Type Of Phase Transition Research Articles

Magnetic phase diagram and dielectric properties of Mn doped CoCr2O4 nanoparticles

Abstract Effects of Manganese (Mn) substitution on the magnetic and dielectric properties of spinel phase Co1−xMnxCr2O4 (0.0 ≤ x ≤ 1) nanoparticles (NPs) have been studied. X-ray diffraction and Fourier transform infrared spectroscopy analysis showed the normal spinel structure for all the samples. Average crystallite size showed increasing trend with Mn doping and lies in the range 32–47 nm. The undoped CoCr2O4 NPs displayed a typical phase transition from paramagnetic (PM) to ferrimagnetic (FiM) state at TC = 100 K along with conical spiral magnetic state at TS = 27 K and lock-in transition state at TL = 13 K. The TC, TS and TL values were shifted towards lower temperatures with increasing Mn content and finally an antiferromagnetism (AFM) is obtained for MnCr2O4 NPs at TN = 20 K. A magnetic phase diagram was developed which showed the presence of different phases in these nanoparticles and attributed it to change in magnetic interactions with increasing Mn content. Saturation magnetization (MS) showed an increasing trend with Mn content due to the large magnetic moment of Mn ions. Nanoparticles showed an overall increasing trend of the dielectric constant with Mn concentration which is due to possible hopping of Mn2+ to Mn3+ and as well as increasing average crystallite size with Mn doping. In summary, increase in Mn doping revealed reduction in TC, TS, and TL values, an increasing MS trend, an AFM phase introduction and improved dielectric properties for Co1−xMnxCr2O4 NPs.

The influence of defect structure changes at phase transition on electrical properties in the Bi0.75Pr0.25O1.5 oxide ion conductor

The structural properties of Bi0.75Pr0.25O1.5 have been investigated by powder X-ray and neutron diffraction as a function of temperature up to around 800 °C. A layered rhombohedral structure is confirmed throughout the temperature range studied, with an order-disorder type phase transition (β2 ↔ β1) at ca. 730 °C. This transition is accompanied by partial migration of the oxide ions from the fluorite-like blocks of the layered structure to interstitial sites in the van der Waals gap between blocks. A reversible step change in total conductivity, associated with the phase transition, is preceded by non-linear behaviour observed in the Arrhenius plot of total conductivity at lower temperatures. A theoretical model based on a modification of the “cube-root” model successfully describes the conductivity data through the phase transition, showing the transition to involve a jump in inter-planar conductivity correlated with the appearance of interstitial oxide ions in the van der Waals gap. While the “cube root” model has been successfully used to explain phase transitions in classic 3-dimensional ionic conductors, the present study represents the first example of application of this model to a lower dimensional system.

Explosive phase transition in susceptible-infected-susceptible epidemics with arbitrary small but nonzero self-infection rate.

The ɛ-susceptible-infected-susceptible (SIS) epidemic model on a graph adds an independent, Poisson self-infection process with rate ɛ to the "classical" Markovian SIS process. The steady state in the classical SIS process (with ɛ=0) on any finite graph is the absorbing or overall-healthy state, in which the virus is eradicated from the network. We report that there always exists a phase transition around τ_{c}^{ɛ}=O(ɛ^{-1/N-1}) in the ɛ-SIS process on the complete graph K_{N} with N nodes, above which the effective infection rate τ>τ_{c}^{ɛ} causes the average steady-state fraction of infected nodes to approach that of the mean-field approximation, no matter how small, but not zero, the self-infection rate ɛ is. For τ<τ_{c}^{ɛ} and small ɛ, the network is almost overall healthy. The observation was found by mathematical analysis on the complete graph K_{N}, but we claim that the phase transition of explosive type may also occur in any other finite graph. We thus conclude that the overall-healthy state of the classical Markovian SIS model is unstable in the ɛ-SIS process and, hence, unlikely to exist in reality, where "background" infection ɛ>0 is imminent.

Later Stage Melting of Isotactic Polypropylene

The melting of crystals is a typical first-order phase transition. Pioneering experiments revealed that the melting of polymer crystals could be governed by the laws that were established based on ...

Quantum phases of a one-dimensional Majorana-Bose-Hubbard model

Majorana zero modes (MZM-s) occurring at the edges of a 1D, p-wave, spinless superconductor, in absence of fluctuations of the phase of the superconducting order parameter, are quintessential examples of topologically-protected zero-energy modes occurring at the edges of 1D symmetry-protected topological phases. In this work, we numerically investigate the fate of the topological phase in the presence of phase-fluctuations using the density matrix renormalization group (DMRG) technique. To that end, we consider a one-dimensional array of MZM-s on mesoscopic superconducting islands at zero temperature. Cooper-pair and MZM-assisted single-electron tunneling, together with finite charging energy of the mesoscopic islands, give rise to a rich phase-diagram of this model. We show that the system can be in either a Mott-insulating phase, a Luttinger liquid (LL) phase of Cooper-pairs or a second gapless phase. In contrast to the LL of Cooper-pairs, this second phase is characterized by nonlocal string correlation functions which decay algebraically due to gapless charge-$e$ excitations. The three phases are separated from each other by phase-transitions of either Kosterlitz-Thouless or Ising type. Using a Jordan-Wigner transformation, we map the system to a generalized Bose-Hubbard model with two types of hopping and use DMRG to analyze the different phases and the phase-transitions.

Symmetry-Adapted Finite Strain Landau Theory Applied to KMnF3

In recent years, finite strain Landau theory has been gradually developed as both a conceptual as well as a quantitative framework to study high pressure phase transitions of the group-subgroup type. In the current paper, we introduce a new version of this approach which is based on symmetry-adapted finite strains. This results in a substantial simplification of the original formulation. Moreover, it allows for replacing the clumsy use of truncated Taylor expansions by a convenient functional parametrization. Both the weaknesses of the traditional Landau approach based on infinitesimal strains as well as the major improvements made possible by our new parametrization are illustrated in great detail in an application to the ambient temperature high pressure transition of the perovskite KMnF 3 .

Thermogeometric study of van der Waals like phase transition in black holes: An alternative approach

It is well-known that the non-extremal anti-de-Sitter (AdS) black holes show various van der Waals type criticalities, such as the P−V, T−S, Y−X, Q2−Ψetc. In these cases, the phase space diagram of the relevant quantities are similar in behaviour to the isotherms on P−V diagram for the usual van der Waals gas system. The existing thermogeometric descriptions of these criticalities for the black holes deal with the whole thermogeometric manifold and its curvature. However, while observing the criticality, one only notices the behaviour of the relevant phase space variables and keep all other thermodynamic quantities as fixed. Therefore it is quite natural to investigate the geometrical behaviour of the induced metric, defined by these constant macroscopic variables, corresponding to the whole manifold of the thermogeometry. Using geometrothermodynamics (GTD), we precisely address this issue. It is observed that the extrinsic curvature of this induced metric also diverges at the critical point. This provides an alternative but important aspect of the thermogeometric description of phase transition of black holes. The entire formalism in this paper is very general as it is valid for any arbitrary black hole which shows the van der Waals type phase transition.

Rational Design of Ceramic-Like Molecular Ferroelectric by Quasi-Spherical Theory

Molecular ferroelectrics are attracting tremendous interest because of their easy and environmentally friendly processing, light weight, low acoustical impedance, and mechanical flexibility, which are viable alternatives or supplements to conventional ceramic ferroelectrics. However, reports of ceramic-like molecular ferroelectrics that can be applied in the polycrystalline form have been scarce. Here, according to the "quasi-spherical theory", we successfully synthesized a ceramic-like molecular ferroelectric with an m3mFmm2 type phase transition at 357 K, 1,5-diazabicyclo[3.2.1]octonium tetrafluoroborate ([3.2.1-dabco]BF4), which can show excellent ferroelectric performance in the polycrystalline thin-film form at room temperature. On the basis of the reported molecular ferroelectric [2.2.2-dabco]BF4 (2.2.2-dabco = 1,4-diazabicyclo[2.2.2]octonium) with an Aizu notation of 4/mmmFmm2 and two polar axes, we changed the [2.2.2-dabco]+ cation to the [3.2.1-dabco]+ cation to reduce the molecular symmetry and keep the quasi-spherical shape simultaneously, making the number of polar axes up to six. Moreover, the spontaneous polarization Ps gets successfully increased from 4.9 μC cm-2 in [2.2.2-dabco]BF4 to 5.5 μC cm-2 in [3.2.1-dabco]BF4. This precise molecular design strategy offers an efficient pathway to design ceramic-like molecular ferroelectrics.

A novel approach to the structural distortions of U/Th snub-disphenoids and their control on zircon → reidite type phase transitions of U1−xThxSiO4

Coffinite (USiO4) and thorite (ThSiO4) are conspicuous radiogenic silicates in the geonomy. They form U1−xThxSiO4 (uranothorite) solid solutions in zircon-type phase. Investigating the phase-evolution of these minerals is of utmost significance in realizing their applicability in the front-as well as at the back-end of nuclear industries. We carried out a systematic study of zircon- to reidite-type (tetragonal I41/amd to I41/a) structural transitions of U1−xThxSiO4 solid solution, and investigated their mechanical behaviour. We found a unique behaviour of transition pressure with the change in U-Th concentration in the solid solution. The phase transition pressure (p t) is found to be minimum for x = 0.5. We develop the necessary formalism and present an efficient method to estimate the longitudinal and angular distortions of U/ThO8-triangular dodecahedra (snub-disphenoids). We have parameterized two new factors: δ (longitudinal distortions) and σ2 (angular distortions) to quantify the polyhedral distortions. A detailed analysis of U/ThO8 snub-disphenoidal distortions is presented to address such variation of p t with U and Th concentration. We argue that our approach is independent of polyhedral volume and can be used for any AB8 (A: cation, B: anion) type snub-disphenoidal system.

Synthesis and characterization of thermo-responsive ionic liquids (TRILs)

Normally, an ionic liquids (ILs) is classified as hydrophilic or hydrophobic depending on its composition, whether it is miscible or immiscible with water. Nevertheless, this classification is ambiguous, since the miscibility of some ILs with water is strongly depending on temperature change. There are two classifications of thermo-responsive ionic liquids (TRILs) which are lower critical solution temperature (LCST) and upper critical solution temperature (UCST) behavior types. The aim of this study is to synthesis and characterize tetrafloroborate-based (BF4 −) anion with different alkyl chain of imidazolium- based cations ([Emim], [Bmim], [Hmim], [Omim]) and trifloroacetate (CFOO−) anion with different cations (ammonium, anilinium, pyridinium and phosphonium). The prepared ILs were mixed with water (30:70 wt %) and the resulting solutions were stirred vigorously for certain period of time. These solutions were cooled to 00C and then gradually heated to 70 0C. When the solution was found to be phase-separated upon heating, this mixture undergoes the LCST- type phase transition but its contrary with UCST behavioral. The TRILs were characterized using Fourier Transform Infrared (FTIR) to identify the functional group and Nuclear Magnetic Resonance (NMR) in confirming the structure. Due to the special property of TRILs that became phase separation by changing the temperature, it can be recovered easily and reused for many recycles in wide range of application.

Effect of W doping on phase transition behavior and dielectric relaxation of CuMoO4 obtained by a modified sol-gel method

Tungsten (W)-doped copper molybdate (CuMo1−xWxO4, x = 0∼0.12) compounds were prepared by the sol-gel method. The effects of doping content on the phase transition behavior and dielectric properties of CuMo1−xWxO4 (x = 0∼0.12) were investigated. X-ray diffraction and UV–vis diffuse reflectance spectroscopy clarified that W doping facilitated the transition of green α-phase to brown γ-phase. The chemical composition and structure of the CuMo1−xWxO4 (x = 0∼0.12) were investigated by Fourier transform infrared (FT-IR) spectroscopy and Raman spectra. The dielectric spectra of CuMo1−xWxO4 at −130 °C∼150 °C and the color-change of CuMo0.94W0.06O4 at 20 °C∼50 °C illustrated that the phase-transition temperature moves toward high temperature with increasing W. The functional relationship between the electrical modulus M’ and the frequency (1 Hz∼10 MHz) indicated that there are two dielectric relaxation mechanisms for CuMo1−xWxO4, which correspond to the polarization relaxation caused by hopping motion of polaron at low-temperature region (R1) and the relaxation dominated by oxygen vacancies at high temperatures (R2). It has also been confirmed that the phase transition of relaxation type exists in CuMo1−xWxO4, and that R1 occurs in γ-phase and R2 occurs in α-phase. It is of great significance to establish the dielectric relationship between phase transition and relaxation. With the content of W, the intensity of relaxation peak and activation energy of R1 did not change too much, but the relaxation behavior of R2 was inhibited and the activation energy increased gradually. The above results show that dielectric spectra are an important discovery as a new method to study the phase transition of materials, and is conducive to exploring the motion state of micro-particles. The control of phase-transition temperature is of great significance for this thermochromic material as a temperature sensor.

Дифракция плоской электромагнитной волны на микрошаре из VO-=SUB=-2-=/SUB=- в области фазового перехода

The paper presents the results of diffraction studies and the distribution of the electromagnetic (EM) field in a spherical particle of vanadium dioxide (VO2) before and after the metal-semiconductor phase transition (MSPT). As a result of calculations, it was shown that after the phase transition point in VO2 (T &gt; Tc), the EM wave radiation practically does not pass into the microsphere, but is almost completely reflected from it and scatters, which is associated with a sharp increase in the imaginary part of the dielectric constant of the microsphere and the transition of VO2 into the metal state, and the commensurability of the EM wavelength with the radius of the ball. It was also revealed that the radiation intensity at a distance of 2R from the surface of the spherical particle decreases sharply, which is associated with the interference of waves behind the particle (shadow region). From the modeling of diffraction and distribution of the EM field in the microsphere, we can propose a new method for studying of phase transitions of the MSPT type.

Одноионный механизм слабого антиферромагнетизма и спин-флоп-переход в двухподрешеточном ферромагнетике

The ground state of a Heisenberg ferromagnet with noncollinear single-ion anisotropy axes of two sublattices is investigated in the external magnetic field applied in the anisotropy axes plane. The noncollinearity of local anisotropy axes leads to new effect - the first order spin reorientation phase transition of the spin-flop type. The transition field depends on the value of anisotropy and orientation of the sublattice axes. Stability analysis of magnetic states shown that the field induced transition is accompanied by the magnetization hysteresis. The dependencies of the spin-flop transition field, the magnetization jump value and the susceptibility on the anisotropy parameters are determined. The obtained results are used for explanation of the magnetization field dependence in the ferromagnetic crystal PbMnBO_4.

Statistical Mechanics of Price Stabilization and Destabilization in Financial Markets

We build theory of market equilibrium by minimizing market’s free energy as a function of imbalance. A dark-soliton type of solution is found that describes a gradual transition from positive to negative imbalance as price increases, thus allowing for price uncertainty. Matching the empirical results, sudden security repricing by multiples of bid-ask spread results in a price crash with second-order type phase transition, while small repricing just leads to random walk. Lastly, we show how to use the developed theory to estimate price impact of a submitted order.

Study of phase transition of single crystal and polycrystalline vanadium dioxide nanofilms by using continuous laser pump-terahertz probe technique

As a typical phase transition material, vanadium dioxide has attracted much attention in the study of metal-insulator transition behavior since its phase transition temperature is close to room temperature. The experimental results of various modulation provide important clues to studying the vanadium dioxide phase transition mechanism. These experiments not only deepen the understanding of the strong correlation between electrons with different spins in various transition metal oxides, but also make an opportunity for exploring their potential practical applications. Although the phase transition mechanism of vanadium dioxide is still controversial, one has already made tremendous efforts to understand the mechanism of metal-insulation phase transition in the past few decades, which is stimulated from various experiments on vanadium dioxide modulation. Here in this work, the single crystal and polycrystalline vanadium dioxide are investigated. Their modulation mechanisms are studied by using the continuous laser pumping-terahertz probe technique, and it is found that the absorption behaviors of terahertz pulses at the same pump fluence are obviously different. After systematically discussing the representative phase transition mechanism, it is found that the phase transition of single crystal vanadium dioxide is attributed to the Mott-type phase transition dominated by the electronic structure, and that the polycrystalline vanadium dioxide originates from the Peierls-type phase transition occurring during the lattice distortion. In the past, most of the optical modulation was implemented under the condition of femtosecond laser pumping. The new optical modulation method given in this work, is a supplement to previous all-optical modulation experiment and more likely to be conducive to a more in-depth understanding of the modulation mechanism of vanadium dioxides.

Charged black hole chemistry with massive gravitons

In the subject of black hole chemistry, a broad variety of critical phenomena for charged topological black holes (TBHs) with massive gravitons (within the framework of dRGT massive gravity) is discussed in detail. Since critical behavior and the nature of possible phase transition(s) crucially depend on the specific choice of ensemble, and, in order to gain more insight into criticality in the massive gravity framework, we perform our analysis in both canonical (fixed charge, Q) and grand canonical (fixed potential, ) ensembles. It is shown that, for charged TBHs in the grand canonical ensemble, the van der Waals (vdW) phase transition could take place in , the reentrant phase transition (RPT) in and the analogue of triple point in , which are different from the results of the canonical ensemble. In the canonical ensemble, the vdW phase transition is observed in , the vdW type phase transition in and the critical behavior associated with the triple point in . In this regard, the appearance of grand canonical criticality and the associated phase transition(s) in black holes with various topologies depend on the effective topological factor instead of k in Einstein’s gravity, where k is the normalized topological factor ( plays this role in the canonical ensemble of TBHs in massive gravity). Such evidence gives the (grand) canonical study of extended phase space thermodynamics with massive gravitons a special significance.

Emergent bosons in the fermionic two-leg flux ladder

We study the emergence of bosonic pairs in a system of two coupled one-dimensional fermionic chains subject to a gauge flux (two-leg flux ladder), with both attractive and repulsive interaction. In the presence of strong attractive nearest-neighbor interaction and repulsive next-to-nearest-neighbor interaction, the system crosses into a regime in which fermions form tightly bound pairs, which behave as bosonic entities. By means of numerical simulations based on the density-matrix-renormalization-group (DMRG) method, we show in particular that in the strongly paired regime, the gauge flux induces a quantum phase transition of the Ising type from vortex density wave (VDW) to a charge density wave (CDW), characteristic of bosonic systems.

Synthesis and Thermoresponsive Properties of Biocompatible and Biodegradable Triblock Copolymers Bearing Linear or Y‐Shaped OEG Pendants

AbstractBiocompatible and biodegradable thermoresponsive polymers are of great interest in “smart” biomedical applications. Herein, triblock copolymers (6a and 6b) comprised of hydrophobic poly(propylene glycol) (PPG) and OEGylated polypeptides bearing Y‐shaped or linear pendants are prepared by ring‐opening polymerization of reactive N‐carboxyanhydride monomers and subsequent side chain modification of polypeptides. OEGylated triblock copolymer bearing Y‐shaped (6a) or linear pendants (6b) with similar main chain length and the same amount of oligo(ethylene glycol) (OEG) units are successfully prepared as verified by 1H NMR, FTIR, and GPC. CD analysis reveals that 6a with Y‐shaped OEG pendants shows thermal‐ or salt‐induced destabilization of α‐helical conformation in water. Both 6a and 6b show reversible lower critical solution temperature (LCST)‐type phase transitions in DI H2O or PBS. Incorporation of a PPG segment leads to a significant decrease of the LCST‐type cloud point temperature (Tcp). Consequently, 6a and 6b show Tcp to human body temperature at low polymer concentrations (≤0.5 mg mL−1 in PBS). Moreover, 6a and 6b show low in vitro cytotoxicity and biodegradability in the presence of proteinase K. The results indicate that the thermoresponsive properties of LCST‐type polymers can be readily tuned by constructing Y‐shaped pendants as well as incorporation of hydrophobic polymer building blocks.

Non-invasive acoustic fabrication methods to enhance collagen hydrogel bioactivity

Much attention has focused recently on utilizing components of the extracellular matrix (ECM) as natural building blocks for a variety of tissue engineering applications and regenerative medicine therapies. Consequently, new fabrication methods are being sought to enable molecular control over the structural characteristics of ECM molecules in order to improve their biological function. Exposing soluble collagen to acoustic forces associated with ultrasound propagation produces localized variations in collagen microfiber organization that in turn, promote cell behaviors essential for tissue regeneration, including cell migration and matrix remodeling. In the present study, mechanisms by which ultrasound interacts with polymerizing collagen to produce functional changes in collagen microstructure were investigated. The rate of collagen polymerization was manipulated by adjusting the pH of collagen solutions and the temperature at which gels were polymerized. Results demonstrate that the phase transition of type I collagen from fluid to gel triggered a simultaneous increase in acoustic absorption. This phase transition of collagen involves the lateral growth of early-stage collagen microfibrils and importantly, corresponded to a defined period of time during which exposure to ultrasound introduced both structural and functional changes to the resultant collagen hydrogels. Together, these experiments isolated a critical window in the collagen fiber assembly process during which mechanical forces associated with ultrasound propagation are effective in producing structural changes that underlie the ability of acoustically-modified collagen hydrogels to stimulate cell migration. These results demonstrate that changes in material properties associated with collagen polymerization are a fundamental component of the mechanism by which acoustic forces modify collagen biomaterials to enhance biological function.

The effects of operational thermal cycling on mechanical and magnetic properties of structural steels

This article shows the experimental results of the operational thermal cycling modeling of structural carbon steels with temperature range from the point of phase transition of type II cementite to the beginning of phase transformations of steel. In this study the influence of temperature that the number of thermal cycles and the histogram of temperature loading on the magnetic and mechanical properties of the steels were investigated. The possibilities of controlling the residual life of the elements, which are subjected to thermal cycling on changing the magnetic properties of metal, were determined. The functional dependence of the coercive force and hardness on the number of thermal cycles at a given temperature is obtained.