Search

© 2006 The American Physical Society. We thank R. de Nalda, T.S. Grigera, G. Parisi, and C. Toninelli for discussions. P.V. was supported by the EC Contract No. MCFI-2002-01262. We were partly supported by MEC Spain, through Contracts Nos. BFM2003-08532, FIS2004-05073, and FPA2004-02602. The total CPU time devoted to the simulation carried out at BIFI PC clusters amounts to ten years of 3 GHz Pentium IV., We show numeric evidence that, at low enough temperatures, the potential energy density of a glass-forming liquid fluctuates over length scales much larger than the interaction range. We focus on the behavior of translationally invariant quantities. The growing correlation length is unveiled by studying the finite-size effects. In the thermodynamic limit, the specific heat and the relaxation time diverge as a power law. Both features point towards the existence of a critical point in the metastable supercooled liquid phase., EC, MEC (Spain), Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

© 2014 American Physical Society. Artículo firmado por 24 autores. The Janus project has been partially supported by the EU (FEDER funds, Grant No. UNZA05-33-003, MEC-DGA, Spain); by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013, ERC Grant agreement N. 247328); by the MICINN (Spain) (Contracts No. FIS2006-08533, No. FIS2012-35719-C02, No. FIS2010-16587, and No. TEC2010-19207); by the SUMA project of INFN (Italy); by CAM (Spain); by the Junta de Extremadura (GR10158); by the Microsoft Prize 2007 and by the European Union (PIRSES-GA-2011-295302). F.R.-T. was supported by the Italian Research Ministry through the FIRB Project No. RBFR086NN1; M.B.-J. was supported by the FPU program (Ministerio de Educación, Spain); R.A.B. and J.M.-G. were supported by the FPI program (Diputación de Aragón, Spain); S.P.-G. was supported by the ARAID foundation; finally, J.M.G.-N. was supported by the FPI program (Ministerio de Ciencia e Innovación, Spain)., We study the off-equilibrium dynamics of the three dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses., Unión Europea. FP7, EU (FEDER funds), Ministerio de Ciencia e Innovación (MICINN), INFN (Italy), CAM (Spain), Junta de Extremadura, Microsoft Prize 2007, European Union, Italian Research Ministry, Ministerio de Educación (Spain) under FPU program, Diputación de Aragón (Spain) under FPI program, ARAID foundation, Ministerio de Ciencia e Innovación (Spain) under FPI program, Depto. de Física Teórica, Fac. de Ciencias Físicas, TRUE, pub

The particle motion associated to the a-relaxation in supercooled liquids is still challenging scientists due to its difficulty to be probed experimentally. By combining synchrotron tech- niques, we report the existence of microscopic structure-dynamics relationships in Pt42.5 Cu27 Ni 9.5P 21 and Pd 42.5Cu 27 Ni9.5 P21 liquids which allows us to disentangle structural and kinetic contributions to the a-process. While the two alloys show similar kinetic fragilities, their structural fragilities differ and correlate with the temperature dependence of the stretching parameter describing the decay of the density fluctuations. This implies that the evolution of dynamical heterogeneities in supercooled alloys is determined by the rigidity of the melt structure. We find also that the atomic motion not only reflects the topological order but also the chemical short-range order, which can lead to a surprising slowdown of the a- process at the mesoscopic length scale. These results will contribute to the comprehension of the glass transition, which is still missing., We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III beamline P02.1 and we would like to thank Alexander Schoekel and Michael Wharmby for assistance. Further we want to thank our colleagues B. Adam, L. Ruschel, S.S. Riegler, H. Jiang, V. Lemkova, H. Voigt and J. Schmauch for collaboration and fruitful discussions concerning the topic. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and inno- vation programme (Grant Agreement No 948780). The research activity has been sup- ported by the project CALIPSOplus under the Grant 307 Agreement 730872 from the EU Framework Program for Research 308 and Innovation HORIZON 2020. The authors declare that they have no competing interests. All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials., Peer Reviewed, Postprint (published version)

Numerous experimental data on the rapid solidification of eutectic systems exhibit the formation of metastable solid phases with the initial (nominal) chemical composition. This fact is explained by suppression of eutectic decomposition due to diffusionless (chemically partitionless) solidification beginning at a high but a finite growth velocity of crystals. A model considering the diffusionless growth is developed in the present work to analyze the atomic diffusion ahead of lamellar eutectic couples growing into supercooled liquid. A general solution of the model is presented from which two regimes are followed. The first presents a diffusion-limited regime with the existence of eutectic decomposition if the solid–liquid interface velocity is smaller than the characteristic diffusion speed in the bulk liquid. The second shows suppression of eutectic decomposition under diffusionless transformation from liquid to one-phase solid if the solid–liquid interface velocity overcomes characteristic diffusion speed in the bulk liquid. © 2020 The Authors. Mathematical Methods in the Applied Sciences published by John Wiley & Sons Ltd.

An efficient description of the structures of liquids and, in particular, the structural changes that happen with liquids on supercooling remains to be a challenge. The systems composed of soft particles are especially interesting in this context because they often demonstrate non-trivial local orders that do not allow to introduce the concept of the nearest-neighbor shell. For this reason, the use of some methods, developed for the structure analysis of atomic liquids, is questionable for the soft-particle systems. Here we report about our investigations of the structure of the simple harmonic-repulsive liquid in 3D using the triple correlation function (TCF), i.e., the method that does not rely on the nearest neighbor concept. The liquid is considered at reduced pressure (P = 1.8) at which it exhibits remarkable stability against crystallization on cooling. It is demonstrated that the TCF allows addressing the development of the orientational correlations in the structures that do not allow drawing definite conclusions from the studies of the bond-orientational order parameters. Our results demonstrate that the orientational correlations, if measured by the heights of the peaks in the TCF, significantly increase on cooling. This rise in the orientational ordering is not captured properly by the Kirkwood's superposition approximation. Detailed considerations of the peaks' shapes in the TCF suggest the existence of a link between the orientational ordering and the slowdown of the system's dynamics. Our findings support the view that the development of the orientational correlations in liquids may play a significant role in the liquids' dynamics and that the considerations of the pair distribution function may not be sufficient to understand intuitively all the structural changes that happen with liquids on supercooling. In general, our results demonstrate that the considerations of the TCF are useful in the discussions of the liquid's structures beyond the pair dens

Amorphous alloys of the (Fe-Co-Ni)-(Cr-Mo-Nb)-B system are promising materials to supply the demands for higher wear resistance components in the petrochemical industry. Since the development of the CALPHAD method, the development of new metallic alloys has been accompanied by thermodynamic modelling and calculations. The prediction of the formation of amorphous alloys requires special care with the modeling of the liquid and or an amorphous phase. As a initial stage in the more complex system, the basic Fe-Nb-B ternary system was selected. In order to predict the stability and tendencies of transformations of these amorphous alloys, the Fe-Nb-B system was reassessed using Ågren's two-state model to describe the liquid phase. The results of the present assessment show very good agreement with the recently reported stable phase diagram. Furthermore, the use of the two-state model for the liquid is more accurate and physically consistent when evaluating transformations from supercooled liquid, as shown it the present work., QC 20200420

The fragility works as a fundamental concept characterizing glass-forming liquids, whereas its atomic structural interpretation remains a challenge. Herein, viscosity behaviors in polyethylene (PE), S, Se, and Te are examined, which consist of distorted chain molecules with varied interchain strength, in comparison with that in SiO2, a typical strong material. Among the 1D materials, S and PE appear to be fairly strong. Such results suggest that the viscosity exhibits Arrhenius-type behaviourif it is governed by single microscopic mechanisms such as Si-O bond scission or interchain slippages. In contrast, Se and Te appear fragile with non-Arrhenius variations, which could be ascribable to mixed inter- and intrachain interactions. Among these floppy materials, it is known that Se is the best glass former, the reason being discussed.

The fragility works as a fundamental concept characterizing glass-forming liquids, whereas its atomic structural interpretation remains a challenge. Herein, viscosity behaviors in polyethylene (PE), S, Se, and Te are examined, which consist of distorted chain molecules with varied interchain strength, in comparison with that in SiO2, a typical strong material. Among the 1D materials, S and PE appear to be fairly strong. Such results suggest that the viscosity exhibits Arrhenius-type behaviourif it is governed by single microscopic mechanisms such as Si-O bond scission or interchain slippages. In contrast, Se and Te appear fragile with non-Arrhenius variations, which could be ascribable to mixed inter- and intrachain interactions. Among these floppy materials, it is known that Se is the best glass former, the reason being discussed.

Understanding the physics of glass formation remains one of the major unsolved challenges of condensed matter science. As a material solidifies into a glass, it exhibits a spectacular slowdown of the dynamics upon cooling or compression, but at the same time undergoes only minute structural changes. Among the numerous theories put forward to rationalize this complex behavior, Mode-Coupling Theory (MCT) stands out as a unique framework that provides a fully first-principles-based description of glass phenomenology. This review outlines the key physical ingredients of MCT, its predictions, successes, and failures, as well as recent improvements of the theory. We also discuss the extension and application of MCT to the emerging field of non-equilibrium active soft matter.

Few general models representing certain classes of real glass-forming systems play a special role in computer simulations of supercooled liquid and glasses. Recently, it was shown that one of the most widely used model glassformers - the Kob-Andersen binary mixture - crystalizes in quite lengthy molecular dynamics simulations, and moreover, it is in fact a very poor glassformer at large system sizes. Thus, our understanding of crystallization stability of model glassformers is far from complete due to the fact that relatively small system sizes and short time scales have been considered so far. Here we address this issue for two embedded atom models intensively used last years in numerical studies of Cu-Zr-(Al) bulk metallic glasses. Exploring the structural evolution of Cu64.5Zr35.5 and Cu46Zr46Al8 alloys at continuous cooling and isothermal annealing, we observe that both systems nucleate in sufficiently lengthy simulations, although critical nucleation time for the latter is an order of magnitude higher than that for the former. We show that Cu64.5Zr35.5 is actually unstable to crystallization for large system sizes (N > 20 000). Both systems crystallize with the formation of tetrahedrally close packed Laves phases of different types. We argue that nucleation instability of the simulated Cu64.5Zr35.5 alloy is due to the fact that its composition is very close to that for the stable Cu2Zr compound with a C15 Laves phase structure. © 2018 Author(s).

The processes of particle nucleation and their evolution in a moving metastable layer of phase transition (supercooled liquid or supersaturated solution) are studied analytically. The transient integro-differential model for the density distribution function and metastability level is solved for the kinetic and diffusionally controlled regimes of crystal growth. The Weber–Volmer–Frenkel–Zel’dovich and Meirs mechanisms for nucleation kinetics are used. We demonstrate that the phase transition boundary lying between the mushy and pure liquid layers evolves with time according to the following power dynamic law: at + eZ1(t), where Z1(t) = ßt7/2 and Z1(t) = ßt2 in cases of kinetic and diffusionally controlled scenarios. The growth rate parameters a, ß and e are determined analytically. We show that the phase transition interface in the presence of crystal nucleation and evolution propagates slower than in the absence of their nucleation. This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’. © 2018 The Author(s) Published by the Royal Society. All rights reserved.

This article is concerned with a new analytical description of nucleation and growth of crystals in a metastable mushy layer (supercooled liquid or supersaturated solution) at the intermediate stage of phase transition. The model under consideration consisting of the non-stationary integro-differential system of governing equations for the distribution function and metastability level is analytically solved by means of the saddle-point technique for the Laplace-type integral in the case of arbitrary nucleation kinetics and time-dependent heat or mass sources in the balance equation. We demonstrate that the time-dependent distribution function approaches the stationary profile in course of time. This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’. © 2018 The Author(s) Published by the Royal Society. All rights reserved.

Understanding the physics of glass formation remains one of the major unsolved challenges of condensed matter science. As a material solidifies into a glass, it exhibits a spectacular slowdown of the dynamics upon cooling or compression, but at the same time undergoes only minute structural changes. Among the numerous theories put forward to rationalize this complex behavior, Mode-Coupling Theory (MCT) stands out as a unique framework that provides a fully first-principles-based description of glass phenomenology. This review outlines the key physical ingredients of MCT, its predictions, successes, and failures, as well as recent improvements of the theory. We also discuss the extension and application of MCT to the emerging field of non-equilibrium active soft matter.

When a liquid is cooled below its melting temperature under conditions that prevent it from crystallizing, it forms an amorphous solid, or "glass." Glass-forming materials are ubiquitous, ranging from familiar silica glasses of which everyday windows are composed, to liquid water. While structurally indistinguishable from high-temperature liquids, supercooled liquids exhibit rich and complex dynamics. For instance, as the temperature is lowered, structural reorganization within supercooled liquids occurs over increasingly long time scales. Inspecting atomistic mobility over an interval of time reveals that dynamics is "heterogeneous," with distinct regions of mobility and immobility in space-time. In this dissertation, we characterize glassy dynamics in experimental systems and in coarse-grained lattice models. We show how the characteristic dynamics of atomistic glass-forming materials can be reproduced using a kinetically constrained lattice model referred to as the Arrow model, and thus present glassy dynamics "on a lattice." We then show that combining the Arrow model with a second lattice model that undergoes a thermodynamic phase transition captures the competition between crystallization and glass formation experienced by a material cooled below its melting temperature. With this combined model, we demonstrate how specific cooling protocols influence polycrystalline structure, and we qualitatively reproduce the non-monotonic temperature dependence of crystallization time scales. Finally, we explore glassy dynamics "in nature" by applying many of the same tools and ideas used to characterize glasses to study dynamical features of protein side-chains. We demonstrate the presence of supercooled liquid-like dynamics in a biomolecular system.

When a liquid is cooled below its melting temperature under conditions that prevent it from crystallizing, it forms an amorphous solid, or "glass." Glass-forming materials are ubiquitous, ranging from familiar silica glasses of which everyday windows are composed, to liquid water. While structurally indistinguishable from high-temperature liquids, supercooled liquids exhibit rich and complex dynamics. For instance, as the temperature is lowered, structural reorganization within supercooled liquids occurs over increasingly long time scales. Inspecting atomistic mobility over an interval of time reveals that dynamics is "heterogeneous," with distinct regions of mobility and immobility in space-time. In this dissertation, we characterize glassy dynamics in experimental systems and in coarse-grained lattice models. We show how the characteristic dynamics of atomistic glass-forming materials can be reproduced using a kinetically constrained lattice model referred to as the Arrow model, and thus present glassy dynamics "on a lattice." We then show that combining the Arrow model with a second lattice model that undergoes a thermodynamic phase transition captures the competition between crystallization and glass formation experienced by a material cooled below its melting temperature. With this combined model, we demonstrate how specific cooling protocols influence polycrystalline structure, and we qualitatively reproduce the non-monotonic temperature dependence of crystallization time scales. Finally, we explore glassy dynamics "in nature" by applying many of the same tools and ideas used to characterize glasses to study dynamical features of protein side-chains. We demonstrate the presence of supercooled liquid-like dynamics in a biomolecular system.

The freezing of the cooperative reorientational motions in orientationally disordered (OD) molecular crystals marks the so-called \glassy" transition, which may be considered a lower-dimensional version of the structural glass transition. While structural glasses display both positional and orientational disorder, in fact, in orientational glasses the disorder involves exclusively the orientational degrees of freedom of the constituent molecules, while the molecular centres of mass form an ordered lattice. We report here on a glass-forming system with even less degrees of freedom, namely the OD phase of a dipolar benzene derivative, pentachloronitrobenzene (C6Cl5NO2). We probe the orientational dynamics of PCNB as a function of temperature and pressure by means of dielectric spectroscopy at normal and high pressure and high-pressure density measurements, and show that the system exhibits a double primary relaxation feature associated with two distinct motions of the molecular dipole moment. After ruling out an interpretation in terms of primitive or intramolecular relaxations, we discuss an assignment of the double relaxation feature based on the material's anisotropy and on the comparison with discotic liquid crystals., Peer Reviewed, Postprint (published version)

We present a full characterization of the orientationally disordered cocrystal of C-60 with (1,1,2)-triChloroethane (C2H3Cl3), by means of X-ray diffraction, Raman spectroscopy, and broadband dielectric spectroscopy. Our results include the determination of molecular con formations, lattice structure, positional disorder, and, molecular reorientational dynamics down to the microsecond time scale. We find that, while in the disordered solid phase of pure C2H3Cl3 the molecules exist only in the gauche conformation, both gauche and transoid conformers are present in the solvate, where they occupy the largest interstitial cavities between the fullerene species. The two C2H3Cl3 conformers exhibit separate, independent relaxations, exhibiting simply activated behavior in the measured temperature range. The relaxation, of the transoid conformer, which has twice the dipole moment of the gmiehe isomer, is significantly slower than that of the latter, due to the high polarizability of C-60 resulting in an electrostatic drag against the reorientations of the dipolar C2H3O3 species. The observation of two distinct, simply activated relaxations freezing at distinct temperatures indicates:that they are not truly many-body relaxations, which may be rationalized considering:that the C2H3Cl3 molecules are separated by the relatively bulky C-60 spacers., Peer Reviewed, Postprint (published version)

The polymorphism and the dynamics of a simple rigid molecule (1-fluoro-adamantane) have been studied by means of X-ray powder diffraction and broadband dielectric spectroscopy. At temperatures below the melting point, the molecule forms an orientationally disordered Phase I with a cubic-centered structure (Phase I, Fm (3) over barm, Z = 4). This phase possesses eight equilibrium positions for the fluorine atom, with equal occupancy factors of 1/8. A solid-solid phase transition to a low-temperature tetragonal phase (Phase II, P (4) over bar2(1)c, Z = 2) reduces the statistical disorder to only four possible equivalent sites for the fluorine atom, with fractional occupancies of 1/4. The dynamics has been rationalized under the constraints imposed by the space group of the crystal structure determined by powder X-ray diffraction. The dielectric spectroscopy study reveals that the statistical disorder in Phase II is dynamic in character and is associated with reorientational jumps along the two-and three-fold axes. In the dielectric loss spectra, the cooperative (alpha) relaxation exhibits a shoulder on the high-frequency side. This remarkable finding clearly reveals the existence of two intrinsic reorientational processes associated with the exchange of the F atom along the four sites. In addition to such, Peer Reviewed, Postprint (published version)

The dielectric and mechanical spectroscopies of acetate of cis- and trans-2-phenyl-5-hydroxymethyl-1,3- dioxane are reported in the frequency domain from 10−2 to 106 Hz. This ester has been selected in this study for its predominant á relaxation with regard to the â relaxation, which can be neglected. This study consists of determining an interconversion algorithm between dielectric and mechanical measurements, given by using a relation between rotational and translational complex viscosities. These important viscosities were obtained from measures of the dielectric complex permittivity and by dynamic mechanical analysis, respectively. The definitions of rotational and translational viscosities were evaluated by means of fractional calculus, by using the fit parameters of theHavriliak-Negami empirical model obtained in the dielectric and mechanical characterization of the á relaxation. This interconversion algorithm is a generalization of the break of the Stokes-Einstein-Debye relationship. It uses a power law with an exponent defined as the shape factor, which modifies the translational viscosity. Two others factors are introduced for the interconversion, a shift factor, which displaces the translational viscosity in the frequency domain, and a scale factor, which makes equal values of the two viscosities. In this paper, the shape factor has been identified as the relation between the slopes of the moduli of the complex viscosities at higher frequency. This is interpreted as the degree of kinetic coupling between the molecular rotation and translational movements. Alternatively, another interconversion algorithm has been expressed by means of dielectric and mechanical moduli.

The crystal nucleation of salicylic acid was explored in a range of solvents using induction time and metastable zone width measurements. In total 3100 experiments were performed to collect statistically valid nucleation results. The lognormal cumulative probability function provided a representative fit for both induction time and metastable zone width distributions. At equal driving force the induction time is found to increase in the order chloroform, ethyl acetate, acetonitrile, acetone, methanol and acetic acid, and this order agrees with the order of increasing interfacial energy The metastable zone width (MSZW) value (expressed as supersaturation driving force) was highest in acetic acid followed by a lower value in methanol, consistent with the induction time results. In ethyl acetate, acetonitrile and acetone the corresponding MSZW values were lower but the order among these three solvents varied depending on the cooling rate and saturation temperature. A novel format for comparing the induction time and MSZW experiments is presented. The analysis reveals that the time of nucleation in the metastable zone width experiments is also dependent on the time of transforming clusters into nuclei, and not only governed by the rate of supersaturation generation. The relative influence of this transformation time depends on the solvent and the cooling rate.

The dielectric and mechanical spectroscopies of acetate of cis- and trans-2-phenyl-5-hydroxymethyl-1,3- dioxane are reported in the frequency domain from 10−2 to 106 Hz. This ester has been selected in this study for its predominant á relaxation with regard to the â relaxation, which can be neglected. This study consists of determining an interconversion algorithm between dielectric and mechanical measurements, given by using a relation between rotational and translational complex viscosities. These important viscosities were obtained from measures of the dielectric complex permittivity and by dynamic mechanical analysis, respectively. The definitions of rotational and translational viscosities were evaluated by means of fractional calculus, by using the fit parameters of theHavriliak-Negami empirical model obtained in the dielectric and mechanical characterization of the á relaxation. This interconversion algorithm is a generalization of the break of the Stokes-Einstein-Debye relationship. It uses a power law with an exponent defined as the shape factor, which modifies the translational viscosity. Two others factors are introduced for the interconversion, a shift factor, which displaces the translational viscosity in the frequency domain, and a scale factor, which makes equal values of the two viscosities. In this paper, the shape factor has been identified as the relation between the slopes of the moduli of the complex viscosities at higher frequency. This is interpreted as the degree of kinetic coupling between the molecular rotation and translational movements. Alternatively, another interconversion algorithm has been expressed by means of dielectric and mechanical moduli.

Poly(vinylpyrrolidone-co-butyl acrylate) samples with different proportions of monomers were prepared as tractable and hydrophilic materials. An analysis of the intermolecular interactions between the polymer groups was carried out by FTIR The dependence of the C=O bands (lactam and pendant butyl ester) with the composition suggests a strong interaction between the lactam groups. They exert an important influence in the molecular mobility, which was studied by DSC and DRS. A single narrow glass transition temperature (T-g) is observed in each random copolymer, consistent with a single phase of low compositional nanoheterogeneity. The dependence of the T-g with the composition suggests significant interactions between polymer components. The dielectric spectra show gamma, beta, and alpha relaxations in increasing order of temperature, followed by conductive contributions. The apparent activation energies for secondary relaxations have similar values for all the samples. The gamma-process is related to the local motions of the butyl units and the beta-process is a Johari-Golstein secondary relaxation that is related to the local motions of the pyrrolidone group together with the motion of polymer backbone segments.

Poly(vinylpyrrolidone-co-butyl acrylate) samples with different proportions of monomers were prepared as tractable and hydrophilic materials. An analysis of the intermolecular interactions between the polymer groups was carried out by FTIR The dependence of the C=O bands (lactam and pendant butyl ester) with the composition suggests a strong interaction between the lactam groups. They exert an important influence in the molecular mobility, which was studied by DSC and DRS. A single narrow glass transition temperature (T-g) is observed in each random copolymer, consistent with a single phase of low compositional nanoheterogeneity. The dependence of the T-g with the composition suggests significant interactions between polymer components. The dielectric spectra show gamma, beta, and alpha relaxations in increasing order of temperature, followed by conductive contributions. The apparent activation energies for secondary relaxations have similar values for all the samples. The gamma-process is related to the local motions of the butyl units and the beta-process is a Johari-Golstein secondary relaxation that is related to the local motions of the pyrrolidone group together with the motion of polymer backbone segments.

When a liquid is supercooled towards the glass transition, its dynamics drastically slows down, whereas its static structure remains relatively unchanged. Finding a structural signature of the dynamic slowing down is a major challenge, yet it is often too subtle to be uncovered. Here we discover the structural signatures for both translational and rotational dynamics in monolayers of colloidal ellipsoids by video microscopy experiments and computer simulations. The correlation lengths of the dynamic slowest-moving clusters, the static glassy clusters, the static local structural entropy and the dynamic heterogeneity follow the same power-law divergence, suggesting that the kinetic slowing down is caused by a decrease in the structural entropy and an increase in the size of the glassy cluster. Ellipsoids with different aspect ratios exhibit single-or double-step glass transitions with distinct dynamic heterogeneities. These findings demonstrate that the particle shape anisotropy has important effects on the structure and dynamics of the glass.

Activity and activity coefficients of lanthanum were determined for the first time in gallium-indium eutectic based alloys in a wide temperature range employing electromotive force method. Activity of β-La and super cooled liquid lanthanum in Ga-In eutectic based alloys between 573 and 1073 K linearly depends on the reciprocal temperature: lgaβ-La(Ga-In)=5.660-15, 352T±0.093 lgaLa(Ga-In)=6.074-15,839T±0.093 Activity coefficients of β-La and super cooled liquid lanthanum in this system at 617-1073 K are described by the following equations: lgγβ-La (Ga-In)=3.786-12,216T±0.171 lgγLa(Ga-In)=4. 199-12,703T±0.171 In addition activity of lanthanum in alloys with In was also determined in the same temperature range. © 2012 Elsevier B.V. All rights reserved.

4403, open, Phase change materials based on chalcogenide alloys are attracting an increasing interest worldwide due to their ability to undergo reversible and fast transitions between the amorphous and crystalline phases upon heating. This property is exploited in rewritable optical media (CD, DVD, Blu-Ray Discs) and electronic nonvolatile memories of new concept, the Phase Change Memories (PCM). The strong optical and electronic contrast between the crystal and the amorphous allows discriminating between the two phases that correspond to the two bits of binary information zero and one. The material of choice for applications is the ternary compound Ge2Sb2Te5 (GST). However, the related binary alloy GeTe has also been thoroughly investigated because of its higher crystallization temperature and better data retention at high temperature with respect to GST. PCM devices, born thanks to the work of Ovshinsky in the late 1960s, offer extremely fast programming, extended cycling endurance, good reliability and inexpensive, easy integration. A PCM is essentially a resistor of a thin film of the chalcogenide alloy with a low field resistance that changes by several orders of magnitude across the phase change. In memory operations, cell read out is performed at low bias. Programming the memory requires instead a relatively large current to heat up the chalcogenide and induce the phase change, either the melting of the crystal and subsequent amorphization (RESET) or the recrystallization of the amorphous (SET). In the last few years, atomistic simulations based on density functional theory (DFT) have provided useful insights into the properties of phase change materials. However, several key issues such as the thermal conductivity at the nanoscale or the origin of the fast crystallization, just to name a few, are presently beyond the reach of ab initio simulations due to the high computational cost. In fact, first principles simulations can deal at most with 10^2 atoms on the timescale, open, Sosso, Sosso, G

We study the rotational dynamics of a supercooled molecular liquid by means of molecular dynamics simulations. The system under investigation is composed of rigid diatomic molecules with an associate dipole moment. At room temperature, orientational correlations decrease rapidly with increasing distances. Upon cooling, angles between dipole moments of molecules within the first coordination shell decrease. As for the dynamical properties, rotational diffusion coefficients decrease with temperature at a smaller rate than translational diffusion coefficients do, and the critical temperature associated with the former is lower than the one corresponding to their translational counterparts. Translation and rotation about an inertial axis are uncorrelated, whereas some coupling between translation and dipole reorientation is obtained., Postprint (published version)

Under cooling, a liquid can undergo a transition to the glassy state either as a result of a continuous slowing down or by a first-order polyamorphous phase transition. The second scenario has so far always been observed in a metastable liquid domain below the melting point where crystalline nucleation interfered with the glass formation. We report the first observation of the liquid-glass transition by a first-order polyamorphous phase transition from the equilibrium stable liquid phase. The observation was made in a molecular dynamics simulation of a one-component system with a model metallic pair potential. In this way, the model, demonstrating the thermodynamic glass transition from a stable liquid phase, may be regarded as a candidate for a simple monatomic ideal glass former. This observation is of conceptual importance in the context of continuing attempts to resolve the long-standing Kauzmann paradox. The possibility of a thermodynamic glass transition from an equilibrium melt in a metallic system also indicates a new strategy for the development of bulk metallic glass-forming alloys., QC 20101210

Ti-based metallic glasses (MGs) due to their relative low densities exhibit ultrahigh specific characteristics. In this article the glass-forming behavior and atomic structure of Ti50Cu50 MG were investigated through molecular dynamics simulation (MDS) using the general embedded-atom method (GEAM) potential. As observed experimentally, simulated Ti 50Cu50 alloy undergoes three states on quenching: (i) equilibrium liquid; (ii) supercooled liquid and (iii) glassy solid. The atomic configuration of the glass was analysed based on the radial distribution function (RDF) and Voronoi tessellation (VT). It was found that there exist a variety of polyhedral units in Ti50Cu50 MG, where distorted icosohedral and bcc clusters are dominant. © (2010) Trans Tech Publications., Sponsors: The Minerals, Metals and Materials Society (TMS)

The understanding of complex condensed matter systems is an area of intense study. In this thesis, some properties of simple liquids with strong preference for tetrahedral local ordering are explored. These liquids are amenable to supercooling, and give complex crystalline structures on eventual crystallisation. All liquids studied are simple, monatomic and are similar to real metallic liquids. The vibrational density of states of a glass created in simulation is calculated. We show a correspondence between the vibrational properties of the crystal and the glass, indicating that the vibrational spectra of crystals can be used to understand the more complex vibrational spectra of the glass of the same substance. The dynamics of supercooled liquids is investigated using a previously not implemented comprehensive measure of structural relaxation. This new measure decays more slowly in the deeply supercooled domain than the commonly used measure. A new atomic model for octagonal quasicrystals is presented. The model is based on findings from a molecular dynamics simulation that resulted in 45˚ twinned β-Mn. A decoration is derived from the β-Mn unit cell and the unit cell of the intermediate structure found at the twinning interface. Extensive simulations are used to explore the phase diagram of a liquid at low densities. The resulting phase diagram shows a spinodal line and a phase coexistence region between a liquid and a crystalline phase ending in a critical point. This contradicts the old conclusion of the Landau theory -- that continuous transitions between liquids and crystals cannot exist The same liquid is explored at higher densities. Upon cooling the liquid performs a first order liquid-liquid phase transition. The low temperature liquid is shown to be strong and to have very good glass forming abilities. This result offers new insights into fragile to strong transitions and suggests the possibility of a good metallic glass former., At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: In progress.

We study low-temperature properties of the XY spin model on a negatively curved surface. Geometric curvature of the surface gives rise to frustration in local spin configuration, which results in the formation of high-energy spin clusters scattered over the system. Asymptotic behavior of the spin-glass susceptibility suggests a zero-temperature glass transition, which is attributed to multiple optimal configurations of spin clusters due to nonzero surface curvature of the system. It implies that a constant ferromagnetic spin interaction on a regular lattice can exhibit glasslike behavior without possessing any disorder if the lattice is put on top of a negatively curved space such as a hyperbolic surface., QC 20110412

The understanding of complex condensed matter systems is an area of intense study. In this thesis, some properties of simple liquids with strong preference for tetrahedral local ordering are explored. These liquids are amenable to supercooling, and give complex crystalline structures on eventual crystallisation. All liquids studied are simple, monatomic and are similar to real metallic liquids. The vibrational density of states of a glass created in simulation is calculated. We show a correspondence between the vibrational properties of the crystal and the glass, indicating that the vibrational spectra of crystals can be used to understand the more complex vibrational spectra of the glass of the same substance. The dynamics of supercooled liquids is investigated using a previously not implemented comprehensive measure of structural relaxation. This new measure decays more slowly in the deeply supercooled domain than the commonly used measure. A new atomic model for octagonal quasicrystals is presented. The model is based on findings from a molecular dynamics simulation that resulted in 45˚ twinned β-Mn. A decoration is derived from the β-Mn unit cell and the unit cell of the intermediate structure found at the twinning interface. Extensive simulations are used to explore the phase diagram of a liquid at low densities. The resulting phase diagram shows a spinodal line and a phase coexistence region between a liquid and a crystalline phase ending in a critical point. This contradicts the old conclusion of the Landau theory -- that continuous transitions between liquids and crystals cannot exist The same liquid is explored at higher densities. Upon cooling the liquid performs a first order liquid-liquid phase transition. The low temperature liquid is shown to be strong and to have very good glass forming abilities. This result offers new insights into fragile to strong transitions and suggests the possibility of a good metallic glass former., At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: In progress.

The understanding of complex condensed matter systems is an area of intense study. In this thesis, some properties of simple liquids with strong preference for tetrahedral local ordering are explored. These liquids are amenable to supercooling, and give complex crystalline structures on eventual crystallisation. All liquids studied are simple, monatomic and are similar to real metallic liquids. The vibrational density of states of a glass created in simulation is calculated. We show a correspondence between the vibrational properties of the crystal and the glass, indicating that the vibrational spectra of crystals can be used to understand the more complex vibrational spectra of the glass of the same substance. The dynamics of supercooled liquids is investigated using a previously not implemented comprehensive measure of structural relaxation. This new measure decays more slowly in the deeply supercooled domain than the commonly used measure. A new atomic model for octagonal quasicrystals is presented. The model is based on findings from a molecular dynamics simulation that resulted in 45˚ twinned β-Mn. A decoration is derived from the β-Mn unit cell and the unit cell of the intermediate structure found at the twinning interface. Extensive simulations are used to explore the phase diagram of a liquid at low densities. The resulting phase diagram shows a spinodal line and a phase coexistence region between a liquid and a crystalline phase ending in a critical point. This contradicts the old conclusion of the Landau theory -- that continuous transitions between liquids and crystals cannot exist The same liquid is explored at higher densities. Upon cooling the liquid performs a first order liquid-liquid phase transition. The low temperature liquid is shown to be strong and to have very good glass forming abilities. This result offers new insights into fragile to strong transitions and suggests the possibility of a good metallic glass former., At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: In progress.

Uniaxial compression tests of Mg54Cu28Ag7Y11 metallic glass were performed in the supercooled liquid region (468 K) at a strain rate range of 5x10(exp-4) - 2x10(exp -4) s(exp-1). In the course of testing, shear thickening behavior was observed. The deformation behavior of the glassy metal is discussed with special emphasis on the stress overshoot commonly reported in the metallic glass literature, relaxation behavior, and the previously unreported shear thickening behavior observed. Two potential mechanisms are presented to explain the deformation behavior of the glassy metal., The original document contains color images. All DTIC reproductions will be in black and white. Submitted for publication to Scripta Materialia.

We recapitulate and generalize the concept of the freezing-melting hysteresis that attributes this phenomenon to a free-energy barrier between metastable and stable states of pore-filling material. In a phenomenological description, we show that under commonly encountered conditions, this renders the freezing-point depression Delta T-f defined by the surface-to-volume ratio S/V, whereas the melting-point depression Delta T-m by the mean curvature kappa of the pore surface, with Delta T-m/Delta T-f=2 kappa(V/S). Employing H-1 NMR cryoporometry, we experimentally demonstrate the linear correlation between Delta T-m and Delta T-f for several liquids with different Delta T-f,T-m imbibed in controlled pore glasses. The results compare favorably to the morphological properties of the glasses determined by other techniques. Our findings suggest a simple method for analyzing the pore morphology from the observed phase transition temperatures., QC 20100525

Pressure effects on glass transition temperature and supercooled liquid region of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass have been investigated by performing in situ high-temperature and high-pressure x-ray powder diffraction measurements using synchrotron radiation. The glass transition was detected from the change of the slope of peak position as a function of temperature. It is found that the glass transition temperature increases with pressure by 4.4 K/GPa for the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass, and the supercooled liquid range decreases with pressure by 2.9 K/GPa in a pressure range of 0-2.2 GPa. This method opens a possibility to study the pressure effect of glass transition process in glassy systems under high pressures (>1 GPa). (C) 2004 American Institute of Physics.

Pressure effects on glass transition temperature and supercooled liquid region of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass have been investigated by performing in situ high-temperature and high-pressure x-ray powder diffraction measurements using synchrotron radiation. The glass transition was detected from the change of the slope of peak position as a function of temperature. It is found that the glass transition temperature increases with pressure by 4.4 K/GPa for the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass, and the supercooled liquid range decreases with pressure by 2.9 K/GPa in a pressure range of 0-2.2 GPa. This method opens a possibility to study the pressure effect of glass transition process in glassy systems under high pressures (>1 GPa). (C) 2004 American Institute of Physics.

Pressure effects on glass transition temperature and supercooled liquid region of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass have been investigated by performing in situ high-temperature and high-pressure x-ray powder diffraction measurements using synchrotron radiation. The glass transition was detected from the change of the slope of peak position as a function of temperature. It is found that the glass transition temperature increases with pressure by 4.4 K/GPa for the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass, and the supercooled liquid range decreases with pressure by 2.9 K/GPa in a pressure range of 0-2.2 GPa. This method opens a possibility to study the pressure effect of glass transition process in glassy systems under high pressures (>1 GPa). (C) 2004 American Institute of Physics.

This document presents the results of an investigation of remote sensing technologies applicable to the problem of aircraft icing potential detection. The long-term goal is to develop an aircraft mounted sensor capable of detecting dangerous levels of supercooled liquid water tens of kilometers ahead of the aircraft. Clouds with supercooled liquid water exhibit a potential for icing that is a function of water content, and to some degree, the range of droplet diameters 14 CFR Part 25 Appendix C. Appendix C conditions are dangerous to aircraft without ice protection; however, they are not dangerous to most aircraft with ice protection. Instruments capable of mapping cloud liquid water content and mean particle size were investigated. Furthermore, instruments capable of probing air temperature were also investigated, in as much as they may provide a means of detecting regions of warmer air where drops are not supercooled.

Kinetically constrained models (KCMs) are able to account for many of the slow dynamical properties of glass forming systems such as dynamic heterogeneity and Stokes-Einstein breakdown using simple models with simple dynamical rules. In this thesis we study several KCMs and extend them to include fast degrees of freedom. We show how the method of Monte Carlo with absorbing Markov chains can be applied to a particular class of KCMs, the facilitated spin models, to create an efficient numerical algorithm that can speed up simulations by several orders of magnitude. Another branch of KCMs, the constrained lattice gases, are studied and new results for a version on an FCC lattice in three dimensions are presented. This model is necessary when fast dynamics are studied and dimension plays an important role. To establish how fast degrees of freedom can be introduced without changing the character of the underlying KCMs we introduce coupled Ising spins to several existing models. We find that these models can reproduce much of the fast behaviour seen in the beta-relaxation of real supercooled liquids without changing the slow behaviour that is already well described by KCMs. Lastly, by considering harmonic interactions between particles we study the relation between short-time vibrational modes and long-time relaxational dynamics in two constrained lattice gas models. We find an excess in the vibrational density of states similar to the "Boson peak" of glasses and we find a correlation between the location of these low (high) frequency vibrational modes and regions of high (low) propensity for motion in agreement with recent results from atomistic simulations.