Transition Mechanism Research Articles

Bonding Transition Mechanism in Invar Alloy Induced by Noncollinear Magnetic Disorder: DFT+U Insights

Bonding Transition Mechanism in Invar Alloy Induced by Noncollinear Magnetic Disorder: DFT+<i>U</i> Insights

Optical imaging of the stochastic nucleation kinetics and intrinsic activation energy of single spin-crossover nanoparticles

Cooperative spin crossover (SCO) compounds are one of the most promising molecular bistable solids due to their intriguing thermal hysteresis phenomena around room temperature. It is well known that hysteresis is an essential kinetic effect, however, accurate assessment of the spin transition kinetics of SCO nanomaterials remains scarce. Herein, we developed a thermal-optical methodology to image the thermally induced spin transition kinetics of single SCO nanoparticles in a quantitative, repeatable, and high-throughput manner. Single-particle measurement revealed an intrinsic nucleation-dominated spin transition mechanism, where a highly stochastic nucleation process was clearly observed during the repeatable measurements. By quantifying the dependence of nucleation time on temperature, the activation energy barriers for nucleation were further extracted at a single particle level. Based on this foundation, the high throughput of the optical imaging not only contributed to uncovering the significant nanoparticle-to-nanoparticle heterogeneity, with implications for a negative correlation between apparent activation energy barriers for nucleation and size of the SCO nanoparticles, but also facilitated identifying a minority with high activation energy at least twice the average value. The extraordinary performance was then attributed to the fewer defects within their structures, as confirmed by further results from the in situ creation of defects by thermal ablation, thereby setting the lower limit for the intrinsic activation energy of ideal SCO crystals and promising their potential for future applications in high-performance molecular devices.

Control of roughness-induced transition in supersonic flows by local wall heating strips

Isolated-roughness-induced transitions controlled by local wall heating strips are studied via direct numerical simulation and BiGlobal linear stability analysis. The transition mechanisms are studied first with different wall temperatures. The separated shear layer–counter-rotating vortex system is found to be the main source for transitions. Symmetric and antisymmetric modes are observed in the wake, and the former is dominant. The local wall heating strip can delay the transition, and this effect is enhanced with higher heating temperature, wider strip and a combination of upstream and downstream control strips. The upstream strip lifts up the inlet flow and weakens the wake system in an indirect manner. The antisymmetric mode gradually vanishes, while the symmetric mode always exists but becomes weaker. The downstream strip exhibits a more effective transition delay by directly weakening the separated shear layer and vortex system in the wake. Vorticity transport analysis suggests that the downstream strip increases dissipation for streamwise vorticity and transfers it into wall-normal and spanwise vorticity. BiGlobal analyses indicate that the downstream strip shows less influence on the peak growth rate of the symmetric mode but significantly shrinks its unstable region. Analyses of the disturbance energy production indicate that the upstream strip wakens the wall-normal and spanwise shear at the same time, but the downstream strip mainly wakens the wall-normal one. More simulations are performed with different roughness heights, point-source disturbance and different roughness shapes. The results show that the current method remains effective enough in delaying transitions at a wide range of conditions.

Bonding states underpinning structural transitions in IrTe2 observed with micro-ARPES

Competing interactions in low-dimensional materials can produce nearly degenerate electronic and structural phases. We investigate structural phase transitions in layered IrTe2 for which a number of potential transition mechanisms have been postulated. The spatial coexistence of multiple phases on the micron scale has prevented a detailed analysis of the electronic structure. By exploiting micro-angle-resolved photoemission spectroscopy obtained with synchrotron radiation we extract the electronic structure of the multiple structural phases in IrTe2 in order to address the mechanism underlying the phase transitions. We find direct evidence of lowered energy states that appear in the low-temperature phases, states previously predicted by calculations and extended here. Our results validate a proposed scenario of bonding and antibonding states as the driver of the phase transitions. Published by the American Physical Society 2024

Laser-based approach to measure small nuclear cross sections in plasma

We demonstrate an approach successfully measuring very small nuclear isomeric excitation cross sections (on the order of 10 to 100 picobarns) via laser-cluster interaction. The interaction between an intense laser pulse and Kr atomic clusters generates a high-temperature and high-density plasma ball in which nuclear excitations are facilitated by inelastic electron scattering. The electron temperature reaches several hundred keV (corresponding to 10[Formula: see text] K), similar to a stellar environment. The very small nuclear excitation cross sections are extremely challenging to measure otherwise, for example using traditional accelerator-based approaches. Our method opens a broad avenue of measuring small nuclear cross sections and holds promise for advancing understanding of nuclear transition mechanisms and exploring pathways in the evolutionary dynamics of elements within stellar environments.

Low temperature exciton lifetime enhancement of MAPbBr3 studied by broadband terahertz spectroscopy

Over the past few years, lead halide perovskites have demonstrated significant potential in the field of solar cells, light-emitting diodes, and field-effect transistors. We investigated the transient photoconductivity and temperature-induced phase transitions in MAPbBr3 thin films, using ultrabroadband optical pump-terahertz probe spectroscopy with varying excitation fluences and temperature conditions. As the temperature drops from 293 to 123 K, MAPbBr3 undergoes two phase transitions, resulting in a significant extension of exciton lifetime in the tetragonal phase near 150 K, where MAPbBr3 exhibits a longer exciton lifetime. Our research contributes to a better understanding of the temperature-induced phase transition mechanism of MAPbBr3, enhancing its potential applications in optoelectronic devices.

Room Temperature Phase Transition and Luminescence Behavior of a Novel Metal‐Free Ionic Crystal [C7H16NO][ClO4

AbstractMetal‐free ionic crystals have attracted tremendous attention for their environmental friendliness, biocompatibility, easy fabrication and structural variability. Herein, a metal‐free ionic crystal [C7H16NO][ClO4] ([C7H16NO]=1‐methyl‐4‐piperidinemethanol) with a dielectric transition at room temperature was designed and constructed. Differential scanning calorimetry (DSC) proved that there exists a reversible phase transition near room temperature at 304 K, accompanied with switchable dielectric behaviors between the low and high dielectric states. The single crystal structure show that the mechanism of such structural phase transition mainly results from the dynamic motion of perchlorate anions. The compound is further shown to exhibit remarkable luminescent properties, characterized by a prolonged lifetime of 18.6 ns. This work offers valuable insights into the construction of room temperature phase‐transition ionic crystals involved with dielectric switching and blue luminescence properties.

Pattern phase transition of spin particle lattice system

To better understand the pattern phase transition of both physical and biological systems, we investigate a two-dimensional spin particle lattice system using statistical mechanics methods together with XY model governed by Hamiltonian equations of motion. By tweaking the coupling strength and the intensity of the generalization field, we observe phase transitions among four patterns of spin particles, i.e., vortex, ferromagnet, worm and anti-ferromagnet. In addition, we analyze the effect of space boundaries on the formations of vortex and worm. Considering the inherent dynamics of individual particles, we revealed the forming mechanism of such phase transitions, which provides a new perspective for understanding the emergence of phase transition of spin particles systems.

Microscopic mechanism of water-assisted diffusional phase transitions in inorganic metal halide perovskites.

The stability of perovskite materials is profoundly influenced by the presence of moisture in the surrounding environment. While it is well-established that water triggers and accelerates the black-yellow phase transition, leading to the degradation of the photovoltaic properties of perovskites, the underlying microscopic mechanism remains elusive. In this study, we employ classical molecular dynamics simulations to examine the role of water molecules in the yellow-black phase transition in a typical inorganic metal halide perovskite, CsPbI3. We have demonstrated, through interfacial energy calculations and classical nucleation theory, that the phase transition necessitates a crystal-amorphous-crystal two-step pathway rather than the conventional crystal-crystal mechanism. Simulations for CsPbI3 nanowires show that water molecules in the air can enter the amorphous interface between the black and yellow regions. The phase transition rate markedly increases with the influx of interfacial water molecules, which enhance ion diffusivity by reducing the diffusion barrier, thereby expediting the yellow-black phase transition in CsPbI3. We propose a general mechanism through which solvent molecules can greatly facilitate phase transitions that otherwise have prohibitively high transition energies.

Financial mechanisms for energy transitions: review article

PurposeThe transition from fossil fuel-based energy systems to renewable energy sources, commonly referred to as the energy transition, is essential for combating climate change. However, comprehensive studies that thoroughly examine the financial mechanisms involved in this process are lacking. Despite the availability of various financial tools, there is a notable absence of extensive research that synthesizes and categorizes these mechanisms into broad groups.Design/methodology/approachA systematic literature review is used to explore a comprehensive framework for financial mechanisms related to the energy transition and their application across six stages of the process.FindingsThe framework of financial mechanisms for energy transition encompasses these six factors: public financing mechanisms, private financing mechanisms, market-based mechanisms, innovative financing mechanisms, risk mitigation instruments and institutional support and capacity building.Originality/valueThis is the first study that thoroughly reviewed the financial mechanisms involved in the energy transition process.

Polymorphism in Type-II Dirac Semimetal WSi2 under Pressure: Structural, Mechanical, and Electronic Insights.

The type-II Dirac candidate semimetal WSi2 is a promising candidate for electronic devices, quantum computing, and topological materials research, owing its distinct electronic structure and superior mechanical properties. Here, we synthesized high-quality WSi2 materials and systematically investigated their compressive behavior, and structural and electronic properties under high pressure using in-situ high pressure experiments, complemented by first-principles calculations. The results confirms that WSi2 has the properties of a type-II Dirac semimetal. Our results demonstrate that WSi2 maintains structural stability under high pressure but undergoes an electronic phase transition from a semimetal to a metal around 40 GPa. Additionally, the mechanical hardness softens discontinuously at this pressure. The structural stability of WSi2 under high pressure is attributed to the strong hybridization of Si-3p and W-5d electrons, the rigid crystal lattice, and the adaptable electronic structure. The pressure-induced electronic phase transition and softening are primarily governed by the energy band reconstruction and W-5d orbitals. This study provides valuable insights into the high-pressure behavior of type-II Dirac semimetal, highlighting their potential for advanced applications in electronic devices and topological quantum computing under extreme conditions by elucidating their structural stability and electronic phase transition mechanisms.

Capabilities and limitations of smoothed particle hydrodynamics for the simulation of two‐phase flow instabilities

AbstractSmoothed particle hydrodynamics (SPH) is a mesh‐free, Lagrangian particle‐based method that is able to simulate multiphase flows in an economical manner. However, its ability to capture the flow regimes and regime transitions in two phase (liquid‐gas) internal flows, such as pipe or channel flows is not yet generally established. To address this lack in understanding, we first examine a laminar rising bubble case in order to evaluate the fluid‐fluid interface representation and transient interface evolution by the solver. With a focus towards the transition mechanism from a stratified flow regime to a slug flow regime, we investigate the Kelvin–Helmholtz instability (KHI) both qualitatively and quantitatively, initially focusing on a low density ratio () and then extending it to a high density ratio (). For the low density ratio, we conduct an analysis of the temporal evolution and demonstrate that the SPH solver captures the initial exponential growth in qualitative agreement with inviscid linear stability theory (LST) and reference numerical data for shear‐dominated flow with Richardson number . By conducting eight additional simulations for various for the high density ratio, we demonstrate that the numerically obtained parameter value for instability is around , which is in reasonable agreement with the theoretically expected value of . Based on the SPH results obtained for the range , we suggest a simple parameterization of the reduction of the effective growth rate proportional to .

Phason and Amplitudon Modes in K3Na(SeO4)2 Crystal

For the first time, the Nambu–Goldstone optical mode has been observed in ferroelastic crystals. The amplitudon and phason modes were identified in the Raman spectra of the K3Na(SeO4)2 (KNSe) crystal. We discuss the occurrence of such lattice vibration with regard to the possible presence of an incommensurate (IC) phase. The potential scenario of the dynamics of the SO4 tetrahedron leading to the appearance of an IC phase, accompanied by critical temperature behavior of two external vibrations of Ag symmetry, is given together with the molecular mechanism of the phase transitions in the material studied. The effect of the spatial reorganization of the crystal lattice associated with the ferroelastic domains of the KNSe crystal of W and W′ types is also discussed. We show that the emergence of such a domain structure may also be a source of incommensurability.

Lung cancer and pulmonary tuberculosis: key features of molecular mechanisms of concomitant disease

Lung cancer and pulmonary tuberculosis have long been significant problems for global health, occupying leading positions in terms of morbidity and mortality in both developed and developing countries. Numerous clinical and experimental studies have allowed to get knowledge of the mechanisms of development of these pathological processes individually, the impact of diseases on the macroorganism, and various options of treatment. According to population studies, the interaction between these two processes is undeniable – both active tuberculosis and post-tuberculosis changes are equally risk factors for the development of neoplastic processes, and malignant tumors create favorable conditions and predispositions for the development of mycobacterial infection. However, the mechanisms of interaction between these two diseases in concomitant cases remain opened and insufficiently studied. This literature review provides a detailed description of the variants of lung cancer and pulmonary tuberculosis combinations, the pathophysiological basis of the interaction between infectious and neoplastic processes: modulation of the immune response by M. tuberculosis and lung tumor; oncogenic signaling pathways activated by tuberculosis infection; mechanisms of epithelial-mesenchymal transition in post-tuberculosis scar changes and its role in the formation of so-called "scarcinoma"; the relationship between tumor-mediated and tuberculosis-associated immunosuppression; the role of the PD-1: PD-L signaling pathway, and the influence of modern types of anti-tumor immunotherapy on the course of these pathological processes. The final part of the review presents our own data from experimental studies on the combination of cancer and tuberculosis in a laboratory model, identifying promising directions for further research on this issue.

Phase transitions of ice VIII-VII-X: A potential energy landscape perspective

Water ice, an archetypal molecular system, exhibits a complex phase diagram characterized by numerous phase transitions under varying pressure-temperature conditions. However, it remains a significant challenge to theoretical modeling of these transitions owing to the high dimensionality in representing the potential energy landscapes (PEL) of ice crystalline phases. In an attempt to deeply understand the mechanisms of phase transitions between ice VII, VIII, and X, a graph-based stationary-point network was employed to simplify the representation of the PEL and locally constructed the PEL of ice at different pressures by our developed high-index saddle dynamic scheme. The stationary-point networks at 40 and 80 GPa indicate a pronounced flattened PEL of ice over a wide range of pressure (up to at least 80 GPa), where multiple structures (i.e., local minima) are energetically degenerate with phase VIII and separated by low-energy barriers (∼10 meV/atom at 40 GPa). These features indicate the disordered VII phase is more favorable at finite temperatures, in agreement with previous experimental observations. Additionally, we demonstrated that the PEL topology undergoes a fundamental alteration at higher pressures, with a single funnel emerging at 120 GPa, facilitating the crystallization of phase X. This work serves as a proof of concept for using the stationary-point network to explicitly represent the PEL, highlighting their potential in elucidating complex phase transitions. Published by the American Physical Society 2024

Improving Mechanisms for an Equitable Transition to Low-Carbon Development within the BRICS Framework

Nowadays transformational changes are going together with the need to address global environmental and climatic challenges. The BRICS member countries realize the need for a fair energy transition to lowcarbon development both within the association and globally.Aim. The objective of the research is to highlight the priority areas that BRICS member countries need to focus on to ensure an equitable and cost-effective transition to low-carbon development at the global level.Tasks. In order to achieve the objective of the study, it is necessary to analyze the components of the BRICS equitable low-carbon development agenda as well as its applicability at the global level.Methods. The research was conducted using the method of systematic analysis of a wide range of academic and empirical sources. The author adheres to a systematic scientific approach.Results. Through the analysis of key initiatives of the BRICS member countries, including legislative ones, five priority areas on which the BRICS needs to focus on to ensure a fair energy transition at the global scale are identified: removing discriminatory measures in multilateral trade, achieving food security and economic growth, facilitating non-discriminatory access to technology, promoting environment and climate cooperation, and enhancing the human resource potential of the energy sector.Conclusions. The author concludes by noting that such a BRICS sustainable development agenda is capable of initiating energy transition processes on a global scale.

Study on the fluid-solid transition mechanism of natural hydraulic lime pastes: Consider the water to binder ratio and polycarboxylate superplasticizer

Natural hydraulic lime (NHL) is used as a grouting material in the restoration of ancient buildings, the formation and evolution of its early workability are crucial for the reliability of the restoration effects. This paper conducts an in-depth study on the effects of water to binder (w/b) ratio and polycarboxylate superplasticizer (SP) dosage on the viscoelastic properties of fluid-solid transition process in NHL paste through tests on the fluidity, rheological characteristics, micro-rheology, hydration heat release, and early phase composition. The results show that the fluidity of NHL paste significantly increases with increasing w/b ratio and SP dosage, while its yield stress and plastic viscosity show downward trend, and it has shear thinning characteristics. In the initial stage, elevated w/b ratio leads to the significant reduction in both macroscopic viscosity index (MVI) and elastic index (EI) of NHL paste, along with delayed rapid increases, the effect is even more pronounced by adding SP. High w/b ratio or adding SP are able to enhance the dispersed state of solid particle in NHL pastes, the viscoelastic transition point of NHL paste is delayed and the viscoelastic transition time is prolonged. Increasing the w/b ratio and adding SP both inhibit the early dissolution and hydration of NHL paste, affecting the fluid-solid transition process. Overall, as the spatial network gradually develops by the solid particles dissolve and continue to hydrate, NHL paste undergoes a transition from a viscous fluid to an elastic semi-fluid state, exhibiting low strength and noticeable plasticity characteristics. With further hydration, NHL paste initiates consolidation and hardening processes, progressively transforming from a plastic semi-fluid into hardened paste.

Phase transition mechanism and property prediction of hafnium oxide-based antiferroelectric materials revealed by artificial intelligence

Phase transition mechanism and property prediction of hafnium oxide-based antiferroelectric materials revealed by artificial intelligence

Plastic evolution and phase transition mechanisms in γ-TiAl nano polycrystal by a molecular dynamics simulation

γ-TiAl based alloys are widely regarded as one important high-temperature structural material, however the deformation behaviors are still not clearly clarified. The microscopic plastic deformation and phase transition of γ-TiAl nano polycrystals under compression are investigated by molecular dynamics simulations. The results show that the initial plasticity is dominated by slip of partial dislocations whose continuous formation and secondary slip on the same slip plane result in the generation and disappearance of intrinsic stacking faults (ISFs). At the strain of about 0.2, a continuous structure transformation of “ISF → ESF → TB” is observed, during which the interaction between different ISFs causes the atomic misalignment corresponding to the change in atomic stacking order near ISF. As the compressive strain exceeds 0.2, the FCC-to-BCC phase transition occurs within polycrystals due to the high Mises stress, the high stress level within grains facilitates the expansion of BCC phase from initial FCC phase, and the newly formed BCC phase maintains the atomic-arrangement orderliness of original phase. The interface between FCC and BCC phases obeys the low-energy Kurdjumov-Sachs orientation relationship. This work is helpful for better understanding the atomic-scale deformation behaviors and provides a theoretical guidance for designing high-performance alloy materials.

The study of micellar transitions in mixed systems of dibranched cationic/nonionic fluorinated surfactants using various physicochemical methods

AbstractIn this study, a new method was introduced to induce micellar transitions by using vesicles formed from mixed surfactants, which offer enhanced stability. Different physicochemical analysis methods were used to study the transition mechanism and the aggregation behavior of the mixed aqueous system composed of the double‐chain cationic didodecyldimethylammonium bromide (DDAB) and a single‐chain nonionic fluorinated surfactant undecafluoro n‐pentyl decaoxyethylene ether (C5F11(EO)10), by varying the fraction of DDAB, then the total surfactant concentration of DDAB/C5F11(EO)10 mixed system at XDDAB = 0.9. The obtained results indicated that the addition of the fluorinated surfactant C5F11(EO)10 to the mixed system resulted in a reduction of the surface tension (γ) and a decrease in the Electrical conductivity (K). Furthermore, even at high total concentrations of the mixed system, the conductivity and charge density at the surface remained stable. As XDDAB values increased, a higher degree of dissociation (α) was observed, along with negative values in the thermodynamic parameters of micellization (Δ, Δ, and Δ), confirming the transition from micelles to vesicles. The dynamic light scattering (DLS) analysis revealed the formation of two stable types of aggregates at both low and high concentrations, as supported by the zeta potential (ζ). Upon increasing the concentration of surfactants, UV–Vis absorption measurements indicated that small spherical micelles grow into large multilamellar vesicles, as evidenced by an increase in turbidity and confirmed transmission electron microscopy images.