Type Of Phase Transition Research Articles

Structural characterisation, Hirshfeld surfaces, DSC, periodic DFT modeling, vibrational and optical study of heptylenediammonium pentachlorobismuthate H3N(CH2)7NH3BiCl5

A perspective hybrid material, NH3(CH2)7NH3BiCl5, was extensively characterized by structural, DSC, spectroscopic (FT-IR, FT-Raman, and UV-fluorescence) and theoretical (periodic DFT/GGA/PBE) methods. The structural features, noncovalent interactions between molecules in the crystal and electronic structure were examined and discussed in relation to the phase transitions, vibrational characteristics and optical properties. The compound crystallizes at 296 ​K in orthorhombic system (Pbcn space group, Z ​= ​8). The Cl⋯H/H⋯Cl intermolecular contacts act as the major contributor (77.2%) in the crystal. The compound was stable from the ambient temperature to 503 ​K, and it underwent one-reversible phase transition of second order type near 498 ​K, at heating. Characteristic bands in FT-IR (400-4000 ​cm-1) and FT-Raman (50-3500 ​cm-1) spectra were interpreted based on factor group analysis and calculated vibrational spectrum. The UV-fluorescence excitation at 396 ​nm and the visible region emission at 483 ​nm, which are of Cl(3p) ↔ Bi(6p) electron transition character, suggest potential applications as UV-filters and blue photoluminescent emmiters.

Temperature-Sensitive Localized Surface Plasmon Resonance of α-NiS Nanoparticles.

The presented work shows a synthesis route to obtain nanoparticles of the hexagonal α-NiS phase and core–shell particles where the same material is grown onto previously prepared Au seeds. In the bulk, this nickel sulfide phase is known to exhibit a metal–insulator type phase transition (MIT) at 265 K which drastically alters its electrical conductivity. Since the produced nanoparticles show a localized surface plasmon resonance (LSPR) in the visible range of the electromagnetic spectrum, the development of their optical properties depending on the temperature is investigated. This is the first time an LSPR of colloidal nanoparticles is monitored regarding such a transition. The results of UV–vis absorbance measurements show that the LSPR of the particles can be strongly and reversibly tuned by varying the temperature. It can be switched off by cooling the nanoparticles and switched on again by reheating them above the transition temperature. Additional to the phase transition, the temperature-dependent magnetic susceptibility of α-NiS and Au-NiS nanoparticles suggests the presence of different amounts of uncompensated magnetic moments in these compounds that possibly affect the optical properties and may cause the observed quantitative differences in the LSPR response of these materials.

High-pressure phase behavior of the quaternary system (carbon dioxide + dichloromethane + ε‒caprolactone + poly(ε‒caprolactone): Experimental data and PC-SAFT modeling

The phase behavior of the system containing carbon dioxide + dichloromethane + ε- caprolactone + poly(ε-caprolactone) was studied in order to get important information to understand the polymerization reaction in a high-pressure system. The experiments were performed using a variable-volume view cell over the temperature range from 323.15 to 353.15 K. The mass ratio between dichloromethane: (ε- caprolactone + poly(ε-caprolactone)) mixture was kept fixed at 1:1 with different poly(ε-caprolactone) mass fractions (reaction conversion) from 0.0 up 15.0 wt%. The mass composition of supercritical carbon dioxide varied in relation to the dichloromethane + ε- caprolactone + poly(ε-caprolactone) mixture from 60.0 to 77.5 wt% on dichloromethane free basis. Phase transitions of vapor-liquid bubble point type (VLE-BP) and liquid-liquid (LLE) were verified and lower critical solution temperature (LCST) behavior in P-W and P-T diagrams was observed. The experimental results were modeled using the PC-SAFT EoS, providing a positive representation of the experimental phase equilibrium data.

Multifunctional Flexible Vanadium Dioxide Films

ConspectusAs a typical phase transition material, vanadium dioxide (VO2) has attracted much attention due to its amazing metal–insulator transition (MIT) at the critical temperature of 68 °C, which could be driven by multiple stimuli, including electricity, thermal irradiation, THz waves, strain, etc. In the MIT process, VO2 exhibits significant changes in its structure from monoclinic structure at low temperature to rutile structure at high temperature, accompanied by significant modulation of physical properties, such as the infrared transmittance from high to low and a resistivity drop over 5 magnitudes. Based on these features, VO2 has functioned as thermochromic coatings, sensors, switches, electronic devices, actuators, etc. However, the vanadium element possesses multiple valent states and can produce complicated thermodynamics of vanadium oxides. The fabrication of tetravalence VO2 with desirable phase-transition features usually requires rigorous fabrication conditions with a precisely controlled atmosphere for stoichiometric components and high temperatures for good crystallinity. Under these circumstances, it is difficult to directly fabricate crystalline VO2 films on flexible polymer substrates because most of them could not stand such high temperatures (usually >400 °C), which will lead to the loss of the substrate functionality. However, the featured phase transition of VO2 makes it a promising candidate for future flexible devices, while VO2 owns great potential as flexible optical coatings, flexible sensors, flexible electronics, etc. Hence, research on flexible VO2 films is necessary and could largely pave the way to the application field of VO2 material. In this Account, we start with a brief introduction to phase transition properties of VO2 to reveal the intrinsic advantages as key materials in flexible devices. Next, multifunctional devices based on flexible VO2 films with different forms and characteristics are presented, including (1) flexible VO2-film-based thermochromic smart windows for energy-saving function depending on the change of environmental temperatures, (2) flexible VO2 films optical devices based on the changing emissivity of VO2, (3) flexible VO2 films with compatibility as multifunctional sensors, (4) next-generation flexible electronics based on VO2 films, and (5) flexible VO2 actuators with significant mechanical motions under external stimuli. Meanwhile, various fabrication technologies of flexible VO2 films have been introduced and discussed. Finally, we end the Account with an overview of the remaining challenges and new opportunities that have been opened up for vanadium dioxide in new forms of flexible optical and electronic devices. We hope this Account will inspire new innovative designs, fabrication approaches, and more possible functions of flexible VO2 films in future work.

Nonlinearly charged black hole chemistry with massive gravitons in the grand canonical ensemble

In the context of Black Hole Chemistry (BHC), holographic phase transitions of asymptotically anti-de Sitter (AdS) charged topological black holes (TBHs) in massive gravity coupled to Power Maxwell Invariant (PMI) electrodynamics are discussed in the grand canonical (fixed $U(1)$ potential, $\Phi$) ensemble. Considering all higher-order graviton's self-interactions of (dRGT) massive gravitational field theory in arbitrary dimensions, exact TBH solutions are derived, the explicit form of the on-shell action is computed, and the associated thermodynamic quantities in the Grand Canonical Ensemble (GCE) are calculated. In addition, the validity of the first law of thermodynamics and Smarr relation are examined in the extended phase space. Regarding this model, it is shown that a van der Waals (vdW) behavior takes place in $d \ge 4$ dimensions, a typical reentrant phase transition is observed in $d \ge 5$, and both anomalous vdW and triple point phenomena are recognized in $d \ge 6$. So, the results are quite different from their counterparts in the GCE of Maxwell-massive gravity. Besides, we briefly study the critical behaviors of higher-dimensional TBHs with a conformally invariant Maxwell source as a special subgroup of our solutions for both Einstein and massive gravity theories in various ensembles.

Phase Transformation Law of Nb Microalloyed Steel at Different Cooling Rates

Through the Gleeble3500 thermal simulation test machine, the phase transformation law of Nb microalloyed steel was studied and tested. After the compression deformation, it was cooled to room temperature at different speeds. Obtain the dynamic continuous cooling transformation diagram and the scanning structure diagram of the test steel, and then analyze the phase composition under different cooling speeds through JMatPro material performance simulation. The results show that: at a lower cooling speed (0.1°C/s), austenite decomposition is a diffusion-type phase change that takes place in a high-temperature region, and carbon atoms can diffuse sufficiently. At a moderate cooling rate (1°C/s), the bainite phase transition is a semi-diffusion phase transition in which carbon atoms are displaced in a non-cooperative thermally activated transition mode. When the cooling rate is high (15°C/s), the martensitic transformation is a non-diffusion-type transformation carried out in the low temperature region, and the atoms are directly transferred from the austenite lattice to the martensite lattice. With the increase of the cooling rate and the decrease of the transition temperature, from low-speed cooling→medium-speed cooling→high-speed cooling, respectively, the diffusion type phase transition→semi-diffusion type phase transition→the non-diffusion type phase transition. At different cooling rates, the continuous cooling transition diagram simulated by JMatPro is basically the same as the phase transition in the dynamic continuous cooling transition diagram of the test steel, which proves that the simulation prediction of the dynamic continuous cooling transition of the test steel by the JMatPro software has high accuracy and applicability.

Coupling dynamical and statistical mechanisms for baryonic cluster production in nucleus collisions of intermediate and high energies

Central nucleus-nucleus collisions produce many new baryons and the nuclear clusters can be formed from these species. The phenomenological coalescence models were sufficiently good for description of light nuclei yields in a very broad range of collision energies. We demonstrate that in reality the coalescence process can be considered as 1) the formation of primary diluted excited baryon clusters and 2) their following statistical decay leading to the final cold fragment production. We argue that the formation of such excited systems from the interacting baryons is a natural consequence of the nuclear interaction at subnuclear densities resulting in the nuclear liquid-gas type phase transition in finite systems. In this way one can provide a consistent interpretation of the experimental fragment yields (FOPI data) including the important collision energy dependence in relativistic ion reactions. We investigate the regularities of this new kind of fragment production, for example, their yield, isospin, and kinetic energy characteristics. A generalization of such a clusterization mechanism for hypernuclear matter is suggested. The isotope yields and particle correlations should be adequate for studying these phenomena.

On energy ground states among crystal lattice structures with prescribed bonds

We consider pairwise interaction energies and we investigate their minimizers among lattices with prescribed minimal vectors (length and coordination number), i.e. the one corresponding to the crystal’s bonds. In particular, we show the universal minimality—i.e. the optimality for all completely monotone interaction potentials—of strongly eutactic lattices among these structures. This gives new optimality results for the square, triangular, simple cubic (sc), face-centred-cubic (fcc) and body-centred-cubic (bcc) lattices in dimensions 2 and 3 when points are interacting through completely monotone potentials. We also show the universal maximality of the triangular and fcc lattices among all lattices with prescribed bonds. Furthermore, we apply our results to Lennard-Jones type potentials, showing the minimality of any universal minimizer (resp. maximizer) for small (resp. large) bond lengths, where the ranges of optimality are easily computable. Finally, a numerical investigation is presented where a phase transition of type ‘square–rhombic–triangular’ (resp. ‘sc-rhombic-bcc-rhombic-fcc’) in dimension d = 2 (resp. d = 3) among lattices with more than 4 (resp. 6) bonds is observed.

Chemical-Physical Behaviour of Microgels Made of Interpenetrating Polymer Networks of PNIPAM and Poly(acrylic Acid).

Microgels composed of stimuli responsive polymers have attracted worthwhile interest as model colloids for theorethical and experimental studies and for nanotechnological applications. A deep knowledge of their behaviour is fundamental for the design of new materials. Here we report the current understanding of a dual responsive microgel composed of poly(N-isopropylacrylamide) (PNIPAM), a temperature sensitive polymer, and poly(acrylic acid) (PAAc), a pH sensitive polymer, at different temperatures, PAAc contents, concentrations, solvents and pH. The combination of multiple techniques as Dynamic Light Scattering (DLS), Raman spectroscopy, Small Angle Neutron Scattering (SANS), rheology and electrophoretic measurements allow to investigate the hydrodynamic radius behaviour across the typical Volume Phase Transition (VPT), the involved molecular mechanism and the internal particle structure together with the viscoelastic properties and the role of ionic charge in the aggregation phenomena.

Studies of structural and electrical characteristics of multi-substituted Bi0.5Na0.5TiO3 ferroelectric ceramics

In this communication, preliminary structural and detailed electrical characteristics of the CaSnO3/CaSeO3-modified Bi0.5Na0.5TiO3 ceramics of a general chemical composition (1–2x) [Bi0.5Na0.5TiO3] + x (CaSnO3) + x (CaSeO3) with x = 0, 0.05, 0.10, 0.15, has been prepared by high-temperature solid-state reaction method with calcination and sintering temperature 925 °C and 950 °C, respectively, for 5 h. Structural and electrical characteristics of the parent compound have significantly been tailored by the addition of the equal percentage of CaSnO3, CaSeO3 over a wide range of temperature (25–400 °C) as well as frequency (1 kHz–1 MHz). Room-temperature X-ray diffraction (XRD) analysis confirms the development of single-phase compound (with rhombohedral symmetry) with very small amount of impurity phase in higher concentrations (x). In the dielectric spectroscopy, two dielectric peaks are observed at around the temperatures 210 °C and 320 °C indicating multiple phase transitions of different types including the ferroelectric to paraelectric through anti-ferroelectric. Impedance analysis of data exhibits both negative/and positive temperature coefficient of resistance of the materials. The Nyquist plots determine the grain and grain boundary effect in capacitive and resistive properties of the materials, and also the non-Debye type of relaxation. The room-temperature hysteresis loop confirms the existence of ferroelectricity in the compounds where as the leakage current characteristics determine the Ohmic behavior of the materials.

Unusual reversible fast-response dielectric and nonlinear optical switches in homochiral compounds

Two new materials with a fast dielectric response and a quadratic nonlinear optical switching property, (R)- and (S)-3-hydroxypiperidinium perchlorate ((R)- and (S)-3-HP-ClO4), have been synthesized. The homochirality of the cation causes asymmetry breaking, making the compounds crystallize in a chiral space group with special optical properties. By using differential scanning calorimetry (DSC) measurements, (R)- and (S)-3-HP-ClO4 undergo a typical first-order phase transition at 360 and 352 K, respectively. Similarly, the dielectric constants of the two enantiomers exhibit remarkable step-like anomalies around the phase transition temperatures. Moreover, the two enantiomers both show distinct switchable nonlinear optical (NLO) behaviors, which are caused by order–disorder transitions of the (R)- and (S)-3-(hydroxypiperidinium) cations and perchlorate anions. These findings have great potential in next-generation sensors, switches and actuator devices.

Multiple structural components and their competition in the intermediate state of antiferroelectric Pb(Zr,Ti)O3

Antiferroelectric perovskites form an important family of functional electric materials, which have high potential in energy storage and conversion applications. However, a full understanding of their crystal structural formation is still lacking. ${\mathrm{PbZrO}}_{3}$-based materials can serve as a model system for investigation, not only because ${\mathrm{PbZrO}}_{3}$ was the first discovered antiferroelectric, but also because it undergoes a typical phase transition sequence from a high-temperature paraelectric to the low-temperature antiferroelectric phase, passing through a possible intermediate phase that is poorly understood. Here we employ a combination of optical and scattering experiments and theoretical calculations to reveal the nature of the intermediate state. Evidence is found that this peculiar state consists of multiple short-range and long-range structural components, and their competition is crucial in stabilizing the antiferroelectric phase. External stimuli such as temperature change or chemical substitution can easily alter each component's energy landscape and thereby change the materials' electrical properties. These findings provide insights into understanding antiferroelectric-ferroelectric competition and can be useful in designing alternative antiferroelectric materials.

Microscopic Model of Intermediate Phase in Flexible to Rigid Transition

We introduce a lattice gas model with a modified Hamiltonian considering different energy for cycles of connected atoms. The system can be interpreted as a chalcogenide glass with pollutants forming floppy and rigid structures. We consider an energetic penalization for redundant bonds in the network. This penalization allows us to incorporate the topology constraints of rigidity in the network to study the thermodynamics of the system. We observe, depending on the parameter used for the penalization, that the system exhibits a typical first-order phase transition, or a stepped transition between the low and high density while varying the chemical potential. We also observe a hysteresis loop in the density and energy of the system. We use the area of these loops to calculate the irreversible enthalpy. There are two regimes, one where the enthalpy decreases linearly and the other with almost constant enthalpy. As the enthalpy is almost constant and very low, we interpreted this as the intermediate phase of the chalcogenide glasses.

Martensitic Transformation in Fe–Ni Alloys with Addition of Chromium, Manganese, and Carbon in High Magnetic Fields

The way in which martensitic transformation in iron alloys in high pulsed magnetic field can proceed via two different routes is explained. The first route corresponds to the Clausius–Clapeyron equation and can be considered “typical structural phase transition”. The second route is governed by the redistribution of the exchange-interaction forces between electrons in the fcc-lattice phase under the action of external factors which increase the interatomic distance (magnetostriction of paraprocess). Such a transformation route can be regarded as “the first-order magnetic phase transition”. In magnetic field, in some alloys the “structural phase transition” changes to “the first-order magnetic phase transition”. The hypothesis that the martensitic transformation in some steels and iron alloys can be regarded as “the first-order magnetic phase transition” even in the absence of a magnetic field (expansion of the lattice by spontaneous magnetostriction, carbon doping, etc.) is expressed.

Improved ferroelectric properties in hybrid improper ferroelectric Sr3−xBaxZr2O7

In the present work, Sr3−xBaxZr2O7 (x = 0.1, 0.2, 0.3) ceramics with Ruddlesden-Popper structures were prepared by a standard solid-state reaction method. The refinement results showed that the present ceramics formed a single orthorhombic phase with A21am space groups. The lattice constant and tolerance factor increased while the Curie temperature decreased linearly with increasing the content of barium cations, and the typical first-order improper ferroelectric phase transitions were determined in all ceramics. Moreover, the declines of oxygen octahedral rotation angle and coercive field were observed, while the enhanced remanent polarizations were found, therefore the improved ferroelectric properties were achieved by introducing the barium cations. The sharper decline of Curie temperature was induced by the hetero-valent substitution in contrast to the universal relationship between Curie temperature and tolerance factor. From the present work, the tolerance factor could not determine ferroelectric properties, and the possible way to improve ferroelectric properties was explored for Sr3Zr2O7-based ceramics.

Thermoelastic properties across martensitic transformation of Ni[formula omitted]MnGa Heusler alloy from time-resolved photothermal mirror

We report on the thermoelastic properties of Ni2MnGa shape-memory alloys across the martensitic to austenitic phase transition using the time-resolved pump–probe photothermal mirror technique. Quantitative information on the thermo-mechanical characteristics of the sample are obtained and compared to specific heat measurements and differential scanning calorimetry (DSC) analysis. The thermal diffusivity varied remarkably within the martensitic–austenitic transition range. Both the amplitude signal and the thermal diffusivity present, in addition to the strong martensite to austenite phase transition, a clear evidence of a subtle second-order type phase transition close to 80 °C. This magnetic transition is also observed in the calorimetric analysis. The transformation temperatures suggest the non-stoichiometric composition of sample, which is also revealed by non-symmetrical shapes of DSC peaks. The possible variation of the local chemical composition could be a result of gallium loss during the sample preparation or local inhomogeneity in the martensitic transformation.

Кинетика структурных фазовых переходов в сплаве Fe-=SUB=-80.5-=/SUB=-Ga-=SUB=-19.5-=/SUB=-

This work is devoted to the Monte Carlo simulation of the kinetics of phase transitions of the order-disorder type in the Fe80.5Ga19.5 alloy using the Blume-Emery-Griffiths Hamiltonian. The study of phase transformations was carried out in two stages: (1) different cooling rates (different number of Monte Carlo steps at a constant value of the binding energy); (2) isothermal annealing (the binding energy depends on the number of Monte Carlo steps at a fixed temperature). In the first case, a high cooling rate leads to one phase transition A2-> D03 + A2 at 700oС, while slow cooling leads to a transition A2-> D03 + A2 at 700oС through a mixture of phases A2, D03, B2 and L12 in the temperature range from 850 to 700oС. In the second case, an increase in the volume fraction of the L12 phase is shown with an increase in the duration of annealing at 750oС. Based on the data obtained, a thermokinetic diagram of phase transformations was constructed.

Dynamical phase transition and selective energy exchange in dual-cavity optochanical systems

<sec> In recent years, the cavity quantum photomechanics has been developed rapidly, and played a very important role in quantum information processing, quantum basic principle verification, and high-precision measurement. The kinds of quantum mechanical behaviors have also been explored and discovered in the study of cavity mechanics. By placing the Kerr medium in the system, quantum nonlinearity is introduced into the optomechanical system. Quantum phase transition is a relatively important part in the research of condensed matter physics. Since Dicke quantum phase transition was successfully observed experimentally, the problem of quantum phase transition in the optical cavity has attracted more attention. The spin-coherent-state variation method and the Holstein-Primakoff transformation are used to theoretically calculate the ground state energy functional, and the rich structure of the macroscopic multi-particle quantum state is given by adjusting the parameters. The quantum phase transition evolution equation describes the relationship between each phase and the time of generating a new phase when reaching the critical phase transition point. At the same time, the mode squeezing of multi-mode hybrid optomechanical system has also became one of the basic problems of quantum mechanical behavior in cavity quantum dynamics.</sec><sec> In this article, we explore the quantum dynamics of optomechanical devices including single-cavity and dual-cavities. We find that the system will undergo a dynamic phase transition, which is similar to the Dicke-Hepp-Lieb superradiant type phase transition, and a new dynamic critical point appears in the coupling between the momentum quadratures of the two optical fields. By manipulating the coupling parameters, we can achieve selective energy exchange between any two modes and the critical coupling point corresponds to selective energy exchange. Mode squeezing, which is easy to measure by applying the quantum uncertainty relationship, is also revealed and consistent with selective energy exchange. The study of coordinate and momentum variances gives us the revelation that the compressed orthogonal variables are the most suitable for measurement because of the small quantum noise. In fact, phononic modes can store energy in a longer duration, while photonic modes can transfer energy in a long distance. This phenomenon makes the hybrid optomechanical cavities useful in the next-generation quantum communications and quantum information processing units.</sec>

Conductive and Tough Smart Poly(N‐isopropylacrylamide) Hydrogels Hybridized by Green Deep Eutectic Solvent

AbstractConductive smart hydrogels with several virtues such as similar characters to biological tissues, sensitive response to ambient variations, have shown their excellent talents in the field of flexible electrical sensors, biomedical devices and directional transportation. However, complex preparing approaches or the instable inner structures have not only been time‐consuming, but also broken up the performance and reliability of the smart hydrogel‐based devices. In this work, a facile one‐step method is put forward to synthesize a kind of conductive poly(N‐isopropylacrylamide) (PNIPAM) hydrogel doped by a new green solvent of deep eutectic solvent (DES) containing choline chloride (ChCl) and acrylic acid (AA). Through the copolymerization of AA and NIPAM, the mechanical strength of the DES‐doped PNIPAM hydrogels is drastically improved compared to the pure PNIPAM gels, and some doped hydrogels lost the typical phase transition temperature of PNIPAM. Moreover, due to the ionic property of DES, the hybrid hydrogels also present the thermal‐depending conductivity as well as sensitive deformation response, which can be used as a smart switch in a circuit or a sensing element with environmental response ability. The cost‐effective preparation and the attractive performance of the DES‐doped hydrogels offer a new avenue to construct multi‐functional materials.

Phase evolution and associated electrical properties of Al-doped KNN–Bi0.5Na0.5ZrO3 lead-free piezoelectric ceramics

Samples of Al-doped (1–x)K0.5Na0.5Nb0.965Sb0.035O3–x(Bi0.82Al0.18)0.5Na0.5ZrO3 [((1–x)KNNS–xBANZ)] (x = 0.02, 0.03, 0.04, and 0.05) have been prepared by a conventional solid-state method. The results of XRD analysis suggest that the ceramics underwent a typical phase transition from orthorhombic (O) to tetragonal (T) as x was increased. According to the Raman shifts of key vibrational modes, lattice deformation and associated phase transition have been qualitatively deduced. Moreover, the ceramic with x = 0.05 exhibits enhanced piezoelectric properties compared with K0.5Na0.5NbO3 due to an O-T phase boundary (d33 ≈ 258 pC/N and kp ≈ 0.40). More importantly, the mechanism through which small ions function in a KNN lattice, as well as the phase transition, is addressed herein.