Kind Of Phase Transition Research Articles

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Applying pressure to hydrogen bonds significantly alters the bonding nature and induces various kinds of phase transitions. They are order-disorder transition, displacive transition, and bond symmetrization, and have intensively been investigated for ice as a prototype of a hydrogen-bonded system. The phase diagram of dense ice recently established at pressures up to 100 GPa and temperatures down to 0 K have revealed new aspects of physics and chemistry relating to the quantum behavior of protons such as tunneling. The phase relations and their physical implications are reviewed in this article.

Relationship Between the Shape of Suspension Particle and Ground State Structure of Electrorheological Solid

The effect of the shape of suspension particle in electrorheological (ER) fluid on the ground state structure of ER solid is discussed. The results of computation show that the ground state structure will change with the shape of suspension particle. This phenomenon is a kind of phase transitions that takes the shape factors of suspension particle as tuning parameters. The variation-value of interaction energy of the lattice structure of ER solid with the shape factors of suspension particle is sometimes noticeable.

Exhibition of intrinsic properties of certain systems in response to external disturbances.

Two systems, which are models of biological processes, are considered. These systems are notable for responding to different external actions nearly alike. This is associated with the fact that an external action excites only their natural intrinsic motions. Two kinds of external actions, harmonic and random, are studied. It is shown that each of them induces a transition to a new state that can be treated as a peculiar kind of phase transitions. Characteristics of these phase transitions are found.

Quantum Phase Transitions in One-Dimensional Peierls-Hubbard Model with Next-Nearest-Neighbor Hopping Integrals

Two kinds of phase transitions observed in the half-filled Peierls-Hubbard chain with the next-nearest-neighbor hopping integral are investigated. In the uniform case, according to the conformal field theory prediction, we numerically determine a phase boundary between the spin-fluid and dimer states. Then, the criticality of the spin-Peierls transition (i.e., powerlaw dependences of the energy gain and spin gap on the lattice dimerization parameter) is argued on the phase boundary.

High temperature phase transitions of CaTiO 3 and (Ca 0.85Nd 0.15)TiO 3 by X-ray diffractometry and differential thermal analysis

The two phase transitions of CaTiO 3 and (Ca 0.85Nd 0.15)TiO 3 were studied by high temperature X-ray diffraction and differential thermal analysis in the temperature range 300–1723 K. The presence of the two kinds of phase transitions in CaTiO 3 and (Ca 0.85Nd 0.15)TiO 3 at about 1390 K and about 1530 K recently found by the heat capacity measurement in our laboratory was confirmed. From the X-ray diffraction patterns of CaTiO 3 and (Ca 0.85Nd 0.15)TiO 3, the first phase transition at lower temperature was due to the change from the orthorhombic Pbnm to the orthorhombic Cmcm structure, and the second one at higher temperature was due to change from Cmcm to the cubic Pm3m structure, originating from the sequential rotations of the TiO 6 octahedra about one of the axes. Since no clear peak was seen at the phase transition around 1390 K in the DTA curve in contrast with the presence of the endothermic peak at the transition around 1530 K, it is thermodynamically considered that the former and the latter transition were second- and first-order phase transition, respectively.

On the Bose - Einstein condensation and phase transition of an n-dimensional ideal Bose gas

The general expressions of energy, heat capacity and Bose - Einstein condensation (BEC) temperature are given for an n-dimensional ideal Bose gas with a dispersion relation of , with which the possibility of occurrence of BEC can be determined. The curve of against temperature of the gas with is continuous at , while that of the gas with has a finite jump . These are two different kinds of phase transitions.

Fragmentation phase transition in atomic clusters I

The volume W of the accessible N-body phase space and its dependence on the total energy is directly calculated. The famous Boltzmann relation S = k * ln(W) defines microcanonical thermodynamics (MT). We study how phase transitions appear in MT. Here we first develop the thermodynamics of microcanonical phase transitions of first and second order in systems which are thermodynamically stable in the sense of van Hove. We show how both kinds of phase transitions can unambiguously be identified in relatively small isolated systems of ∼ 100 atoms by the shape of the microcanonical caloric equation of state 〈 T(E/N) ⌨ and not so well by the coexistence of two spatially clearly separated phases. I.e. within microcanonical thermodynamics one does not need to go to the thermodynamic limit in order to identify phase transitions. In contrast to ordinary (canonical) thermodynamics of the bulk microcanonical thermodynamics (MT) gives an insight into the coexistence region. Here the form of the specific heat c(E/N) connects transitions of first and second order in a natural way. The essential three parameters which identify the transition to be of first order, the transition temperature T tr, the latent heat q lat, and the interphase surface entropy Δs ssurf can very well be determined in relatively small systems like clusters by MT. It turns out to be essential whether the cluster is studied canonically at constant temperature or microcanonically at constant energy. Especially the study of phase separations like solid and liquid or, as studied here, liquid and gas is very natural in the microcanonical ensemble, whereas phase separations become exponentially suppressed within the canonical description. The phase transition towards fragmentation is introduced. The general features of MT as applied to the fragmentation of atomic clusters are discussed. The similarities and differences to the boiling of macrosystems are pointed out.

Competition between crystalline electric field singlet and itinerant states of f electrons

A new kind of phase transition is proposed for lattice fermion systems with simplified f^2 configurations at each site. The free energy of the model is computed in the mean-field approximation for both the itinerant state with the Kondo screening, and a localized state with the crystalline electric field (CEF) singlet at each site. The presence of a first-order phase transition is demonstrated in which the itinerant state changes into the localized state toward lower temperatures. In the half-filled case, the insulating state at high temperatures changes into a metallic state, in marked contrast with the Mott transition in the Hubbard model. For comparison, corresponding states are discussed for the two-impurity Kondo system with f^1 configuration at each site.

The transformation of fullerenes into diamond under different processing conditions

Three processes were used to transform fullerenes into diamond. (a) Laser irradiation processing. Diamond particles dispersed in an Fe C alloy system were obtained by CO 2 continous laser-induced quenching of fullerene coatings on carbon steel (C content 0.45%). The so-made fullrite, which achieved an average hardness of HRC65, contained a great deal of polygonal crystallites on the order of 0.1 micron, most of these being well-faceted cubic diamond. (b) Phase transition under high pressure processing: Fullerene carbon can transform to diamond with a good crystal morphology at high temperature (1450°C) and high pressure (5–6GPa). Furthermore, this kind of phase transition is easier and faster than that of graphite to diamond, both in homogeneous nucleation and in diamond crystal growth. (c)HF—CVD processing: Coating a Si wafer with fullerenes, a high quality diamond film can be deposited easily and quickly through the processing of HF CVD (Hot filament chemical vapour deposition). Both buckyballs and buckytube used as a coating agent have a significant effect on the diamond nucleation rate on Si substrates, buckytube performing better than buckyballs.

Nonlinear superposition of receptive fields and phase transitions

We present a principle of nonlinear superposition of receptive fields. Changes of connection weight, applied field or the distances between the input centers can lead to a new phase with all neurons encoding certain shapes excited. This process is a kind of phase transition and can be used for information processing.

Self-organized phase transitions in neural networks as a neural mechanism of information processing.

Transitions between dynamically stable activity patterns imposed on an associative neural network are shown to be induced by self-organized infinitesimal changes in synaptic connection strength and to be a kind of phase transition. A key event for the neural process of information processing in a population coding scheme is transition between the activity patterns encoding usual entities. We propose that the infinitesimal and short-term synaptic changes based on the Hebbian learning rule are the driving force for the transition. The phase transition between the following two dynamical stable states is studied in detail, the state where the firing pattern is changed temporally so as to itinerate among several patterns and the state where the firing pattern is fixed to one of several patterns. The phase transition from the pattern itinerant state to a pattern fixed state may be induced by the Hebbian learning process under a weak input relevant to the fixed pattern. The reverse transition may be induced by the Hebbian unlearning process without input. The former transition is considered as recognition of the input stimulus, while the latter is considered as clearing of the used input data to get ready for new input. To ensure that information processing based on the phase transition can be made by the infinitesimal and short-term synaptic changes, it is absolutely necessary that the network always stays near the critical state corresponding to the phase transition point.

A phenomenological approach to salient maps and illusory contours

This paper presents a new general approach to salient maps and illusory contours. We first formulate an energy model for representing line contours with a set of line segments of different geometric redundancy. New items incorporated into the energy are marginal energy, point energy and exchange interaction. Marginal energy and exchange interaction induce several kinds of bound energy, which provides a general solution to the segmentation/grouping/binding problem. Salient maps and illusory contours emerge out of images at some critical points as a kind of phase transition and thus can be detected in parallel at the early vision stages. These phase transitions, with no obvious hysteresis, have interesting behaviour including crossovers. The energy model, providing some intuition to the strategies for visual representation by the brain, may be related to the retinotopic mapping and the functional columnar architecture of the brain cortex and casts some doubts on the present computational theory of vision.

Two kinds of phase transition in 1-D backward scattering

The one-dimensional Fermion system with backward scattering has been analyzed by use of the methods of bosonization and Gaussian wave functional. We find that there exist two kinds of phase transitions in the spin density degree according to the interaction parameters: one is a Kosterlitz-Thouless type transition and the other is a first order phase transition when backward scattering becomes sufficiently strong.

High-pressure studies of high-concentration phases of the Ti[sbnd]H system

In situ X-ray diffraction at high pressure (5 GPa) and high temperatures (less than or approximately 1100 °C) of the TiH system revealed that two different kinds of phase transition take place at high hydrogen concentrations. [H]/[Ti] ≳ 2, a reversible transition due to absorption-desorption of hydrogen and an irreversible transition due to the formation of metal-atom vacancies. The general implication of the formation of defect-hydride phases in the phase diagrams of MH systems is discussed.

Phase transitions in the uniformly frustrated XY model with frustration parameter f=1/3 studied with use of the microcanonical Monte Carlo technique.

We study the phase transition of the frustrated XY model in the square lattice with frustration f=1/3. The system has a discrete ${\mathit{Z}}_{3}$\ifmmode\times\else\texttimes\fi{}${\mathit{Z}}_{2}$ symmetry and a continuous U(1) symmetry. We study the system via the microcanonical Monte Carlo technique. We have found that the system has three kinds of phase transitions. At the temperature 0.208J/${\mathit{k}}_{\mathit{B}}$, the system has a Kosterlitz-Thouless transition with a larger-than-universal jump in the helicity modulus. At the temperature 0.215J/${\mathit{k}}_{\mathit{B}}$, the system has a vortex-lattice melting transition related to discrete ${\mathit{Z}}_{2}$ symmetry. At some higher temperature 0.219J/${\mathit{k}}_{\mathit{B}}$, the system has a second-order vortex-lattice melting transition related to ${\mathit{Z}}_{3}$ symmetry. It is also found that the second transition gives a weak anomaly of the specific heat while the third transition gives rise to the divergence in the specific heat.

Calorimetric and resistometric studies of La2CuO4+ δ single crystals: Displasive character of phase transitions in 190–310 K

Measurements of heat capacity, resistivity, and magnetic susceptibility for the La 2CuO 4+δ single crystals in the range 0.001≤ δ≤0.035 revealed that following four kinds of phase transitions appear between 10 and 320 K: superconducting transition around 33 K, a transition around 200 K with small heat anomaly, martensitic transition around at 250–270 K, and a second order transition at 295 K. These transition temperatures strongly depended on the amount of excess oxygen content. The heat capacity anomalies for the sample with δ=0.035 in the range of 190 to 310 K were interpreted as connected with cooperative displacements of ions involving no diffusion process of oxygen ion.

Observation of Phase Transition of Liquid Crystalline Polymers by Ultrasonic Method. (Hydroxypropyl)cellulose and (n-Hexanoyloxypropyl)cellulose

Using ultrasonic measurements, phase transition behavior was examined for (hydroxypropyl)cellulose (HPC) in solution and (n-hexanoyloxypropyl)cellulose (HPC-C6) in bulk. For various kinds of HPC solutions, we observed a phase transition of Landau–Khalatnikov type in the variation of ultrasonic variables with polymer concentration. It is the first observation for lyotropic liquid crystalline polymer systems, so far as we know. The critical concentration varied with species of solvent and it became higher in the order of acetic acid, ethyl alcohol, dioxane, and water. For HPC-C6 in bulk, we found at least two kinds of phase transitions in the variation of ultrasonic variables with temperature. One of them is ascribable to the phase transition between liquid crystalline and isotropic phases (i.e., the phase transition of the first kind). Another phase transition may be one of the second kind, in the case in which one could not detect by conventional methods. Thus, it was found that ultrasonic method is very useful to study the phase transition behavior.

Phase transition from periodic to quasiperiodic behaviour in 4D cellular automata

We have found a phase transition from periodic to quasiperiodic behaviour in four-dimensional cellular automata by mixing rules. As far as we know, this kind of phase transition has not been studied before, and may thus serve as a pilot case.

Magnetic resonance of fullerene solids and their compounds

Nuclear magnetic resonance (NMR) measurements on the novel materials C 60 and C 70, and their compounds with the alkali metals, are reported and reviewed. A sharp change in the NMR relaxation time t 1 at 263 K with a hysteresis of 1 K corresponding to an orientational phase transition was found in sublimed C 60 powder. A similar abrupt change in T 1 −1 at 280 K was also found in sublimed C 70 powder, which is ascribed to the same kind of phase transition as found in C 60, although here it is restricted to uniaxial rotation around the long ellipsoidal axis and unlike free rotation in the case of C 60. At temperatures above 340 K however, three-dimensional free rotation can take place. A curious behavior of the ESR intensity was observed for the pure C 60 powder. The ESR intensity strongly decreased upon exposure of air instead of the expected increase upon exposure to oxygen and light. 13C NMR T 1, measurements on the three superconducting compounds were analyzed in terms of a relation between Tinc and the density-of-states at the Fermi energy.

Electrical Properties and Phase Transitions in Superconducting Quasi-One-Dimensional Chalcogenides InxNb3X4 (X = S, Se, and Te)

Electrical properties and phase transitions were investigated in the quasi-one-dimensional ternary chalcogenides InxNb3X4 (X = S, Se, and Te; x = 0.5 for X = S, and 1.0 for X = Se and Te), with results indicating that the InrNb3Te4 system has two new kinds of phase transitions. Based on the values of the transition temperatures Tt, this system is classified into two groups, i.e., Group 1 samples with 0 ≤ x < 0.55 having T1 = ≈40 and ≈80 K, and Group 2 samples with 0.55 < x ≤ 1.0 having Tt = ≈50 and = 140 K. Electron diffraction measurements showed the 140-K transition to be associated with a charge-density-wave (CDW) formation accompanied by the appearance of a superstructure that can be explained by the commensurate wave vectors q = ±(13a* + 13b* + 19c*, which are slightly larger in the c* component as compared with those previously observed in Nb3Te4 of q = ±(13a* + 13b* + 37c* . The increase in the c * component was interpreted as being caused by the increase in Fermi energy due to In insertion. Thermopower measurements on InxNb3Te4 showed the dominant carriers to be holes. In addition, the InxNb3Se3.84 system (0.40 ≤ x ≤ 1.0) showed a new CDW-like transition at ≈30 K. The superconducting critical temperature Tc of InxNb3X4 was increased by several degrees when the in content x was increased above 0.5.