near the tricritical point: an experimental study of KMn1–xCaxF3 and SrTiO3

2000 ◽  
Vol 64 (6) ◽  
pp. 971-982 ◽  
Author(s):  
M. C. Gallardo ◽  
F. J. Romero ◽  
S. A. Hayward ◽  
E. K. H. Salje ◽  
J. del Cerro
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Phase Transitions ◽  
Order Parameter ◽  
Tricritical Point ◽  
Mean Field ◽  
Calorimetric Data ◽  
X Ray ◽  
First Order ◽  
Field Behaviour

AbstractWe present experimental data for the Pm3m-I4/mcm phase transitions in the perovskite crystals KMn1-xCaxF3 and SrTiO3. Comparison of calorimetric data (latent heat and specific heat) with order parameter data (measured with X-ray rocking methods) indicates that these transitions follow mean-field behaviour, and may be described using Landau potentials where the free energy expansion includes terms up to Q6. This potential is characteristic of transitions close to the tricritical point. Comparison of the behaviour of SrTiO3 and KMnF3 indicates that KMnF3 is closer to the tricritical point; a small amount of substitution of Ca for Mn causes the transition to cross the tricritical point from first order to second order behaviour.

scholarly journals Computer simulation of the structural phase transitions in thin ferroelectric films

2017 ◽  
Vol 07 (01) ◽  
pp. 1750004 ◽  
Author(s):  
O. G. Maksimova ◽  
A. V. Maksimov ◽  
O. S. Baruzdina
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Boundary Conditions ◽  
Order Parameter ◽  
Mixed Boundary ◽  
Structural Phase ◽  
Film Surface ◽  
Mixed Boundary Conditions ◽  
Structural Phase Transitions ◽  
Ferroelectric Films

The influence of free surface and depolarizing field on structural phase transitions in thin ferroelectric films from an ordered state to a disordered one is investigated. The dependences of the order parameter on the distance from the free film surface are calculated. It is shown that with the presence of the depolarizing field and in its absence, the effective thickness of the surface layer depends on the temperature. Nearby the phase transition point, the thickness increases indefinitely. Calculations considering depolarizing field showed that the phase transition points for the bulk ferroelectrics and the film under given boundary conditions coincide. Also shown that in the absence of depolarizing field with mixed boundary conditions, the film thickness does not affect the order parameter, and in presence of the field, this influence is observed.

A structural phase transition in NaTaOGeO4 and its relation to phase transitions in titanite

2007 ◽  
Vol 63 (4) ◽  
pp. 545-550 ◽  
Author(s):  
Thomas Malcherek
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Transition Metal ◽  
Structural Phase Transition ◽  
Order Parameter ◽  
Diffuse Scattering ◽  
Structural Phase ◽  
Group Symmetry ◽  
Critical Temperatures ◽  
Symmetry Properties

A structural phase transition from space-group symmetry P21/c to C2/c is reported for NaTaOGeO4 (NTGO). The critical temperature has been located at T c = 116 K, based on the appearance of sharp diffraction maxima at positions h + k = 2n + 1 of reciprocal space on cooling below this temperature. Strongly anisotropic diffuse scattering in sheets normal to [001] is observable for T > T c and persists up to ambient temperature. Similarities to phase transitions observed in other compounds of the titanite structure type are discussed. The symmetry properties of these phase transitions are reassessed on the basis of the structural data available. The primary order parameter is identified with the displacement of the transition metal cation M (M = Ta in NTGO) away from the centre of symmetry that it nominally occupies in the paraphase. The order parameter transforms as the Y_{2}^{-} representation. The anisotropic diffuse scattering is attributed to the one-dimensional correlation of local M displacements parallel to the direction of chains of trans-corner-sharing MO6 octahedra. The critical temperatures of the isomorphous phase transitions in various titanite-type compounds depend linearly on the squared transition-metal displacement measured in the ordered P21/c phase.

scholarly journals Elastocaloric signature of nematic fluctuations

2021 ◽  
Vol 118 (37) ◽  
pp. e2105911118
Author(s):  
Matthias S. Ikeda ◽  
Thanapat Worasaran ◽  
Elliott W. Rosenberg ◽  
Johanna C. Palmstrom ◽  
Steven A. Kivelson ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Critical Temperature ◽  
Transport Properties ◽  
Order Parameter ◽  
Low Energy ◽  
Elastic Coupling ◽  
Doping Dependence ◽  
Elastocaloric Effect ◽  
Thermodynamic And Transport Properties

The elastocaloric effect (ECE) relates changes in entropy to changes in strain experienced by a material. As such, ECE measurements can provide valuable information about the entropy landscape proximate to strain-tuned phase transitions. For ordered states that break only point symmetries, bilinear coupling of the order parameter with strain implies that the ECE can also provide a window on fluctuations above the critical temperature and hence, in principle, can also provide a thermodynamic measure of the associated susceptibility. To demonstrate this, we use the ECE to sensitively reveal the presence of nematic fluctuations in the archetypal Fe-based superconductor Ba(Fe1−xCox)2As2. By performing these measurements simultaneously with elastoresistivity in a multimodal fashion, we are able to make a direct and unambiguous comparison of these closely related thermodynamic and transport properties, both of which are sensitive to nematic fluctuations. As a result, we have uncovered an unanticipated doping dependence of the nemato-elastic coupling and of the magnitude of the scattering of low-energy quasi-particles by nematic fluctuations—while the former weakens, the latter increases dramatically with increasing doping.

scholarly journals Dynamical phase transitions and Loschmidt echo in the infinite-range XY model

2016 ◽  
Vol 374 (2069) ◽  
pp. 20150160 ◽  
Author(s):  
Bojan Žunkovič ◽  
Alessandro Silva ◽  
Michele Fabrizio
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Order Parameter ◽  
Quantum Systems ◽  
Xy Model ◽  
Time Behaviour ◽  
Dynamical Phase ◽  
Dynamical Phase Transitions ◽  
Loschmidt Echo ◽  
Infinite Range

We compare two different notions of dynamical phase transitions in closed quantum systems. The first is identified through the time-averaged value of the equilibrium-order parameter, whereas the second corresponds to non-analyticities in the time behaviour of the Loschmidt echo. By exactly solving the dynamics of the infinite-range XY model, we show that in this model non-analyticities of the Loschmidt echo are not connected to standard dynamical phase transitions and are not robust against quantum fluctuations. Furthermore, we show that the existence of either of the two dynamical transitions is not necessarily connected to the equilibrium quantum phase transition.

Evaluation of various phase-transition models for 100Cr6 for application in commercial FEM programmes

2004 ◽  
Vol 120 ◽  
pp. 581-589
Author(s):  
M. Böhm ◽  
M. Hunkel ◽  
A. Schmidt ◽  
M. Wolff
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Numerical Simulation ◽  
Heat Treatment ◽  
Phase Transitions ◽  
Research Project ◽  
Avrami Model ◽  
Transition Models

The numerical simulation of all steps of the production of a steel workpiece is nowadays a widely used tool for understanding and optimization of such processes. The transformation of austenite into ferritic phases is an important feature of heat treatment of steel. Good models for the non-isothermal phase transition are a necessary prerequisite for various other modeling steps. We evaluate some of the existing algorithms based on the isothermal Johnson-Mehl-Avrami model and compare their performance in the case of non-isothermal phase transitions with experimental data for steel 100Cr6 with exponential and linear cooling. The investigations presented here are part of a special research project on distortion engineering (SFB 570 at University of Bremen).

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