Integrated cryogenic optical microscopy and transport measurement system for spatiotemporal studies across phase transitions from 100 K to 400 K

Negative thermal expansion (NTE) is a counterintuitive phenomenon, in which materials undergo contraction as they are heated. ScF3, a well-known NTE material, has been reported to show NTE coefficients up to 1000 K. Under ambient conditions, ScF3 crystallizes in a cubic symmetry (Pm3̄m space group), the same as that in the ReO3-type structures. Crystal structure predictions (CSPs) show that at P = 1 GPa, a phase transition occurs in cubic ScF3 to form the rhombohedral phase (R3̄C space group). Quasi-harmonic approximation (QHA) calculations under high pressure conditions show that this new phase can show anisotropic NTE coefficients. The stability of this phase persists until 4 GPa. Beyond 4 GPa, the rhombohedral phase further undergoes a phase transition into an orthorhombic phase (Immm space group) with a non-corner-shared polyhedron network. This phase exhibits NTE along only one crystallographic axis, while the other two axes show no NTE response. On further increasing the pressure to 6 GPa, a trigonal-prismatic arrangement of ScF3 is obtained (R32 space group), which shows a reasonably better NTE than the previous phase due to the corner shared framework and remains stable until 9 GPa. All the phases show mechanical stability. Ab initio molecular dynamics (AIMD) simulations show that both the cubic and the rhombohedral phases show bond-length elongation as well as deviation in dihedral angle confirming their NTE.

Herein, a novel approach to create macroscale lower critical solution temperature (LCST) thermoresponsive hydrogels in a controlled manner using living cationic polymerization and a subsequent radical reaction is presented. By using a crosslinker capable of orthogonal reactions, 4-(vinyloxy)butyl methacrylate (VBM), which contains both vinyl ether and methacrylate moieties that react via cationic polymerization and radical reactions respectively, tremendous control over both the synthesis of the polymer structure as well as the hydrogel structure and its macroscale size and shape, by a post-polymerization UV light initiated radical reaction, is achieved. A series of random copolymers with the orthogonal crosslinker VBM, and LCST thermoresponsive monomers, methoxy ethyl vinyl ether (MOVE) or ethoxy ethyl vinyl ether (EOVE) or both, are synthesized. Introduction of VBM, even in small quantities, causes significant decreases in the observed phase transition temperatures for these thermoresponsive polymers and enables tuning of these temperatures. The hydrogels created from these polymers also exhibit clear LCST behavior with phase transition temperatures that are generally higher than for their corresponding polymers and over a wider temperature range. The use of this orthogonal reaction approach allows for control and design over both the polymer structure as well as that of the hydrogel.

Cold crystallization, an exothermic phase transition upon heating of a glassy state, is of interest in heat storage materials. While such behavior is common in polymers, small-molecule systems have also been investigated. Herein, we report a semiflexible macrocyclic compound composed of four silyl ether units and aromatic linkers that exhibits distinct cold crystallization. A key for the molecular design is semiflexible silyl ether units significantly affecting the macrocyclic shape. Differential scanning calorimetry revealed the formation of a glassy state by melt quenching, followed by exothermic crystallization. Powder X-ray diffraction indicated that the molecular conformation and packing in the crystals after cold crystallization are similar to those of solution-grown crystals. In contrast, a biphenylene-bridged macrocycle and a reference compound with a nonmacrocyclic structure did not show this behavior. These results suggest that a macrocyclic structure with suitable conformational mobility may help in the design of small molecular systems showing cold crystallization as heat storage materials.

Adaptive dynamic deformation has attracted growing attention because of its great significance for robots to adapt to the environment. However, designing a flexible smart material with reprogrammable and local programmable regulation for adaptive dynamic deformation in robotic systems is a substantial challenge. In nature, phase transitions are used to shape biological tissues, modulate growth shape through stiffness changes and provide growth momentum through fluid pressure. Inspired by this, we report a reprogrammable phase-transition composites that uses the stiffness change induced by reversible solid-liquid phase transition to program and regulate the material deformation actuated by reversible liquid-vapor phase transition, thereby achieving adaptive dynamic deformation in a controllable manner. By regulating the order of the two phase transitions, phase-transition composites can achieve not only reprogrammable deformation and local programmable deformation, but also rapid deformation and shape locking. We have developed a series of functional enhancements and applications using phase-transition composites, demonstrating the effectiveness of the composite phase-transition programmed deformation modulation mechanism. This mechanism enables robots to achieve reversible active deformation modulation and reprogrammable deformation modulation, opening a door for robotic systems with adaptive dynamic deformation.

Crystalline materials capable of responding to both heat and light stimuli offer unique opportunities for tunable dielectric behavior but have remained scarcely explored. Using a hydrogen-bond-guided supramolecular strategy, we synthesized a family of nitroprusside-based hybrids, (A)(NH4)[Fe(CN)5(NO)] (A = azetidinium (1), pyrrolidinium (2), piperidinium (3)), that exhibit reversible thermo-induced dielectric switching and intrinsic photoisomerization capability. Thermal, structural, and dielectric analyses reveal that all compounds exhibit a reversible thermally induced phase transition with dielectric switching driven by order-disorder transitions of polar cyclic ammonium cations. Compound 1 shows a one-step phase transition near 230 K, whereas 2 and 3 display multistep transitions with distinct pathways, with transition temperatures increasing systematically with cation size to 391 K. Variable-temperature single-crystal X-ray diffraction combined with molecular dynamics simulations elucidates that phase transitions and dielectric anomalies arise from sequential unlocking of rotational degrees of freedom within a hydrogen-bonded framework. Notably, the [Fe(CN)5(NO)]2- units preserve reversible photoinduced nitrosyl Fe-NO ↔ Fe-ON linkage isomerization, confirmed by IR spectra, suggesting the potential for light-driven dielectric modulation. This work establishes a clear structure-dynamics-property relationship linking organic cation dynamics in confined space to macroscopic dielectric behavior and highlights the promise of nitroprusside-based frameworks as dual thermo- and photoresponsive dielectric materials.

Strain-engineered upconversion nanoparticles with controlled Yb3+ doping exhibit power-tunable luminescence through lattice-strain-induced phase transitions. The strain modulation enables stepwise emission activation under varied excitation powers, achieving sequential information display. This single-wavelength excitation, power-gated approach provides a simple yet robust platform for dynamic and secure optical encryption.

Complex electromechanical systems (CEMS) integrate mechanics and electronics, but current models (complex network/bond graph) suffer from high computational costs and poor intuitive physical representation. Inspired by scattering parameter (S-parameter) models from radio frequency engineering, this paper innovatively proposes an S-parameter-based modeling framework for CEMS. First, a unified lumped-parameter modeling methodology is established for individual subsystems within CEMS. Next, the S-parameter characteristics of transmission channels between subsystems are analyzed. Based on this, load distribution and subsystem degradation equations are formulated. Furthermore, phase transition analysis during degradation is conducted by the degradation correlation length. By integrating system performance characterization equations, this study reveals underlying laws governing phase transitions of degradation structures and abrupt performance shifts during system degradation. Finally, the applicability of the proposed methodology is demonstrated through a numerical case involving an early warning radar system.

Ferroelastic phase transitions lead to the formation of ferroelastic twins, resulting in spatial inhomogeneities in the crystal structures and functional properties of ferroelastic materials. Despite the importance of such nanoscale twins in oxide heterostructures, their direct, non-invasive observation has relied on cumbersome and low-throughput techniques such as transmission electron microscopy and synchrotron X-ray diffraction, or been restricted to materials with coexistence of ferroelectric and ferroelastic states, by detecting the coupled ferroelectric order. In this study, the application of electron channeling contrast imaging (ECCI) in a scanning electron microscope for imaging ferroelastic domains in various oxide heterostructures is demonstrated. These include systems where ferroelasticity is coupled with critical functional properties such as ferroelectricity, magnetism and charge transport. The versatility of this imaging method is highlighted across different heterostructure geometries, from bare thin films to multilayers, achieving an impressive resolution of 6nm. ECCI presents a powerful approach for exploring the rich spectrum of ferroelasticity-coupled phenomena in oxide heterostructures.

ABSTRACT This research investigates J‐T refrigerators that employ nitrogen hydrocarbon zeotropic refrigerant mixtures and expansion capillary for producing low temperatures. Capillary tubes are frequently utilized as expansion devices within J‐T refrigerant systems. The refrigerant undergoes a phase transition subsequent to the flashing process within an expansion capillary. This study examines two mixtures capable of producing temperatures both below and above 123 K (at the capillary exit) to evaluate their flow characteristics within an expansion capillary. The simulation employs a homogeneous equilibrium approach. The numerical model developed in this study has been validated with the experimental results documented in existing literature. This study employs capillary tubes featuring diameters of 0.965 and 1.52 mm, with lengths varying from 1 to 2 m. It is estimated that the expected reduction in mass flow rate is between 20% and 30% as the capillary length increases from 1 to 2 m. Increasing the diameter from 0.965 to 1.52 mm is expected to yield a flow rate increase by a factor of 3.25. It is also calculated that the rise in temperature varies from 1 to 5 K as the capillary inlet pressure increases from 15 to 19 bar. It is calculated that gradient boosting regressor (GBR) and random forest (RF) exhibit a significant correlation between the actual and predicted mass flow rate values.

Optimizing the Rb modulation strategy in O3-type NaNi0.5Mn0.5O2 (NaNM) layered oxides addresses the practical challenges of phase transitions and slow ion diffusion, thereby unlocking near-theoretical capacity. Even with a minute 1% Rb doping, significant improvements in specific capacity and cycling stability are observed. The Na0.99Rb0.01Ni0.5Mn0.5O2 (NaNMR-1) sample exhibits a reversible capacity of 235.1 mAh g-1 at 0.2 C, maintaining 93.1% capacity retention after 100 cycles in a full cell configuration (NaNMR-1||HC). Theoretical calculations and comprehensive characterizations reveal that Rb decoration enhances Na+ transport channels and strengthens TM-O bonds, substantially reducing the energy barrier for ion migration and improving structural reversibility. This study underscores the potential of this approach to significantly enhance the cycle stability and specific capacity of O3-type layered oxide cathodes, promising for high-performance sodium-ion batteries.

The v = 5/2 fractional quantum Hall (FQH) state, as a special single-layer system with an even-denominator filling factor, serves as a promising platform for exploring exotic topological phases. In this study, we employ principal component analysis (PCA), an unsupervised machine learning technique, to investigate the evolution of many-body wavefunctions under particle-hole symmetry breaking. By introducing a model three-body potential to represent the mechanism of particle-hole symmetry breaking, we demonstrate that the ground state of the system transitions continuously between two distinct non-Abelian topological states, namely the Pfaffian and the anti-Pfaffian, as the strength and direction of the three-body term vary. Notably, the critical transition point corresponds to the pure Coulomb interaction, which preserves PH symmetry. Our results demonstrate that machine learning techniques, exemplified by PCA, provide a powerful and unbiased tool to identify and characterize topological phase transitions in FQH systems. Unlike traditional approaches that rely on predefined model wavefunctions, our method analyzes raw many-body wavefunctions directly, offering a model-independent framework applicable to a broader class of FQH systems undergoing topological transitions driven by symmetry breaking.

Artificial ground freezing technology empowering the construction of urban subway tunnels has been recognized as one of the most environmentally, friendly and efficient construction methods. However, ground frost heave and thaw settlement are the primary issues to be addressed in engineering practice, and anticipating these issues in advance will bring tremendous assistance to the construction of subway tunnels. Therefore, a three-dimensional thermodynamic coupling method is derived considering the phase transition process and the anisotropic characteristics of freeze-thaw soil. By calling the compiled incremental matrix equation in ABAQUS, the whole process simulation of the freezing construction of a plane skew connecting channel of Fuzhou Metro Line 5 is realized. The numerical simulation results indicate that the evolution process of the freezing temperature field and thawing temperature field in numerical simulation is consistent with the theoretical design, and the natural thawing time is about 1.5 times of the positive freezing time. Besides, the evolution law of ground surface displacement in numerical simulation is consistent with the field measurement, and their displacement-time curves conform to the power function fitting relationship, and the correlation coefficients are all greater than 0.9. After freezing for 45 days, the ground surface frost heave displacement at the midpoint of the connecting channel in numerical simulation is 52.43mm, while the measured value on site is 49.58mm, with an error of only 2.85mm. After thawing for 68 days, the ground surface thaw settlement displacement at the midpoint of the connecting channel in numerical simulation is - 23.77mm, while the measured value on site is - 24.02mm, with an error of only 0.25mm. All these indicate the accuracy of the established numerical simulation prediction method.

Noise is inevitable in realistic quantum circuits. It arises randomly in space. Inspired by the spatial nonuniformity of the noise, we investigate the effects of spatial modulation on quantum phase transitions in a hybrid random Clifford circuit with a mixed initial state. As an efficient observable for extracting quantum entanglement in mixed states, we employ many-body negativity. The behavior of the many-body negativity well characterizes the presence of the phase transitions and its criticality. We find the effect of spatial nonuniformity in measurement probability on the phase transition. The criticality of the phase transition changes from that of uniform probability, which is elucidated by the argument of the Harris criterion. The critical correlation length exponent ν changes from ν < 2 for uniform probability to ν > 2 for spatially modulated probability. We further investigate a setting where a two-site random Clifford gate becomes spatially (quasi)modulated. We find that the modulation induces a phase transition, leading to a different pure phase where a short-range quantum entanglement remains.

Abstract The interdecadal changes of climate under accelerating global warming have profound impacts on various countries in the northern hemisphere (NH). Using ERA5 reanalysis data, interdecadal changes of Rossby wave energy propagation (RWEP) pathways and their impacts are examined in the present work. Results demonstrate that the NH-means of 500hPa geopotential height anomalies vary with large interdecadal trends that keep in step with global warming, exhibiting a negative-to-positive phase transition from Period-I (1950/51-1996/97) to Period-II (1997/98-2024/25). Pronounced interdecadal eastward-shifts occur systematically in interannual variabilities of apparent wave sources, which correspondingly result in large interdecadal changes of RWEP pathways in regions from northeast Atlantic to Eurasia and from northeast Pacific to north America. Significant interannual surface air temperature anomalies with extremes about ±5°C are induced by circulation variations in regions around these pathways, facilitating possible occurrences of climate extremes in Eurasia and North America with different spatial patterns between Period-II and Period-I.

Abstract A systematic investigation of the optical emission and absorption properties in nitrogen‐implanted Ga 2 O 3 in correlation with its polymorphic stability controlled by dynamic defect annealing is undertaken. It is demonstrated that dynamic annealing processes, determined by the irradiation temperatures, significantly influence both disorder accumulation and phase transformations in β‐Ga 2 O 3 , in turn, leading to a modulation of the absorption and emission properties of the implanted material. Specifically, room‐temperature implantation induces β‐to‐γ phase transitions, accompanied by an enhancement of the characteristic green luminescence (GL) band. In contrast, implantation at elevated temperatures suppresses γ‐phase formation and promotes the emergence of strong red luminescence (RL) emission. The results are interpreted within the framework of competing effects between defects generated during the β‐to‐γ phase transformation and the incorporation of implanted nitrogen atoms. The presented findings contribute to a deeper understanding of dopant‐defect interactions in Ga 2 O 3 as well as modulation of the optical properties of its polymorphs.

Abstract The systematic uncertainties of chemical freeze-out fits at SIS100 energies (Au+Au reactions at $$\sqrt{s_{NN}}=3-5$$ s NN = 3 - 5 GeV) are studied using UrQMD simulations. Although hadron production in UrQMD does not occur on a sharp chemical freeze-out hyper-surface, the extracted fit quality is shown to be very good. The extracted chemical parameters depend on the selected hadron species as well as the underlying equation of state (EoS) of the matter. Including light nuclei and anti-protons in the fit increases the expected freeze-out temperature, while a stiffer EoS increases the obtained chemical potential. Similarly, the baryon densities extracted by the thermal fits depend on the choice of hadrons as well as the underlying equation of state. These results are important for the upcoming CBM@FAIR physics program and highlight that a degree of caution is advised when one relates the chemical freeze-out curve to features on the QCD phase diagram like the critical endpoint or a possible phase transition.

Abstract Two-dimensional zinc sulfide (ZnS) nanosheets hold significant promise for next-generation flexible optoelectronics and nano-devices, yet the potential of graphenylene-derived porous architectures and their strain-driven structural dynamics remains unexplored. Motivated by this gap, we employ density-functional tight-binding simulations to investigate novel ZnS nanosheet phases inspired by graphenylene-like (G-like) and the GME nanoporous crystal. We demonstrate the stabilization of both a planar bilayer G-like phase (G-2) and a metastable monolayer cage-like GME phase (GME-1) from the same atomic structure, governed by distinct lattice parameter ranges. Crucially, we identify and characterize reversible, strain-mediated phase transitions between these morphologies, which occur under a biaxial tensile strain of 6.5%–7% (corresponding to a lattice parameter range of 10.30–10.35 Å) relative to the GME-1 equilibrium structure. This transition, enabled by a minimal energy barrier of ∼0.1 eV/ZnS, induces a substantial bandgap modulation of ∼1 eV, directly coupling mechanical deformation to electronic restructuring. Both phases exhibit robust dynamical, thermal (≤500 K), and mechanical stability. This discovery of morphology-dependent stability and reversible, strain-tunable phase transitions with coupled electronic properties in porous ZnS nanosheets paves the way for their application in advanced optomechanical switches, nanosensors, UV photodetectors, and mechanical metamaterials.

Ferroelastics have attracted considerable attention due to their promising applications in energy conversion, sensing, and shape memory devices. The integration of ferroelasticity with additional physical properties, such as thermochromism and semiconductivity, in a single material offers new opportunities for advanced applications, yet significant challenges. Here, we report a bismuth-based organic-inorganic hybrid ferroelastic semiconductor, [HPym]3[H2Pym][Bi2Br11] (Pym = pyrimidine), which exhibits a narrow band gap of 1.62 eV. It undergoes a reversible ferroelastic phase transition with Aizu notation of 4/mF2/m at 282 K. More importantly, the phase transition is accompanied by a reversible thermochromic behavior, characterized by a color change from red to yellow. The coexistence of ferroelasticity, thermochromism, and semiconductivity in [HPym]3[H2Pym][Bi2Br11] highlights its potential for practical applications.

Role of quantum state texture in probing resource theories and quantum phase transitions