Mechanism Of Phase Transition Research Articles

Crystallographic types depended energy storage mechanism for zinc storage

As a new type cathode material for aqueous zinc-ion batteries (ZIBs), manganese-based sulfides have gradually received researchers’ concern in recent years due to their lower electronegativity, higher electronic conductivity and better electrochemical activity compared with the corresponding manganese-based oxides. However, the revelation of energy storage mechanism for manganese-based sulfides is full of great challenges, which largely restricts their application. Herein, inspired by density functional theory calculations, we design and synthesize the γ-MnS and α-MnS hollow microspheres with different crystallographic types for the first time, delivering significantly different energy storage mechanisms of the two MnS electrodes. Impressively, the γ-MnS electrode can stably exist and store energy during the whole charging/discharging processes, while the α-MnS electrode first undergoes irreversible in situ oxidation to generate ZnMnO3/MnOx during the initial charging process, and then the reversible H+/Zn2+ co-insertion/extraction energy storage behavior occurs during the subsequent discharging/charging processes. This unique phase transition mechanism caused by in situ electrochemical oxidation enables the α-MnS electrode to achieve enhanced ion diffusion kinetics, thereby improving the rate capability and cyclic stability. This work not only enriches the energy storage mechanism of manganese-based sulfide cathodes, but also offers research ideas for the design and development of advanced manganese-based cathodes.

Terahertz flexible multiplexing chip enabled by synthetic topological phase transitions.

Flexible multiplexing chips that permit reconfigurable multidimensional channel utilization are indispensable for revolutionary 6G terahertz communications, but the insufficient manipulation capability of terahertz waves prevents their practical implementation. Herein, we propose the first experimental demonstration of a flexible multiplexing chip for terahertz communication by revealing the unique mechanism of topological phase (TP) transition and perseveration in a heterogeneously coupled bilayer valley Hall topological photonic system. The synthetic and individual TPs operated in the coupled and decoupled states enable controllable on-chip modular TP transitions and subchannel switching. Two time-frequency interleaved subchannels support 10- and 12-Gbit/s QAM-16 high-speed data streams along corresponding paths over carriers of 120 and 130GHz with 2.5- and 3-GHz bandwidths, respectively. This work unlocks interlayer heterogeneous TPs for inspiring ingenious on-chip terahertz-wave regulation, allowing functionality-reconfigurable, compactly integrated and CMOS-compatible chips.

Phase transition mechanism of CsPbI2Br perovskite films induced by moisture

The humidity stability and phase transition mechanism of the all-inorganic perovskite CsPbI2Br based on an optimized dual-source co-evaporation preparation process are investigated at the film interface level. It is found that the CsPbI2Br films annealed at 300 °C for several minutes exhibit a best crystallinity and photoelectric properties. The as-grown CsPbI2Br film is confirmed to be a α phase with a dark brown cubic crystal structure and an average visible transparency of 35.9%. But it will be transformed into its δ phase with a transparent orthorhombic crystal structure and an average visible transparency of 80.3% after a certain amount of moisture exposure. Compared with the α phase film, the electronic structure of the δ phase has also changed significantly with a VBM shift of about 0.32 eV to high binding energy. The results of AR-XPS show that the water molecules in perovskite CsPbI2Br after a moisture exposure only adsorb on the surface rather than penetrate the interior of the lattice. When water molecules adsorb on the lattice surface, halide ions should migrate towards the lattice surface due to their high hydration enthalpy, resulting in halide vacancies within the lattice and causing the reduction of energy barrier for phase transition from α phase to δ phase. So the CsPbI2Br film will transform from its α phase to δ phase induced by water vapor, and this phase transition will be reversed to some extent after another annealing.

Three-dimensional ultrafast charge-density-wave dynamics in CuTe

Charge density waves (CDWs) involved with electronic and phononic subsystems simultaneously are a common quantum state in solid-state physics, especially in low-dimensional materials. However, CDW phase dynamics in various dimensions are yet to be studied, and their phase transition mechanism is currently moot. Here we show that using the distinct temperature evolution of orientation-dependent ultrafast electron and phonon dynamics, different dimensional CDW phases are verified in CuTe. When the temperature decreases, the shrinking of c-axis length accompanied with the appearance of interchain and interlayer interactions causes the quantum fluctuations (QF) of the CDW phase until 220 K. At T < 220 K, the CDWs on the different ab-planes are finally locked with each other in anti-phase to form a CDW phase along the c-axis. This study shows the dimension evolution of CDW phases in one CDW system and their stabilized mechanisms in different temperature regimes.

Indications for an alternative breaking of symmetry in fracture-induced electromagnetic emissions recorded prior to the 2023 Mw7.8 and Mw7.5 Turkey Earthquakes

Several evidence has been reported corroborating the view that the MHz band fracture-induced electromagnetic emissions (FEME), also known as fracture-induced electromagnetic radiation (FEMR), which are detected prior to shallow main earthquakes (EQs) of moment magnitude Mw>5.5 with epicenters on land or near coastline, can be studied in analogy to a Z(2) spin system undergoing a second-order phase transition. Specifically, by analyzing MHz FEME/FEMR time series recorded prior to several earthquakes in the past >20 years, information has been extracted about the organization to critical state, the critical state itself, as well as for the step-by-step development of the spontaneous symmetry breaking (SSB) phenomenon. Using the “method of critical fluctuations” (MCF) and a recently proposed method for the wavelet-based detection of scaling behavior in noisy experimental data, we identified for the first time a different way of breaking the symmetry embedded in the MHz FEME/FEMR time series recorded by the hELlenic Seismo-ElectroMagnetics Network (ELSEM-Net) prior to the devastating (Mw=7.8 and Mw=7.5) EQs that occurred in south-east Turkey on 06/02/2023. Particularly, after the achievement of the critical state, indications were found that, although the underlying system started to break the symmetry according to the second-order phase transition mechanism (through SSB), SSB was not completed. Instead, the system seems to have changed symmetry and presented indications that the break of symmetry was finally achieved according to the first-order phase transition mechanism. Specifically, after the incomplete SSB, it was found to present tricritical behavior, followed by indications of triple degeneration of the order parameter fixed-point. This change of behavior observed in the MHz FEME/FEMR is a puzzling phenomenon for several reasons, which are discussed in detail, whereas suggestions are expressed as a first attempt for the possible explanation of the new findings.

Phase transition mechanism and long‐term stability of LiF‐assisted sintered Li2MgxZrO3+x microwave dielectric ceramics

AbstractHerein, Li2MgxZrO3+x (x = 0–1) +2 wt.% LiF ceramics with a rock salt structure were prepared by the solid‐state reaction method. The phase transition mechanism was systematically investigated by X‐ray diffraction, and first‐principles calculations. With a gradual increase in MgO content, the samples underwent a monoclinic‐Li2ZrO3 to tetragonal‐Li2ZrO3 to tetragonal‐Li2MgZrO4 to cubic‐phase transition. The variations of the microwave dielectric properties due to the phase transition were systematically analyzed by the multi‐phase mixtures law. In addition, CO2 adsorption of the samples was quantitatively analyzed by X‐ray photoelectron spectroscopy, and the long‐term stability of the Q × f of the samples was investigated. The optimal microwave dielectric properties were obtained in Li2Mg0.2ZrO3.2 ceramic at 950°C: εr = 19.5, Q × f = 44 500 GHz, and τf = 2.6 ppm/°C. In addition, the ceramic samples were compatible with Ag, which indicates that Li2MgxZrO3+x (x = 0−1) +2 wt.% LiF is a promising material for low‐temperature co‐fired ceramics.

Experimental investigation and modeling on the dissociation kinetics of methane hydrate in clayey silt cores in depressurization

Natural gas hydrate (NGH) in clayey silts might be the majority of its global reserve. A thorough understanding on the dissociation kinetics of NGH in clayey silts is crucial for its safe and efficient exploitation. In this study, the dissociation characteristics of methane hydrate in quartz silts, montmorillonites and South China Sea (SCS) sediments made cores in multi-step depressurization was experimentally studied and modeled. In quartz silt core, methane hydrate thoroughly dissociated once the pressured is lowered to the equilibrium pressure in bulk. In montmorillonite and SCS sediment cores, methane hydrate dissociation initiated at higher pressure than quartz silt. Capillary and clay induced water activity depressions are suggested to be the major causes. Stepwise methane hydrate dissociation was discovered in the montmorillonite and SCS sediment cores in multi-stage depressurization. In one step depressurization, hydrate in the fine grain cores with larger surface area dissociated faster. In montmorillonite and SCS sediment cores, lower water content leads to faster dissociation at the same pressure, which may be attributed to the higher driven force for dissociation (fugacity difference fe-f). A kinetic model for NGH dissociation in clayey silts was established by introducing fitted equivalent diameter and surface area correction factor of hydrate particles to the Kim-Bishnoi model. In the model, the hydrate equilibrium conditions in clayey silts were predicted by the water activity measurement (WAM) technique. With a maximum deviation of 9.81% in gas production, the model prediction and experimental results are in good agreement. The experimental findings and model reported in this work may be helpful to understand the NGH phase transition mechanism in clayey silt sediments.

Investigation of the liquid water content in composite saline soil containing chloride and sulfate ions

Different salt types have different effects on the liquid water content of saline soil, resulting in differences in the physico-mechanical properties and water/salt migration process of saline soil. In order to investigate the phase transition process and the change of the liquid water content in composite saline soil, saline soils with the same total salt content and different ratios of sodium chloride and sodium sulfate were taken as the objects. The results indicated that two phase transitions occur in the saline soil with single salt type, while three phase transitions can be found in the composite saline soil with two salt types. Mirabilite crystallization contributes to the 1st phase transition, mirabilite and ice precipitate together in the 2nd phase transition process, and mirabilite, ice, and hydrohalite precipitate simultaneously in the 3rd phase transition process. The liquid water is reduced in the phase transition process during cooling, and the pore characteristic has been changed significantly. The change of the liquid water content reflects the processes of salt crystallization and ice formation in saline soil, then the amounts of ice and hydrated salt were calculated at different temperatures, and the mechanism of inhibiting the deformation of sulfate saline soil was examined by adding sodium chloride. The results have reference value for those seeking understanding of the deformation in natural composite saline soil, and these findings can provide theoretical basis for the phase transition mechanism of saline soil in cold regions.

Coexisting Magnetism, Ferroelectric, and Ferrovalley Multiferroic in Stacking-Dependent Two-Dimensional Materials.

Two-dimensional (2D) multiferroic materials have widespread application prospects in facilitating the integration and miniaturization of nanodevices. However, the magnetic, ferroelectric, and ferrovalley properties in one 2D material are rarely coupled. Here, we propose a mechanism for manipulating magnetism, ferroelectric, and valley polarization by interlayer sliding in a 2D bilayer material. Monolayer GdI2 is a ferromagnetic semiconductor with a valley polarization of up to 155.5 meV. More interestingly, the magnetism and valley polarization of bilayer GdI2 can be strongly coupled by sliding ferroelectricity, making these tunable and reversible. In addition, we uncover the microscopic mechanism of the magnetic phase transition by a spin Hamiltonian and electron hopping between layers. Our findings offer a new direction for investigating 2D multiferroic devices with implications for next-generation electronic, valleytronic, and spintronic devices.

The role of Ca/Zr ratio on the local structure and phase transitions in lead-free (Ba,Ca)(Zr,Ti)O3

In this study, the structural phase transitions are investigated as a function of composition and temperature for polycrystalline x(Ba0.7Ca0.3)TiO3-(1 − x)Ba(Zr0.2Ti0.8)O3 (x = 0.40, 0.45, 0.50, 0.55, and 0.60) through a combination of Raman spectroscopy, synchrotron X-ray diffraction, and dielectric spectroscopy. The aim is to gain insight into the complex phase boundary region responsible for the excellent electromechanical properties. The results demonstrate the correlation between local site substitutions based on the stoichiometric variations to the microstructure and dielectric properties. The dielectric response has been correlated with the BCT/BZT content displaying a maximum depending on the phase content. Additionally, in situ temperature-dependent Raman, permittivity, and pair distribution function (PDF) studies were performed from −60 °C to 130 °C to highlight the structure and phase evolution. In particular, the in situ temperature-dependent Raman measurements reveal sudden discontinuities in the vibrational modes that correspond to the structural changes in the perovskite structure. Therefore, the results of the permittivity response, based on the average of a large volume, are consistent with the local structural changes obtained by other techniques. Indeed, correlations of Raman, X-ray diffraction, and PDFs obtained from synchrotron X-ray total scattering data, along with permittivity measurements allowed the identification of the discrete ferro- to paraelectric phase transitions and a more robust characterization. The rotation and distortion of the octahedral caused by oxygen displacement are driving forces behind symmetry changes and phase transitions, explaining the mechanism of polymorphic phase transition based on A- and B-site substitution. Therefore, this work provides a comprehensive understanding of temperature and composition-dependent phase transitions in BCZT.

Heterogeneous precipitate microstructure design in β-Ti alloys by regulating the cooling rate

Cooling after solutionizing or aging plays a crucial role in heat treatment and can greatly influence the final precipitate microstructure and mechanical properties of titanium (Ti) alloys. In this study, we employ phase field simulations to strategically engineer heterogeneous precipitate microstructures in near β-Ti alloys by manipulating the cooling rate, which leads to different phase transition mechanisms. By varying the cooling rate within the temperature range of 900 ∘C to 500∘C, we identify four distinct microstructures: uniformly distributed fine congruent αc plates and fine α precipitates, heterogeneous and hierarchical α precipitates, and uniformly distributed coarse α precipitates. Further analysis reveals that these diverse precipitate microstructures originate from three distinct phase transition mechanisms, i.e., congruent transition, pseudospinodal decomposition, and classical nucleation and growth, each activated at different temperatures during continuous cooling. Utilizing the insights from the simulations, we successfully produce microstructures in Ti-5Al-5Mo-5V-3Cr-1Zr (Ti55531) with heterogeneous α precipitates by applying intermediate cooling rates (∼0.01∘C/s), which activate classical nucleation and growth as well as pseudospinodal decomposition. These samples exhibit exceptional comprehensive mechanical properties, including an ultimate strength of approximately 1260 MPa and a total elongation of around 14 %. This investigation provides valuable guidance for designing novel heterogeneous precipitate microstructures by simply controlling the cooling rate, leading to significant enhancements in the mechanical properties of β-Ti alloys.

A novel formation mechanism: One-step synthesis of high-purity MAX phase bulk via enlarged reaction depth

The synthesis of high purity MAX phase bulk still faces a big challenge. In this study, we fabricated 98 vol% MAX phase bulk doped with Al2O3 nanoparticles through spark plasma sintering by using larger size TixAl1-x powders (particle size ∼100 μm) for the first time, in which 91 vol% Ti2AlN was the dominant component. The phase transition mechanism for Ti2AlN was deeply revealed by both experiments and theoretical calculations. Ti proportion of TixAl1-x powders played a key role in the formation of Ti2AlN, and increasing Ti proportion leaded to higher content of Ti2AlN. Both Al migration from TixAl1-x and TiN nanotwins generated by N vacancies could enlarge the reaction depth, resulting in fully transformation of larger size reactants and thus high purity MAX phase as obtained. Further, the transition model for the synthesis of Ti2AlN was accordingly proposed, which contained three stages and was additionally verified by experimental observations.

Probing the account of phase transition upon electrochemical cycling of the P2-Na0.67Ni0.15Fe0.2Mn0.65O2 layered oxide cathodes for sodium-ion batteries

Layered P2-Na0.67Ni0.15Fe0.2Mn0.65O2 (P2-NFM) cathode material has attracted great attention in sodium-ion batteries due to its high theoretical capacity, low cost, and environmental friendliness. However, P2-NFM exhibits irreversible phase transition and slip of transition metal layers in the high voltage range during charging process, leading to a gradually declined performance of the cathode material. It is therefore necessary to investigate the mechanism of phase transition of P2-NFM as well as the effect of phase transition on its performance. Herein, utilizing ex situ x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, the crystal structure and TM (transition-metal) bonding changes caused by phase transition are elucidated. It is found that P2-NFM is prone to undergo an irreversible P2-O2 phase transition at high voltage, causing changes in lattice parameters and rapid capacity decay. The irreversible phase transition is mainly due to he dynamic transformation of valence states of Fe and Ni in P2-NFM materials at high voltage. It is this process that results in irreversible fluctuations in the bond lengths between these elements and oxygen, consequently instigating interlayer slip within the material. Besides, the charge compensation mechanism of P2-NFM has been elucidated based on the study of its initial charging process. Results show that the charge compensation is mainly contributed by Ni and Fe in the high voltage range, while by a small amount of Mn in the low voltage range. It reveals the essential cause of the adverse phase transition of P2-NFM materials and points out the direction for improving the cycling stability of these layered oxide materials.

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Unraveling potential phase transition mechanism of NBT-based systems: From an interesting view to survey ferroelectric loops

As for assessing strain performances of Na0.5Bi0.5TiO3-based systems, the driving field level is a critical parameter. Currently, both current density and strain rate evaluation methods have been utilized to characterize the driving field. However, we find that some discrepancies indeed exist between these two evaluation methods, especially for the highly ergodic condition. By means of the typical ferroelectric theory, the initial analysis for discrepant current density and strain rate loops reveals that the relaxor-ferroelectric transition is likely to be a multi-step transition process. Dynamic dielectric loss/permittivity evolution further confirms the speculation and suggests that partial transition steps may be consisted of successive transition events. Ferroelectric and dielectric loops not only provide a fantastic view to unravel the multi-step relaxor-ferroelectric transition process, but also guides to regulate the strain appraisal system.

Crystal-Structure Matches in Solid-Solid Phase Transitions.

The exploration of solid-solid phase transition suffers from the uncertainty of how atoms in two crystal structures match. We devised a theoretical framework to describe and classify crystal-structure matches (CSM). Such description fully exploits the translational and rotational symmetries and is independent of the choice of supercells. This is enabled by the use of the Hermite normal form, an analog of reduced echelon form for integer matrices. With its help, exhausting all CSMs is made possible, which goes beyond the conventional optimization schemes. In an example study of the martensitic transformation of steel, our enumeration algorithm finds many candidate CSMs with lower strains than known mechanisms. Two long-sought CSMs accounting for the most commonly observed Kurdjumov-Sachs orientation relationship and the Nishiyama-Wassermann orientation relationship are unveiled. Given the comprehensiveness and efficiency, our enumeration scheme provide a promising strategy for solid-solid phase transition mechanism research.

Steering in-situ low-voltage phase transition from spinel to layered cathode for high-performance zinc-ion batteries

ZnV2O4, as a ternary transition metal oxides (TOMs), has garnered significant attention as a high-performance cathode for zinc-ion batteries (ZIBs) primarily due to its high theoretical capacity and abundance. However, its densely-packed lattice structure and strong coulomb interactions with the guest Zn2+ severely restrict the exposure of active sites and impede the diffusion kinetics. Herein, we propose an innovative in-situ low-voltage phase transition strategy and successfully trigger thorough phase transition of spinel-structured ZnV2O4 to layered-structured Zn3(OH)2V2O7⋅2H2O (ZnVOHNSs). In-depth mechanism analysis reveals that a thorough and efficient transition reaction necessitates meticulous control of the external driving force, reaction kinetics, and the reactant. The activated ZnVOHNSs with large lattice spacing and abundant oxygen vacancies provides an unobstructed pathway for accelerated ion diffusion and abundant exposed active sites for ions storage. Moreover, the inherent structure stability of ZnVOHNSs ensures exceptional reaction stability and reversibility during the Zn2+ intercalation/deintercalation process. Benefiting from these merits, the activated ZnVOHNSs cathode exhibits high reversible capacity and extraordinary rate capability (achieving 369 and 233 mAh g−1 at 0.1 and 20 A g−1, respectively), which exceeds most reported cathode materials in ZIBs. This work unveils the critical phase transition mechanism and offers insight into electrode design for advanced batteries.

Photonic Floquet Skin-Topological Effect.

Non-Hermitian skin effect and photonic topological edge states are of great interest in non-Hermitian physics and optics. However, the interplay between them is largely unexplored. Here, we propose and demonstrate experimentally the non-Hermitian skin effect constructed from the nonreciprocal flow of Floquet topological edge states, which can be dubbed "Floquet skin-topological effect." We first show the non-Hermitian skin effect can be induced by structured loss when the one-dimensional (1D) system is periodically driven. Next, based on a two-dimensional (2D) Floquet topological photonic lattice with structured loss, we investigate the interaction between the non-Hermiticity and the topological edge states. We observe that all the one-way edge states are imposed onto specific corners, featuring both the non-Hermitian skin effect and topological edge states. Furthermore, a topological switch for the skin-topological effect is presented by utilizing the phase-transition mechanism. Our experiment paves the way for realizing non-Hermitian topological effects in nonlinear and quantum regimes.

All laser direct writing process for temperature sensor based on graphene and silver

A highly sensitive temperature sensing array is prepared by all laser direct writing (LDW) method, using laser induced silver (LIS) as electrodes and laser induced graphene (LIG) as temperature sensing layer. A finite element analysis (FEA) photothermal model incorporating a phase transition mechanism is developed to investigate the relationship between laser parameters and LIG properties, providing guidance for laser processing parameters selection with laser power of 1–5 W and laser scanning speed (greater than 50 mm/s). The deviation of simulation and experimental data for widths and thickness of LIG are less than 5% and 9%, respectively. The electrical properties and temperature responsiveness of LIG are also studied. By changing the laser process parameters, the thickness of the LIG ablation grooves can be in the range of 30–120 μm and the resistivity of LIG can be regulated within the range of 0.031–67.2 Ω·m. The percentage temperature coefficient of resistance (TCR) is calculated as − 0.58%/°C. Furthermore, the FEA photothermal model is studied through experiments and simulations data regarding LIS, and the average deviation between experiment and simulation is less than 5%. The LIS sensing samples have a thickness of about 14 μm, an electrical resistivity of 0.0001–100 Ω·m is insensitive to temperature and pressure stimuli. Moreover, for a LIS-LIG based temperature sensing array, a correction factor is introduced to compensate for the LIG temperature sensing being disturbed by pressure stimuli, the temperature measurement difference is decreased from 11.2 to 2.6 °C, indicating good accuracy for temperature measurement.Graphical

Controllable transformed waves of a (3 + 1)-dimensional variable-coefficient Kadomtsev–Petviashvili equation in fluids or plasma

In this paper, we study the modulations of nonlinear transformed waves for a (3 + 1)-dimensional variable-coefficient Kadomtsev–Petviashvili equation in fluids or plasma. By virtue of the phase shift analysis, the shape-changed and unchanged transformed waves are investigated, which shows the inhomogeneity can restrain the time-varying property. The deformation of waves is determined by the phase difference between two wave components. In addition, the evolutions of parabolic transformed waves are illustrated via characteristic lines analysis. The interactions are further explored, which involve the long- and short-lived collisions. In particular, we discuss the dynamics of unidirectional and reciprocating molecular waves based on the velocity resonance condition, including the shape-changed and unchanged atoms. Different from previous results, certain new types of transformed molecular waves with shape-unchanged atoms are discovered. Our results indicate that the inhomogeneity can produce novel transformed waves and further facilitate the modulation of phase transition mechanism.