Apparent Phase Transition Research Articles

Re-entrant phase transitions in Laponite/Gum Arabic nanocomposites

A re-entrant gel transition is observed in a discotic clay, Laponite (Lap) aqueous suspensions with the addition of a complex polysaccharide, Gum Arabic (GA). For fixed concentrations of Lap (1–3 % w/v) and at low GA concentrations (CGA < 10 % w/v), the composites exhibit gel behaviour, while the suspensions undergo liquid phase separation for intermediate GA concentrations (10 % w/v < CGA < 20 % w/v). Gel behaviour is again observed in the samples at even higher GA concentrations (CGA > 30 % w/v). Here, we identify a thermodynamic phase transition in Lap/GA mixtures that is caused by a variation in GA content. The viscoelastic characteristics, phase transitions, and gelation kinetics of the Lap/GA mixtures have been studied by employing rheology, small-angle X-ray scattering, and optical investigations. Reduction of the negative values of zeta-potential and growth of the composite system's hydrodynamic size indicated the presence of interactions in Lap/GA mixtures. The phase diagram enables the apparent interactions and phase transitions between the nanoplatelets and the complex polysaccharides. Thus, our study provides new perspectives on a nanocomposite's tuneable rheological and structural features.

Optimizing energy storage performance of lead zirconate-based antiferroelectric ceramics by a phase modulation strategy

Dielectric energy storage has gained considerable significance owing to the high energy requirements of human society. Lead zirconate-based (PZ) antiferroelectric materials have received much attention due to their fast discharge rate, high power density, and low cost. Nevertheless, their low energy storage density seriously limits their practical applications. To overcome this limitation, the phase modulation strategy via chemical modification was adopted to optimize the breakdown strength and phase switching field. Specifically, the antiferroelectric ceramics of (Pb0.97−xGd0.02Srx)(Zr0.87Sn0.12Ti0.01)O3 were prepared by the tape-casting method. An apparent multistage phase transition behavior revealed for x ≥ 0.05 is rarely discussed in reported Sr2+ modified PZ system. This is attributed to the coexistence of the main orthorhombic phase and the tetragonal phase. Although the transition near the lower field reduces the energy storage slightly, the disruption of the long-range order stabilizes the antiferroelectricity of the orthorhombic phase, hence elevating its transition field. In addition, the tetragonal phase with lower polarization suppresses the electrostrain thus improving the breakdown strength. Consequently, an ultrahigh recoverable energy storage density of 14.5 J/cm3 with a high energy efficiency of 81 % is achieved at a high electric field of 717 kV/cm for (Pb0.92Gd0.02Sr0.05)(Zr0.87Sn0.12Ti0.01)O3. Moreover, the fatigue resistance of this composition is excellent within 26,000 fatigue cycles. Besides, it exhibits a high discharge energy density of 9.4 J/cm3 and a great power density of 387 MW/cm3. These results confirm that the energy storage properties of PZ-based antiferroelectric materials can be effectively optimized via a phase modulation strategy.

Dimorphism of [Bi2O2(OH)](NO3) - the ordered Pna21 structure at 100 K.

The re-investigation of [Bi2O2(OH)](NO3), dioxidodibismuth(III) hydroxide nitrate, on the basis of single-crystal X-ray diffraction data revealed an apparent structural phase transition of a crystal structure determined previously (space group Cmc21 at 173 K) to a crystal structure with lower symmetry (space group Pna21 at 100 K). The Cmc21 → Pna21 group-subgroup relationship between the two crystal structures is klassengleiche with index 2. In contrast to the crystal structure in Cmc21 with orientational disorder of the nitrate anion, disorder does not occur in the Pna21 structure. Apart from the disorder of the nitrate anion, the general structural set-up in the two crystal structures is very similar: [Bi2O2]2+ layers extend parallel to (001) and alternate with layers of (OH)- anions above and (NO3)- anions below the cationic layer. Whereas the (OH)- anion shows strong bonds to the BiIII cations, the (NO3)- anion weakly binds to the BiIII cations of the cationic layer. A rather weak O-H⋯O hydrogen-bonding inter-action between the (OH)- anion and the (NO3)- anion links adjacent sheets along [001].

Controllable Synthesis and Charge Density Wave Phase Transitions of Two-Dimensional 1T-TaS2 Crystals.

1T-TaS2 has attracted much attention recently due to its abundant charge density wave phases. In this work, high-quality two-dimensional 1T-TaS2 crystals were successfully synthesized by a chemical vapor deposition method with controllable layer numbers, confirmed by the structural characterization. Based on the as-grown samples, their thickness-dependency nearly commensurate charge density wave/commensurate charge density wave phase transitions was revealed by the combination of the temperature-dependent resistance measurements and Raman spectra. The phase transition temperature increased with increasing thickness, but no apparent phase transition was found on the 2~3 nm thick crystals from temperature-dependent Raman spectra. The transition hysteresis loops due to temperature-dependent resistance changes of 1T-TaS2 can be used for memory devices and oscillators, making 1T-TaS2 a promising material for various electronic applications.

Modeling the Transition between Localized and Extended Deposition in Flow Networks through Packings of Glass Beads

We use a theoretical model to explore how fluid dynamics, in particular, the pressure gradient and wall shear stress in a channel, affect the deposition of particles flowing in a microfluidic network. Experiments on transport of colloidal particles in pressure-driven systems of packed beads have shown that at lower pressure drop, particles deposit locally at the inlet, while at higher pressure drop, they deposit uniformly along the direction of flow. We develop a mathematical model and use agent-based simulations to capture these essential qualitative features observed in experiments. We explore the deposition profile over a two-dimensional phase diagram defined in terms of the pressure and shear stress threshold, and show that two distinct phases exist. We explain this apparent phase transition by drawing an analogy to simple one-dimensional mass-aggregation models in which the phase transition is calculated analytically.

Effect of speed fluctuations on the collective dynamics of active disks.

Numerical simulations are performed on the collective dynamics of active disks, whose self-propulsion speed (U) varies in time, and whose orientation evolves according to rotational Brownian motion. Two protocols for the evolution of speed are considered: (i) a deterministic one involving a periodic change in U at a frequency ω; and (ii) a stochastic one in which the speeds are drawn from a power-law distribution at time-intervals governed by a Poissonian process of rate β. In the first case, an increase in ω causes the disks to go from a clustered state to a homogeneous one through an apparent phase-transition, provided that the direction of self-propulsion is allowed to reverse. Similarly, in the second case, for a fixed value of β, the extent of cluster-breakup is larger when reversals in the self-propulsion direction are permitted. Motility-induced phase separation of the disks may therefore be avoided in active matter suspensions in which the constituents are allowed to reverse their self-propulsion direction, immaterial of the precise temporal nature of the reversal (deterministic or stochastic). Equally, our results demonstrate that phase separation could occur even in the absence of a time-averaged motility of an individual active agent, provided that the rate of direction reversals is smaller than the orientational diffusion rate.

Nonlinear Analysis of the Car-Following Model considering Delay under the V2X Environment

This paper proposes a model that analyzes the delay effect in V2X communication. V2X technology in the intelligent transportation system can realize the exchange of information between vehicles, people, and the environment. Still, more V2X links occupy many channel resources, and the occupation of channel resources leads to longer communication delays. Therefore, based on the optimal velocity of the car-following model, we model the channel delay in the V2X environment. The stability analysis results show that delay increases lead to system instability and traffic congestion. However, if more links are established, that is, the number of vehicles in the vehicle group ahead increases, traffic jams are less likely to occur. The numerical simulation results show that the longer the delay, the more serious the traffic congestion. In addition, we find an apparent phase transition region in the numerical simulation results, which is consistent with the theoretical analysis results. Therefore, in the intelligent transportation system, the delay caused by the complex electromagnetic environment is a factor that cannot be ignored, and thus the allocation of spectrum resources needs to be reasonably arranged. Otherwise, the V2X technology leads to traffic congestion.

Emergent strongly coupled ultraviolet fixed point in four dimensions with eight Kähler-Dirac fermions

The existence of a strongly coupled ultraviolet fixed point in four-dimensional lattice models as they cross into the conformal window has long been hypothesized. The SU(3) gauge system with eight fundamental fermions is a good candidate to study this phenomenon as it is expected to be very close to the opening of the conformal window. I study the system using staggered lattice fermions in the chiral limit. My numerical simulations employ improved lattice actions that include heavy Pauli-Villars (PV) type bosons. This modification does not affect the infrared dynamics but greatly reduces the ultraviolet fluctuations, thus allowing the study of stronger renormalized couplings than previously possible. I consider two different PV actions and find that both show an apparent continuous phase transition in the eight-flavor system. I investigate the critical behavior using finite size scaling of the renormalized gradient flow coupling. The finite size scaling curve-collapse analysis predicts a first-order phase transition consistent with discontinuity exponent $\ensuremath{\nu}=1/4$ in the system without PV bosons. The scaling analysis with the PV boson actions is not consistent with a first-order phase transition. The numerical data are well described by ``walking scaling'' corresponding to a renormalization group $\ensuremath{\beta}$ function that just touches zero, $\ensuremath{\beta}({g}^{2})\ensuremath{\sim}({g}^{2}\ensuremath{-}{g}_{\ensuremath{\star}}^{2}{)}^{2}$, though second-order scaling cannot be excluded. Walking scaling could imply that the eight-flavor system is the opening of the conformal window, an exciting possibility that could be related to 't Hooft anomaly cancellation of the system.

Ni Nanoparticles on Reducible Metal Oxides (Sm2O3, CeO2, ZnO) as Catalysts for CO2 Methanation

The activity of reducible metal oxide Sm2O3, CeO2, and ZnO as Ni nanoparticles support was investigated for CO2 methanation reaction. CO2 methanation was carried out between 200 °C to 450 °C with the optimum catalytic activity was observed at 450 °C. The reducibility of the catalysts has been comparatively studied using H2-Temperature Reduction Temperature (TPR) method. The H2-TPR analysis also elucidated the formation of surface oxygen vacancies at temperature above 600 °C for 5Ni/Sm2O3 and 5Ni/CeO2. The Sm2O3 showed superior activity than CeO2 presumably due to the transition of the crystalline phases under reducing environment. However, the formation of NiZn alloy in 5Ni/ZnO reduced the ability of Ni to catalyze methanation reaction. A highly dispersed Ni on Sm2O3 created a large metal/support interfacial interaction to give 69% of CO2 conversion with 100% selectivity at 450 °C. The 5Ni/Sm2O3 exhibited superior catalytic performances with an apparent phase transition from cubic to a mixture of cubic and monoclinic phases over a long reaction, presumably responsible for the enhanced conversion after 10 h of reaction. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Statistical mechanics of kinks on a gliding screw dislocation

The ability of a body-centered cubic metal to deform plastically is limited by the thermally activated glide motion of screw dislocations, which are line defects with a mobility exhibiting complex dependence on temperature, stress, and dislocation segment length. We derive an analytical expression for the velocity of dislocation glide, based on a statistical mechanics argument, and identify an apparent phase transition marked by a critical temperature above which the activation energy for glide effectively halves, changing from the formation energy of a double kink to that of a single kink. The analysis is in quantitative agreement with direct kinetic Monte Carlo simulations.

First-order transition in trigonal structure CaMn2P2

We report structural and physical properties of the single crystalline . The X-ray diffraction (XRD) results show that adopts the trigonal -type structure. Temperature-dependent electrical resistivity measurements indicate an insulating ground state for with activation energies of 40 meV and 0.64 meV for two distinct regions, respectively. Magnetization measurements show no apparent magnetic phase transition under 400 K. Different from other , Sr, and Ba, and , As, and Sb) compounds with the same structure, heat capacity and reveal that has a first-order transition at and the transition temperature shifts to high temperature upon increasing pressure. The emergence of plenty of new Raman modes below the transition, clearly suggests a change in symmetry accompanying the transition. The combination of the structural, transport, thermal and magnetic measurements points to an unusual origin of the transition.

An intrinsically flexible phase change film for wearable thermal managements

Phase change materials (PCMs) involving significant amounts of latent heat absorbing and releasing at a constant transition temperature have been extensively utilized for thermal management of electronic devices. However, it is still a great challenge to apply thermal management for wearable devices using PCMs due to their solid rigidity and liquid leakage. Although considerable efforts have been dedicated to constructing flexible composite PCMs by physically blending bulk PCMs with different flexible polymers, design and fabrication of intrinsically flexible PCM films still remain unexplored. Herein, we report an intrinsically flexible PCM film with apparent solid-solid phase transition performance, outstanding self-support and shape-conformable property for wearable thermal management. Remarkably, the as-obtained PCM film behaves adjustable phase transition enthalpy and temperature in the region from about (5 to 60)°C, long-term cycling stability up to 1000 cycles, highly mechanical flexibility and remarkable shape tailorability and foldability. Notably, such flexible PCM films are easily integrated into wearable devices with a flexible graphene film as thermal source, revealing superior temperature control behaviors, together with unprecedented electro-thermal and photo-thermal energy conversion performance. The intrinsically flexible PCM film developed in this work is holding great potential for next-generation flexible thermal management electronics.

Effects of Nano-Sized In2O3 on Sintering Behavior and Electrical Properties of 0.28Pb(In1/2Nb1/2)O3-0.40Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 Ceramics

0.28Pb(In1/2Nb1/2)O3-0.40Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 ceramics were synthesized by conventional solid-phase method using nano-sized In2O3. All the sintered 0.28PIN-0.40PMN-0.32PT ceramics have pure perovskite structure with composition locating at rhombohedral side around the morphotropic phase boundary (MPB) region. The 0.28PIN-0.40PMN-0.32PT ceramics belong to displacive driving ferroelectrics with apparent diffused phase transition characteristic. Although the rhombohedral-tetragonal ferroelectric phase transition temperature (TR-T) increases only to ∼120 °C due to the solid solution of Pb(In1/2Nb1/2) (PIN), the 0.28PIN-0.40PMN-0.32PT ceramics present high piezoelectric thermal stability till around the Curie temperature (Tm), which extremely widens the working temperature range and makes the 0.28PIN-0.40PMN-0.32PT ceramics suitable for high-temperature piezoelectric applications.

Zero-mode contribution and quantized first-order apparent phase transition in a droplet quark matter

The finite size effect on hadron physics and quark matter has attracted much interest for more than three decades, normally both the periodic (with zero-momentum mode) and the anti-periodic (without zero-momentum mode) spatial boundary condition are applied for fermions. By comparing the thermodynamical potential, it is found that if there is no other physical constraint, the droplet quark matter is always more stable when the periodic spatial boundary condition is applied, and the catalysis of chiral symmetry breaking is observed with the decrease of the system size, while the pions excited from the droplet vacuum keep as pseudo Nambu-Goldstone bosons. Furthermore, it is found that the zero-momentum mode contribution brings significant change of the chiral apparent phase transition in a droplet of cold dense quark matter: the 1st-order chiral apparent phase transition becomes quantized, i.e., the 1st-order apparent phase transition is completed in two steps, which is a brand-new quantum phenomena. It is expected that the catalysis of chiral symmetry breaking and the quantized 1st-order apparent phase transition are common features for fermionic systems with quantized momentum spectrum with zero-mode contribution, which also show up in quark matter under magnetic field.

Anharmonic Lattice Vibrations in Small-Molecule Organic Semiconductors.

The intermolecular lattice vibrations in small-molecule organic semiconductors have a strong impact on their functional properties. Existing models treat the lattice vibrations within the harmonic approximation. In this work, polarization-orientation (PO) Raman measurements are used to monitor the temperature-evolution of the symmetry of lattice vibrations in anthracene and pentacene single crystals. Combined with first-principles calculations, it is shown that at 10 K, the lattice dynamics of the crystals are indeed harmonic. However, as the temperature is increased, specific lattice modes gradually lose their PO dependence and become more liquid-like. This finding is indicative of a dynamic symmetry breaking of the crystal structure and shows clear evidence of the strongly anharmonic nature of these vibrations. Pentacene also shows an apparent phase transition between 80 and 150 K, indicated by a change in the vibrational symmetry of one of the lattice modes. These findings lay the groundwork for accurate predictions of the electronic properties of high-mobility organic semiconductors at room temperature.

Surface morphology and straight crack generation of ultrafast laser irradiated β-Ga2O3

Single crystal (010) β-Ga2O3 was irradiated by a Ti:sapphire ultrafast laser (150 fs pulse width) with varying fluences and a number of pulses in air ambient. Femtosecond laser-induced damage threshold of β-Ga2O3 is reported. Single pulse exposure results in surface morphological changes above a threshold laser fluence of 1.11 J/cm2. Laser-induced straight cracks aligned to the [001] crystallographic direction are observed in the laser irradiated regions, which are believed to be caused by laser-induced thermal stress, due to the unique low thermal conductivity and anisotropy associated with β-Ga2O3. Multiple pulse irradiation below the single pulse damage threshold fluence exhibited the formation of high spatial frequency laser-induced periodic surface structures. Electron backscattering diffraction and Raman spectroscopy suggested that there was no apparent phase transition of the irradiated β-Ga2O3 material for either single pulse or multiple pulse irradiation. This work serves as a starting point to further understanding the material properties of β-Ga2O3 and to unlock the potential for ultrafast laser material processing of β-Ga2O3.

High-Quality Magnetotransport in Graphene Using the Edge-Free Corbino Geometry.

We report fabrication of graphene devices in a Corbino geometry consisting of concentric circular electrodes with no physical edge connecting the inner and outer electrodes. High device mobility is realized using boron nitride encapsulation together with a dual-graphite gate structure. Bulk conductance measurement in the quantum Hall effect (QHE) regime outperforms previously reported Hall bar measurements, with improved resolution observed for both the integer and fractional QHE states. We identify apparent phase transitions in the fractional sequence in both the lowest and first excited Landau levels (LLs) and observe features consistent with electron solid phases in higher LLs.

Jamming analysis on the behaviours of liquefied sand and virgin sand subject to monotonic undrained shearing

It is well documented in the experimental literature that liquefied sands behave differently from virgin sands without a shearing history. In this study, undrained DEM simulations were performed on both a virgin sample and samples liquefied by cyclic loading. An identical critical state was reached regardless of liquefaction history. The fundamental mechanisms underlying the difference in the stress–strain responses between the liquefied sands and virgin sand were interpreted within the framework of jamming transition. The virgin sample was jammed throughout the simulation, characterised by a fully-percolated force transmission network of increasing resilience and mechanical stability. In contrast, the initially liquefied samples experienced an apparent phase transition from unjammed to jammed states. A fully-percolated force transmission network did not exist, and thus the unjammed samples flowed during the initial stage of loading. As loading proceeded, the force transmission network became fully percolated, and its resilience and mechanical stability developed. All of the micro-scale parameters reflecting the resilience and mechanical stability of the force transmission network reached identical values at the critical state independent of liquefaction history. Finally, a micro-scale approach based on the degree of indeterminacy was proposed to identify the four-stage post-liquefaction behaviour.

Synthesis of interpenetrating polymer networks using silicone polymer with silanol residue

Silicone polymers containing the silanol residue were prepared from a silica gel and were successively used for the synthesis of interpenetrating polymer networks (IPNs) with acrylamides, such as N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide. During gelation, the condensation of silanols to form a siloxane linkage and the radical polymerization of acrylamides with a cross-linker simultaneously proceeded to afford IPNs composed of both the silicone polymer and polyacrylamide gels. The swelling properties of the obtained IPNs were then investigated. For example, the IPNs synthesized with NIPAM showed a much lower percentage of equilibrium mass swelling (PES) values at 3 °C in water, 378–545%, than the NIPAM polymer gel (>1500%), and in addition, these IPNs barely showed an apparent volume phase transition temperature (VPTT) in contrast to the NIPAM polymer gel.

Influence of structure on the hardness and the toughening mechanism of the sintered 8YSZ/MWCNTs composites

Composites consisting of 8 mol.% yttria-stabilized zirconia (8YSZ) and 1 wt%, 5 wt% and 10 wt% multiwall carbon nanotubes (MWCNTs) have been prepared by attrition milling and spark plasma sintering (SPS). The effect of sintering temperature and MWCNT content on the microstructural features including apparent density, phase transition, crystal size and mechanical properties were investigated. The phase transformation during the sintering process was observed with X-ray diffraction. The MWCNT stability was investigated by Raman spectroscopy. Vickers hardness and indentation fracture toughness of 8YSZ/MWCNTs composites were evaluated and compared with reference 8YSZ composite. The crack propagation mechanisms of composites were determined. MWCNT pull-out, crack bridging and crack deflections were found and constituted a key factor of fracture toughness enhancement in the composites with MWCNT addition.