Showing papers on "Phase transition published in 2001"
Book•
01 Apr 2001TL;DR: In this paper, the mapping to classical statistical mechanics: single site models 3. Quantum Ising and Rotor Models: 4. The Ising chain in a transverse field 5. Quantum rotor models: large N limit 6. The d = 1, 0 (N greater than or equal to 3) rotor models 7. Quantum spin chains: bosonization 14. Magnetic ordering transitions of disordered systems 16.
Abstract: Part I. Introduction: 1. Basic concepts 2. The mapping to classical statistical mechanics: single site models 3. Overview Part II. Quantum Ising and Rotor Models: 4. The Ising chain in a transverse field 5. Quantum rotor models: large N limit 6. The d = 1, 0 (N greater than or equal to 3) rotor models 7. The d = 2 (N greater than or equal to 3) rotor models 8. Physics close to and above the upper-critical dimension 9. Transport in d = 2 Part III. Other Models: 10. Boston Hubbard model 11. Dilute Fermi and Bose gases 12. Phase transitions of Fermi liquids 13. Heisenberg spins: ferromagnets and antiferromagnets 14. Spin chains: bosonization 15. Magnetic ordering transitions of disordered systems 16. Quantum spin glasses.
1,870 citations
TL;DR: Femtosecond x-ray and visible pulses were used to probe structural and electronic dynamics during an optically driven, solid-solid phase transition in VO, suggesting that, in this regime, the structural transition may not be thermally initiated.
Abstract: Femtosecond x-ray and visible pulses were used to probe structural and electronic dynamics during an optically driven, solid-solid phase transition in VO(2). For high interband electronic excitation (approximately 5 x 10(21) cm(-3)), a subpicosecond transformation into the high-T, rutile phase of the material is observed, simultaneous with an insulator-to-metal transition. The fast time scale observed suggests that, in this regime, the structural transition may not be thermally initiated.
1,101 citations
TL;DR: The results support the concept of a jamming phase diagram for attractive colloidal particles, providing a unifying link between the glass transition, gelation and aggregation.
Abstract: A wide variety of systems, including granular media, colloidal suspensions and molecular systems, exhibit non-equilibrium transitions from a fluid-like to a solid-like state, characterized solely by the sudden arrest of their dynamics. Crowding or jamming of the constituent particles traps them kinetically, precluding further exploration of the phase space1. The disordered fluid-like structure remains essentially unchanged at the transition. The jammed solid can be refluidized by thermalization, through temperature or vibration, or by an applied stress. The generality of the jamming transition led to the proposal2 of a unifying description, based on a jamming phase diagram. It was further postulated that attractive interactions might have the same effect in jamming the system as a confining pressure, and thus could be incorporated into the generalized description. Here we study experimentally the fluid-to-solid transition of weakly attractive colloidal particles, which undergo markedly similar gelation behaviour with increasing concentration and decreasing thermalization or stress. Our results support the concept of a jamming phase diagram for attractive colloidal particles, providing a unifying link between the glass transition3, gelation4,5 and aggregation6,7,8.
827 citations
TL;DR: In this article, a morphotropic phase boundary (MPB) piezoelectric with ferroelectric phase transition (Tc) exceeding that of PbZrO3-PbTiO3 (PZT) was investigated.
Abstract: New morphotropic phase boundary (MPB) piezoelectrics, with ferroelectric phase transition (Tc) exceeding that of PbZrO3–PbTiO3 (PZT), were investigated. Based on a perovskite tolerance factor-Tc relationship, new high Tc MPB systems were projected in the Bi(Me)O3–PbTiO3 system, where Me is a relatively large B+3-site cation. For the (1-x)BiScO3–(x)PbTiO3 solid solution, a MPB was found at x-0.64 separating the rhombohedral and tetragonal phases, with correspondingly enhanced dielectric and piezoelectric properties. A transition temperature Tc of ~ 450°C was determined with evidence of Tc's on the order of ≥ 600°C in the BiInO3 and BiYbO3 analogues, though issues of perovskite stability remain for the smaller tolerance end-member systems.
769 citations
TL;DR: In this paper, a free-standing anisotropic side chain liquid crystalline elastomer films have been prepared using mesogens with laterally affixed polymerizable side chains and the calculated cross-linking density, as determined from the Young's modulus, was in the 10 -5 mol/cm3 range.
Abstract: Free-standing anisotropic side chain liquid crystalline elastomer films have been prepared using mesogens with laterally affixed polymerizable side chains. We present data on two networks: one containing the monomer of 4‘-acryloyloxybutyl 2,5-(4‘-butyloxybenzoyloxy)benzoate and another from a 50/50 mol % mixture of the above with 4‘-acryloyloxybutyl 2,5-di(4‘-pentylcyclohexyloyloxy)benzoate. The cross-linking was achieved using 10 mol % of 1,6-hexanediol diacrylate. The calculated cross-linking density, as determined from the Young's modulus, was in the 10 -5 mol/cm3 range. Thermoelastic responses show strain changes through the nematic−isotropic phase transition to be 30−45%. The order parameters of the oriented films were determined from the dichroic ratio of IR absorption at 3343 cm-1 to the in-plane aromatic stretching overtone of the LC mesogen core. The variation of the order parameter with temperature scales similar to the strain changes at constant stress. Isostrain studies, conducted through the...
600 citations
TL;DR: An approximate solution at the critical point of the spherical to axially deformed shape phase transition in nuclei is presented.
Abstract: An approximate solution at the critical point of the spherical to axially deformed shape phase transition in nuclei is presented. The eigenvalues of the Hamiltonian are expressed in terms of zeros of Bessel functions of irrational order.
585 citations
TL;DR: In this paper, it was shown that the 6th-order Devonshire theory cannot support a monoclinic phase, and an extension of the theory to higher orders was proposed.
Abstract: Devonshire theory provides a successful phenomenological description of many cubic perovskite ferroelectrics such as ${\mathrm{BaTiO}}_{3}$ via a sixth-order expansion of the free energy in the polar order parameter. However, the recent discovery of a novel monoclinic ferroelectric phase in the PZT system by Noheda et al. [Appl. Phys. Lett. 74, 2059 (1999)] poses a challenge to this theory. Here, we confirm that the sixth-order Devonshire theory cannot support a monoclinic phase, and consider extensions of the theory to higher orders. We show that an eighth-order theory allows for three kinds of equilibrium phases in which the polarization is confined not to a symmetry axis but to a symmetry plane. One of these phases provides a natural description of the newly observed monoclinic phase. Moreover, the theory makes testable predictions about the nature of the phase boundaries between monoclinic, tetragonal, and rhombohedral phases. A ferroelectric phase of the lowest (triclinic) symmetry type, in which the polarization is not constrained by symmetry, does not emerge until the Devonshire theory is carried to twelfth order. A topological analysis of the critical points of the free-energy surface facilitates the discussion of the phase transition sequences.
575 citations
TL;DR: In this paper, the formation of topologically close-packed (TCP) phases due to the addition of solid solution strengtheners, such as rhenium, molybdenum and tungsten, has been studied.
510 citations
TL;DR: In this article, the charged Schwarzschild-Anti-deSitter (SAdS) thermodynamics in 5d Einstein-Gauss-Bonnet gravity with electromagnetic field was investigated.
Abstract: We investigate the charged Schwarzschild-Anti-deSitter (SAdS) BH thermodynamics in 5d Einstein-Gauss-Bonnet gravity with electromagnetic field. The Hawking-Page phase transitions between SAdS BH and pure AdS space are studied. The corresponding phase diagrams (with critical line defined by GB term coefficient and electric charge) are drawn. The possibility to account for higher derivative Maxwell terms is mentioned.
In frames of proposed dS/CFT correspondence it is demonstrated that brane gravity maybe localized similarly to AdS/CFT.
SdS BH thermodynamics in 5d Einstein and Einstein-Gauss-Bonnet gravity is considered. The corresponding (complicated) surface counterterms are found and used to get the conserved BH mass, free energy and entropy. The interesting feature of of higher derivative gravity is the possibility for negative (or zero) SdS (or SAdS) BH entropy which depends on the parameters of higher derivative terms. We speculate that the appearence of negative entropy may indicate a new type instability where a transition between SdS (SAdS) BH with negative entropy to SAdS (SdS) BH with positive entropy would occur.
479 citations
TL;DR: The presence of a LDL and a HDL can be directly related to an interaction potential with an attractive part and two characteristic short-range repulsive distances, and the results show that the LDL and HDL phases can occur in systems with no density anomaly.
Abstract: Recent experimental results indicate that phosphorus--a single-component system--can have a high-density liquid (HDL) and a low-density liquid (LDL) phase A first-order transition between two liquids of different densities is consistent with experimental data for a variety of materials, including single-component systems such as water, silica and carbon Molecular dynamics simulations of very specific models for supercooled water, liquid carbon and supercooled silica predict a LDL-HDL critical point, but a coherent and general interpretation of the LDL-HDL transition is lacking Here we show that the presence of a LDL and a HDL can be directly related to an interaction potential with an attractive part and two characteristic short-range repulsive distances This kind of interaction is common to other single-component materials in the liquid state (in particular, liquid metals), and such potentials are often used to describe systems that exhibit a density anomaly However, our results show that the LDL and HDL phases can occur in systems with no density anomaly Our results therefore present an experimental challenge to uncover a liquid-liquid transition in systems like liquid metals, regardless of the presence of a density anomaly
364 citations
TL;DR: The results reveal a change in the energy landscape with decreasing temperature, which underlies a transition from a fragile liquid at high temperature to a strong liquid at low temperature, and it is suggested that a specific heat anomaly is associated with this fragile-to-strong transition.
Abstract: Liquid silica is the archetypal glass former, and compounds based on silica are ubiquitous as natural and man-made amorphous materials. Liquid silica is also the extreme case of a 'strong' liquid, in that the variation of viscosity with temperature closely follows the Arrhenius law as the liquid is cooled toward its glass transition temperature. In contrast, most liquids are to some degree 'fragile', showing significantly faster increases in their viscosity as the glass transition temperature is approached. Recent studies have demonstrated the controlling influence of the potential energy hypersurface (or 'energy landscape') of the liquid on the transport properties near the glass transition. But the origin of strong liquid behaviour in terms of the energy landscape has not yet been resolved. Here we study the static and dynamic properties of liquid silica over a wide range of temperature and density using computer simulations. The results reveal a change in the energy landscape with decreasing temperature, which underlies a transition from a fragile liquid at high temperature to a strong liquid at low temperature. We also show that a specific heat anomaly is associated with this fragile-to-strong transition, and suggest that this anomaly is related to the polyamorphic behaviour of amorphous solid silica.
Book•
01 Oct 2001
TL;DR: Theoretical theories of phase transitions in crystalline solids have been studied in this paper, including homogeneous second phase precipitation transformations involving interfacial diffusion diffusionless transformations spinodal decomposition high pressure phase transformations atomic ordering solidification.
Abstract: Thermodynamics and phase diagrams of materials diffusion in crystalline solids statistical theories of phase transitions homogeneous second phase precipitation transformations involving interfacial diffusion diffusionless transformations spinodal decomposition high pressure phase transformations atomic ordering solidification.
TL;DR: For achievable experimental conditions, the transition to a superfluid phase is possible at the high critical temperature of about 0.5T(F).
Abstract: We consider the superfluid phase transition that arises when a Feshbach resonance pairing occurs in a dilute Fermi gas. We apply our theory to consider a specific resonance in potassium ( ${}^{40}\mathrm{K}$), and find that for achievable experimental conditions, the transition to a superfluid phase is possible at the high critical temperature of about ${0.5T}_{F}$. Observation of superfluidity in this regime would provide the opportunity to experimentally study the crossover from the superfluid phase of weakly coupled fermions to the Bose-Einstein condensation of strongly bound composite bosons.
TL;DR: Pressure-induced amorphization is observed on films of porous Si, which contains nanometre-sized domains of diamond-structured material, and it is found from Raman spectroscopy measurements that the high-density amorphous form obtained by this process transforms to low-densityAmorphous silicon upon decompression.
Abstract: Crystalline and amorphous forms of silicon are the principal materials used for solid-state electronics and photovoltaics technologies. Silicon is therefore a well-studied material, although new structures and properties are still being discovered. Compression of bulk silicon, which is tetrahedrally coordinated at atmospheric pressure, results in a transition to octahedrally coordinated metallic phases. In compressed nanocrystalline Si particles, the initial diamond structure persists to higher pressure than for bulk material, before transforming to high-density crystals. Here we report compression experiments on films of porous Si, which contains nanometre-sized domains of diamond-structured material. At pressures larger than 10 GPa we observed pressure-induced amorphization. Furthermore, we find from Raman spectroscopy measurements that the high-density amorphous form obtained by this process transforms to low-density amorphous silicon upon decompression. This amorphous-amorphous transition is remarkably similar to that reported previously for water, which suggests an underlying transition between a high-density and a low-density liquid phase in supercooled Si (refs 10, 14, 15). The Si melting temperature decreases with increasing pressure, and the crystalline semiconductor melts to a metallic liquid with average coordination approximately 5 (ref. 16).
TL;DR: The phase transition behavior of the BaTiO3-BaZrO3 system was studied using micro-Raman scattering and dielectric measurement techniques in this paper, where a single-phase perovskite structure was identified by the x-ray diffraction technique.
Abstract: In this study, the phase transition behavior of the BaTiO3–BaZrO3 system was studied using micro-Raman scattering and dielectric measurement techniques. BaZrxTi1−xO3 ceramics were prepared for x=0.00, 0.05, 0.08, 0.15, 0.20, and 1.00 compositions using a solid-state reaction technique. A single-phase perovskite structure of the ceramics was identified by the x-ray diffraction technique. The basic phase transition temperatures in these compositions were studied in the temperature range of 70–575 K. The tetragonal to cubic transition temperature was found to decrease with increasing Zr content. The orthorhombic to tetragonal transition temperature that increases with an initial increase in Zr content merges with the tetragonal–cubic transition for x⩾0.15 compositions. Raman spectra of rhombohedral and orthorhombic phases could not be distinguished. Excellent agreement between the crystallographic transition temperatures obtained by both techniques suggested that Zr substituted octahedra were uniformly distr...
TL;DR: In this article, a phase-field model for predicting the coherent microstructure evolution in constrained thin films is developed, which employs an analytical elastic solution derived for a constrained film with arbitrary eigenstrain distributions.
Abstract: A phase-field model for predicting the coherent microstructure evolution in constrained thin films is developed. It employs an analytical elastic solution derived for a constrained film with arbitrary eigenstrain distributions. The domain structure evolution during a cubic→tetragonal proper ferroelectric phase transition is studied. It is shown that the model is able to simultaneously predict the effects of substrate constraint and temperature on the volume fractions of domain variants, domain-wall orientations, domain shapes, and their temporal evolution.
Book•
20 Mar 2001
TL;DR: The micro-canonical thermodynamics of phase transitions studied in the Potts model liquid-gas transition and surface tension under constant pressure statistical fragmentation under repulsive forces of long range were studied in this article.
Abstract: The mechanical basis of thermodynamics micro-canonical thermodynamics of phase transitions studied in the Potts model liquid-gas transition and surface tension under constant pressure statistical fragmentation under repulsive forces of long range the collapse transition in self-gravitating systems first model-studies appendices - on the historical development of statistical nuclear multifragmentation models, the micro-canonical ensemble of Na-clusters, some general technical aspects of micro-canonical Monte Carlo simulation on a lattice.
01 Jan 2001
TL;DR: In this article, the random geometry of equilibrium phases is discussed and percolation techniques are used to obtain specific information about the phase diagram of the system, such as clusters, open paths, connectedness etc.
Abstract: Publisher Summary This chapter discusses the random geometry of equilibrium phases. Percolation will come into play here on various levels. Its concepts like clusters, open paths, connectedness etc. will be useful for describing certain geometric features of equilibrium phases, allowing characterizations of phases in percolation terms. Examples are presented where the (thermal) phase transition goes hand in hand with a phase transition in an associated percolation process. Percolation techniques can be used to obtain specific information about the phase diagram of the system. For example, equilibrium correlation functions are sometimes dominated by connectivity functions in an associated percolation problem which is easier to investigate. Further, representations in terms of percolation models yield explicit relations between certain observables in equilibrium models and some corresponding percolation quantities.
TL;DR: In this paper, a large magnetic entropy change was observed in Heusler alloy Ni52.6Mn23.1Ga24.3 single crystal near the martensitic structural transition temperature of 300 K with applied field along [001] direction.
Abstract: A large magnetic entropy change \DeltaS\ has been observed in Heusler alloy Ni52.6Mn23.1Ga24.3 single crystal near the martensitic structural transition temperature of 300 K with applied field along [001] direction. The obtained \DeltaS\ under an applied field of 5 T reaches 18.0 J/Kg K (corresponding 146 mJ/cm(3) K). A more important result is that \DeltaS\ can achieve constant increase of 4.0 J/Kg K for the field increase of every tesla. The very large magnetic entropy change is attributed to the abrupt change of magnetization when the first-order martensitic-austensitic structural transition takes place. The phenomena of the large magnetic entropy change and the easy adjustment of the martensitic-austensitic transition-temperature indicate that the non-rare-earth based Ni-Mn-Ga single-crystal materials may have potential applications as magnetic refrigerants.
TL;DR: In this article, solid solution LiCo 1-x Al x O 2 that has discretely higher Al concentration was formed at the surface up to ∼500 A inside the particle.
Abstract: Structural instability of LiCoO 2 can be improved by sol-gel coating of Al 2 O 3 and subsequent heat-treatments. While Al 2 O 3 phase does not exist after heat-treatments, solid solution LiCo 1-x Al x O 2 that has discretely higher Al concentration was formed at the surface up to ∼500 A inside the particle. However, heat-treatment to 700°C results in the presence of the solid solution beyond ∼500 A. The different Al concentration at the surface significantly affects the structural stability of the materials during cycling, and those prepared at 400°C do not show a phase transition from hexagonal to monoclinic phase. Disappearance of such a phase transition improves capacity retention of the cathode. Moreover, cathodes prepared at 400 and 500°C show improved layered characteristics with cation order.
TL;DR: The first application of pressure perturbation calorimetry (PPC) to determine the hydration properties of poly(N-isopropylacrylamide) (PNIPAM) in H2O and in D2O as the solutions undergo a temperature-induced phase transition was reported in this paper.
Abstract: We report the first application of pressure perturbation calorimetry (PPC) to determine the hydration properties of poly(N-isopropylacrylamide) (PNIPAM) in H2O and in D2O as the solutions undergo a temperature-induced phase transition. The technique, which measures the heat change resulting from a pressure change above a solution of PNIPAM placed in a microcalorimeter cell, yields the temperature dependence of the coefficient of thermal expansion, αp, of the polymer in solution and the change in volume of the solvation layer around the polymer chain. In the temperature ranges below and above the phase transition, αp of PNIPAM in H2O increased linearly with temperature. It underwent a sharp increase at the transition temperature, Tmax, then rapidly decreased. The phase transition was accompanied by an increase in the partial specific volume of the hydrated polymer. This increase was significantly higher for solutions of PNIPAM in D2O, compared to H2O. A study by PPC of the phase transition of hydrophobical...
TL;DR: In this paper, the Langevin dynamics for a simplified spherical version of this model were studied and the induced rotational symmetry of the spherical model reduced the dynamics in question to an N-dimensional coupled system of Ornstein-Uhlenbeck processes whose random drift parameters are the eigenvalues of certain random matrices.
Abstract: Sompolinski and Zippelius (1981) propose the study of dynamical systems whose invariant measures are the Gibbs measures for (hard to analyze) statistical physics models of interest. In the course of doing so, physicists often report of an “aging” phenomenon. For example, aging is expected to happen for the Sherrington-Kirkpatrick model, a disordered mean-field model with a very complex phase transition in equilibrium at low temperature. We shall study the Langevin dynamics for a simplified spherical version of this model. The induced rotational symmetry of the spherical model reduces the dynamics in question to an N-dimensional coupled system of Ornstein-Uhlenbeck processes whose random drift parameters are the eigenvalues of certain random matrices. We obtain the limiting dynamics for N approaching infinity and by analyzing its long time behavior, explain what is aging (mathematically speaking), what causes this phenomenon, and what is its relationship with the phase transition of the corresponding equilibrium invariant measures.
TL;DR: In this article, the swelling behavior of the colloidal particles as probed by dynamic light scattering (DLS) is discussed together with information on local structure and dynamics of the particles as obtained from small angle neutron scattering (SANS).
TL;DR: In this article, a model for an interface between the color-flavor-locked (CFL) phase and the nuclear phase is presented. But the model assumes that the mixed phase will occur only if the nuclear-CFL surface tension is significantly smaller than dimensional analysis would indicate.
Abstract: At nuclear matter density, electrically neutral strongly interacting matter in weak equilibrium is made of neutrons, protons, and electrons. At sufficiently high density, such matter is made of up, down, and strange quarks in the color-flavor-locked (CFL) phase, with no electrons. As a function of increasing density (or, perhaps, increasing depth in a compact star) other phases may intervene between these two phases, which are guaranteed to be present. The simplest possibility, however, is a single first order phase transition between CFL and nuclear matter. Such a transition, in space, could take place either through a mixed phase region or at a single sharp interface with electron-free CFL and electron-rich nuclear matter in stable contact. Here we construct a model for such an interface. It is characterized by a region of separated charge, similar to an inversion layer at a metal-insulator boundary. On the CFL side, the charged boundary layer is dominated by a condensate of negative kaons. We then consider the energetics of the mixed phase alternative. We find that the mixed phase will occur only if the nuclear-CFL surface tension is significantly smaller than dimensional analysis would indicate.
Book•
15 Jan 2001
TL;DR: In this paper, various experimental techniques used in the study of liquid crystals are described in detail and discussed in detail, including various experimental methods used for the analysis of liquid crystal lattice structures.
Abstract: This book describes in detail various experimental techniques used in the study of liquid crystals.[...]
TL;DR: Discontinuous reactions are solid state moving boundary phase transitions characterised by a discontinuous or abrupt change in orientation and composition between the matrix phases in the reactant and product aggregate across the migrating boundary or reaction front that provides a short circuit path of diffusion as discussed by the authors.
Abstract: Discontinuous reactions are solid state moving boundary phase transitions characterised by a discontinuous or abrupt change in orientation and composition between the matrix phases in the reactant and product aggregate across the migrating boundary or reaction front that provides a short circuit path of diffusion. The reactions include discontinuous precipitation, discontinuous coarsening, discontinuous dissolution, and diffusion induced grain boundary migration. All these reactions may account for a substantial change in microstructure, composition, and material properties, and hence, deserve adequate scientific attention for a better understanding. The present review provides a comprehensive discussion on the current status of understanding about nucleation and growth mechanisms, genesis and driving force, product morphology and distribution, kinetic growth models, and related experimental techniques, and above all, the unresolved questions concerning these discontinuous reactions. In addition, ...
01 Jan 2001
TL;DR: In this article, mean-field constraint theory, and numerical simulations of the vibrational density of state (floppy modes) in random and self-organized networks are used to analyze the measurements.
Abstract: We review Raman scattering, Mossbauer spectroscopy and T-modulated Differential Scanning Calorimetry experiments on several families of chalcogenide glasses. Mean-field constraint theory, and numerical simulations of the vibrational density of state (floppy modes) in random and self-organized networks are used to analyze the measurements. Our results provide evidence for three distinct phases of network glasses: floppy, intermediate and rigid, as a function of progressive cross-linking or mean coordination number ( r ). These phases are characterized by distinct elastic power-laws. The intermediate phase is characterized by a vanishing non-reversing heat-flow, ΔHnr ( r ) → 0, suggesting that glass compositions in this phase are configurationally close to their liquid counterparts, i.e. self-organized. The compositional width (and centroid) of the intermediate phase is found to be determined by glass structure. In random networks, the width of the intermediate phase almost vanishes, and a solitary floppy to rigid phase transition is observed, in excellent accord with extended constraint theory. In the chalcogenides, some degree of self-organization invariably occurs and opens an intermediate phase between the floppy and rigid phases, signaling the breakdown of mean-field constraint theory, but in harmony with recent numerical results on self-organized networks.
TL;DR: The physics of soft-matter systems controlled by external fields is reviewed and previewed in this paper, with particular emphasis on statistical properties of well-characterized colloidal dispersions in different confining situations, in laser-optical, magnetic and electric fields as well as under shear.
Abstract: The physics of soft-matter systems controlled by external fields is reviewed and previewed. Particular emphasis is placed on statistical properties of well-characterized colloidal dispersions in different confining situations, in laser-optical, magnetic and electric fields as well as under shear. These are very active research areas where different complementary methods such as experiments, computer simulations and theory have been applied in parallel. Recently discovered novel phase transitions, generated and triggered by an external field, are described and the perspectives in this field for the next decade are discussed.