Mechanism Of Phase Transition Research Articles

Pressure Induced Disorder-Order Phase Transitions in the Al4Cr Phases

An ordered ω-Al4Cr phase synthesized recently by a high-pressure sintering (HPS) approach was calculated to be stable by density function theory (DFT), implying that high pressure can accelerate the disorder-order phase transitions. The structural building units of the ω-Al4Cr phase as well as the non-stoichiometric disordered ε-Al4Cr and μ-Al4Cr phases have been analyzed by the topological “nanocluster” method in order to explore the structural relations among these phases. Both the ε-and μ-Al4Cr phases contain the typical Macky or pseudo-Macky cluster, and their centered positions were all occupied by Cr atoms, which all occupy the high-symmetry Wyckoff positions. The mechanism of the pressure-induced disorder-order phase transitions from the ε-/μ-Al4Cr to the ω-Al4Cr phase has been analyzed. and the related peritectic and eutectoid reactions have been re-evaluated. All results suggest that the stable ω-Al4Cr phase are transformed from the μ-Al4Cr phase by the eutectoid reaction that is accelerated by high-pressure conditions, whereas the ε-Al4Cr phase should form by the peritectic reaction.

Research on Monocrystalline Silicon Micro-Nano Structures Irradiated by Femtosecond Laser.

Femtosecond (fs) laser processing has received great attention for preparing novel micro-nano structures and functional materials. However, the induction mechanism of the micro-nano structures induced by fs lasers still needs to be explored. In this work, the laser-induced periodic surface structure (LIPSS) of monocrystalline silicon (Si) under fs laser irradiation is investigated. Three different layers named amorphous silicon (a-Si) layer, transition layer, and unaffected Si layer are observed after laser irradiation. The a-Si layer on the surface is generated by the resolidification of melting materials. The unaffected Si layer is not affected by laser irradiation and maintains the initial atomic structure. The transition layer consisting of a-Si and unaffected Si layers was observed under the irradiated subsurface. The phase transition mechanism of Si irradiated by fs laser is “amorphous transition”, with the absence of other crystal structures. A numerical model is established to describe the fs laser-Si interaction to characterize the electronic (lattice) dynamics of the LIPSS formation. The obtained results contribute to the understanding of fs laser processing of Si at the atomic scale as well as broaden the application prospects of fs laser for treating other semiconductor materials.

Phase-Transition Mechanism and the Atomic Interface Structure of Brookite to Rutile: Resolving from Machine-Learning Global Pathway Sampling

Phase-Transition Mechanism and the Atomic Interface Structure of Brookite to Rutile: Resolving from Machine-Learning Global Pathway Sampling

Operando X-Ray Diffraction Nanoimaging of Advanced Cathodes

Techniques capable of probing active materials in situ are increasingly needed to link cell performance data with nanostructural evolution inside functional devices. Rapid improvements in spatial and temporal resolution of X-ray nanomicroscopy and high-energy diffraction facilitated by new 4th-gen synchrotrons offer a powerful platform for investigating phase transitions inside advanced cathode materials. We show how the latest methodologies can be used to evaluate the mechanism of phase transitions at the nanoscale, linked to degradation processes inside commercially relevant cells."Single crystal" cathode active materials have garnered incredible academic and industrial interest in the past several years. Despite extensive electrochemical performance validation, there remain very few tools capable of evaluating the quality and consistency of these materials. Scanning X-ray nanodiffraction microscopy reveals the hidden microstructure and defects inside nominally single crystal cathode particles established during their fabrication. In situ nanodiffraction imaging provides further insight towards the link between this microstructure and functional properties such as high voltage stability inside individual crystallites during cycling.

Thermoresponsive Liposomes for Photo-Triggered Release of Hypericin Cyclodextrin Inclusion Complex for Efficient Antimicrobial Photodynamic Therapy.

Antimicrobial strategies with high efficacy against bacterial infections are urgently needed. The development of effective therapies to control bacterial infections is still a challenge. Herein, near-infrared (NIR)-activated thermosensitive liposomes (TSL) were loaded with the NIR-dye 1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide (DiR) and the water-soluble hypericin (Hyp) β-cyclodextrin inclusion complex (Hyp-βCD). DiR and Hyp-βCD loaded thermosensitive liposomes (DHβCD-TSL) are functionalized for photothermal triggered release and synergistic photodynamic therapy to eliminate the gram-positive Staphylococcus saprophyticus. The dually active liposomes allow the production of heat and singlet oxygen species with the help of DiR and Hyp, respectively. The elevated temperature, generated by the NIR irradiation, irreversibly damages the bacterial membrane, increases the permeation, and melts the liposomes via a phase-transition mechanism, which allows the release of the Hyp-βCD complex. The photodynamic effect of Hyp-βCD eradicates the bacterial cells owing to its toxic oxygen species production. DHβCD-TSL measured the size of 130 nm with an adequate encapsulation efficiency of 81.3% of Hyp-βCD. They exhibited a phase transition temperature of 42.3 °C, while they remained stable at 37 °C, and 44% of Hyp-βCD was released after NIR irradiation (T > 47 °C). The bacterial viability dropped significantly after the synergistic treatment (>4 log10), indicating that the NIR-activated TSL have immense therapeutic potential to enhance the antibacterial efficacy. The liposomes showed good biocompatibility, which was confirmed by the cellular viability of mouse fibroblasts (L929).

Kibble-Zurek mechanism for nonequilibrium phase transitions in driven systems with quenched disorder

We show that the Kibble-Zurek mechanism applies to nonequilibrium phase transitions found in driven assemblies of superconducting vortices and colloids moving over quenched disorder where a transition occurs from a plastic disordered flowing state to a moving anisotropic crystal. We measure the density of topological defects as a function of quench rate through the nonequilibrium phase transition, and find that on the ordered side of the transition, the topological defect density ρd scales as a power law, {rho }_{{{{{{{{rm{d}}}}}}}}}propto 1/{t}_{{{{{{{{rm{q}}}}}}}}}^{beta }, where tq is the quench time duration, consistent with the Kibble-Zurek mechanism. We show that scaling with the same exponent holds for varied strengths of quenched disorder and that the exponents fall in the directed percolation universality class. Our results suggest that the Kibble-Zurek mechanism can be applied to the broader class of systems that exhibit absorbing phase transitions.

Nb-doped VO2 single crystal microtube arrays

Nb-doped VO2 microtube arrays were fabricated by a thermal oxidation process of V–Nb alloy foils in air. The Nb-doped VO2 microtubes are featured with the rod-like, hollow, and rectangular cross-sectional single crystal, where arrays aligned nearly vertically on the surface of a Nb-doped V2O5 substrate. Phase transition examinations demonstrate that Nb doping can decrease the metal-insulator transition temperatures of VO2 by approximately 15 °C/at. % Nb, which reaches the highest decrease efficiency for metal-insulator transition temperatures of Nb-doped VO2. The phase transition route and mechanism of Nb-doped VO2 microtube arrays are revealed.

Multimodal Gas Sensor Detecting Hydroxyl Groups with Phase Transition Based on Eco‐Friendly Lead‐Free Metal Halides (Adv. Funct. Mater. 28/2022)

Multimodal Gas Sensors In article number 2202207, Hyung Woo Lee, Han Seul Kim, Jin Woo Choi, and co-workers study the mechanism of hydroxyl-induced reversible phase transition of Cs3Cu2I5 and CsCu2I3 and fabricate electrical-optical responsible multimodal gas sensors. The hydroxyl sensors show optical red-shifted emission and electrical resistance increment in 5s and 1 min, respectively. The sensor can be repeatably operated under room temperature with a low operation voltage of 1V with high stability over 1 year.

Structural and elastic behaviour of aragonite at high-pressure: A contribution from first-principle simulations

Aragonite (CaCO3, space group Pmcn) is an important mineral for both geological and biological reasons, being one of the phases that recycles carbon in deep Earth conditions and the product of biomineralization of several terrestrial and marine organisms, respectively. Because of its ubiquity, aragonite has been the subject of several investigations to understand its elastic behaviour and stability at different P-T conditions, but the results reported in literature are still very scattered. Aiming at providing further details on this topic, in the present work we determined the structural and elastic properties of aragonite at absolute zero (0 K) within the Density Functional Theory framework, using a posteriori correction to include the weak long-range interactions. The equation of state parameters for this mineral phase, calculated between 0 GPa – 25 GPa, were K0 = 80.2(7) GPa, K’ = 4.37(10) and V0 = 223.00(6) Å3, in good agreement with the bulk modulus calculated from the elastic moduli (KR = 78.49 GPa). The results were compared to previous experimental and theoretical data, finding them in line with some specific studies, and show that some structural features (e.g., the carbonate ion aplanarity) could be related to the mechanism of phase transition to the post-aragonite phase at high pressure. The present work highlights the importance of including van der Waals interactions in the physical treatment of the structural and elastic properties of aragonite, and further extends the knowledge of the behaviour of this mineral as a function of pressure.

Phase transition by nanoindentation in a relaxor ferroelectric single crystal PMN-0.3PT: A phase-field investigation

Nanoindentaiton testing has revealed pop-in events in load–displacement curves of relaxor single crystal PMN-0.3PT ferroelectric materials that occur when the indentation depth is small (e.g., dozens of nanometers). Although there has been speculation of an occurrence of phase transition, there is a relative lack of investigation on the domain evolution associated with the phase transition when the pop-in events appear. In the present study, nanoindentation of this material was systematically modeled using phase-field simulations, which capture the domain and phase evolution of a PMN-0.3PT ferroelectric single crystal. The results, qualitatively similar to the experimental results, revealed details of the contribution of phase transformations to pop-in events. The influence of indenter shape, size, and external electric field on the pop-in event was also examined. This work provides a computational evaluation of the effects of the phase transition mechanism in ferroelectric materials under nanoindentation and gives insight into local mechanical loading effects on these electromechanically coupled crystals.

Multiple magnetic phase transitions and magnetocaloric effects of perovskite manganite

Perovskite La0.7Ca0.3Mn0.9Cu0.1O3 manganite was prepared and examined by X-ray diffraction. Multiple magnetic phase transitions and magnetocaloric effect were represented based on magnetic and specific heat measurements. The sample undergoes a first-order ferromagnetic - paramagnetic transition with a large thermal hysteresis, where the Arrott plots show negative slopes. A charge ordered phase occurs at TCO = 162 K, which can be melted under a sufficiently large magnetic field (µ0H ≥ 1 T) and thus result in a spin reorientation. The step-like jump of magnetization at Tb = 42 K in warming curves is caused by a blocked state, which is overcome by applying a magnetic field and leads to a metamagnetic transition. The successive multiple magnetic phase transitions broaden the operating temperature span and contribute to a large refrigerant capacity, in spite of mediocre magnetic entropy change and adiabatic temperature change. The adiabatic temperature change and phase transition mechanism were also discussed based on the recorded specific heat data.

Sub-Nanometer Electron Beam Phase Patterning in 2D Materials.

Phase patterning in polymorphic two‐dimensional (2D) materials offers diverse properties that extend beyond what their pristine structures can achieve. If precisely controllable, phase transitions can bring exciting new applications for nanometer‐scale devices and ultra‐large‐scale integrations. Here, the focused electron beam is capable of triggering the phase transition from the semiconducting T’’ phase to metallic T’ and T phases in 2D rhenium disulfide (ReS2) and rhenium diselenide (ReSe2) monolayers, rendering ultra‐precise phase patterning technique even in sub‐nanometer scale is found. Based on knock‐on effects and strain analysis, the phase transition mechanism on the created atomic vacancies and the introduced substantial in‐plane compressive strain in 2D layers are clarified. This in situ high‐resolution scanning transmission electron microscopy (STEM) and in situ electrical characterizations agree well with the density functional theory (DFT) calculation results for the atomic structures, electronic properties, and phase transition mechanisms. Grain boundary engineering and electrical contact engineering in 2D are thus developed based on this patterning technique. The patterning method exhibits great potential in ultra‐precise electron beam lithography as a scalable top‐down manufacturing method for future atomic‐scale devices.

Photoinduced Phase Transition of Ce-UiO-66 to Ce-BDC-OH.

External stimuli-responsive phase transition of metal-organic frameworks (MOFs) introduces intriguing functions for diverse applications under practical settings. Herein, we reported a phase transition from cubic Ce-UiO-66 to triclinic Ce-BDC-OH under light irradiation. Such a phase transition underwent a ligand-to-metal charge transfer process, which was unambiguously revealed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, electron paramagnetic resonance, etc. We proposed a phase transition mechanism through (1) the photoreduction of the metal core from Ce4+ into Ce3+; (2) the photogeneration of •OH and hydroxylation of BDC into BDC-OH; and (3) the carboxylate migration and lattice rearrangement for transitions. The phenomenon of the Ce4+-to-Ce3+ reduction also enables a diamagnetism-to-paramagnetism transition, suggesting its potential as a photostimulus-responsive magnetic switch.

Atomic-scale understanding of the reversible HCP↔FCC phase transition mechanisms at [formula omitted] twin tip in pure titanium

In this paper, by using high-resolution transmission electron microscopy (HRTEM) observations and molecular dynamics (MD) simulations, the mechanisms of hexagonal close-packed (HCP) structure to face-centered cubic (FCC) structure transition and its inverse transition at the {101¯1} twin tip in pure titanium were investigated. The HCP→FCC phase transition at the {101¯1} twin tip in cold-rolled pure Ti was experimentally observed for the first time. On the other hand, under electron beam irradiation, the FCC lamella shrank gradually and eventually recovered to the HCP structure. After the HCP↔FCC phase transformations, the interfacial structures of the twin tip changed from the (101¯0)T//(101¯3)M facets to a common Basal-Pyramidal (BPy) facets. MD simulations indicated that the reversible HCP↔FCC phase transitions were caused by successive slip of Shockley partial dislocations on {0001}HCPand{111}FCC planes, respectively. The nucleation of Shockley partial dislocations stemmed from the dissociation of twinning dislocation (TD) with the Burgers vector of b⇀4 = 4γ2−93+4γ2<101¯2¯> at the twin tip. The Shockley partial dislocations could be absorbed by twin tip boundaries through reacting with the residual dislocations to form new TDs b⇀4 during the FCC→HCP phase transition. The periodic serrated feature of the (101¯0)T//(101¯3)M facets of the twin tip boundaries in pure Ti was discovered via atomistic simulations. The interfacial structure evolution of the twin tip was caused by a series of dislocation reactions and generation of phase transformation at the twin tip. The transformation from the HCP structure to the FCC structures was due to the stress concentration caused by the plugging of the periodically distributed TDs b⇀4 at the twin tips in the case of external loading. The shrinkage of FCC lamella was caused by the relaxation of internal stress at the twin tip during the thermal relaxation by electron beam.

Electric-induced devil’s staircase in perovskite antiferroelectric

Antiferroelectric ceramics can realize ultra-high energy storage, which benefits from transformation between an antiferroelectric phase and a ferroelectric phase. Understanding the mechanism of such phase transition is the key point for building the structure-property correlation. Here, we report the observation of electric-induced devil’s staircase in the course of antiferroelectric–ferroelectric phase transition in PbZrO3-based antiferroelectric ceramics by in situ transmission electron microscopy. The dynamic evolution as-revealed in both reciprocal- and real-space involves stepwise rather than monotonic increase in modulation periods along with simultaneous proliferation of nanodomains. Desynchrony of phase transition is observed for incommensurate domains with different initial modulation periods within a single antiferroelectric domain. Then, the synergistic effect of the devil's staircase and as small as possible the initial modulation period is believed to contribute to the superior energy-storage performance. These findings will be helpful for the development of theories for antiferroelectric–ferroelectric phase transition and the design of high-power antiferroelectric materials.

The Semicoherent Interface and Vacancy Engineering for Constructing Ni(Co)Se2@Co(Ni)Se2 Heterojunction as Ultrahigh‐Rate Battery‐Type Supercapacitor Cathode

AbstractRestricted rate capability is the key bottleneck for the large‐scale energy storage of battery‐type supercapacitor cathode due to its sluggish reaction kinetics. Herein, Ni(Co)Se2@Co(Ni)Se2 semicoherent heterojunctions with rich Se vacancies (Vr‐Ni(Co)Se2@Co(Ni)Se2) as cathode are first constructed. Such a vacancy and heterointerface manipulation can not only essentially regulate the electronic structure and enhance ions adsorption capability, but also rationalize the chemical affinities of OH– ions in diffusion pathway revealed by systematic characterization analysis and first‐principle calculations. The as‐prepared cathode delivers large specific capacity of 264.5 mAh g–1 at 1 A g–1 and excellent cycle stability. Surprisingly, it presents ultrahigh rate with the retention of 159.7 mAh g–1 even at 250 A g–1. Moreover, the single phase transition mechanism of the cathode is elucidated systematically using series of ex situ techniques. In addition, contributed by the unique cathode and the self‐synthesized N/S co‐doped corncob‐derived porous carbon (N/S‐BPC, 316.1 F g–1 at 1 A g–1) anode, a high‐performance hybrid supercapacitor (HSC) is developed, which shows the energy density of 68.1 Wh kg–1 at 0.75 kW kg–1 and a superior cycle performance. The findings highlight a coordination strategy for the rational design of ultrahigh‐rate battery‐type HSC cathode, greatly pushing their commercial application processes.

Heat-induced solid-state polymorphic transition of 4,4′,5,5′- tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine (DATNBI)

Polymorphs of energetic materials generally exhibit distinct features, such as density, thermal stability, sensitivity, and detonation performance. These features are important in determining the appropriate applications of a given polymorph. To understand the thermal stability of new high explosive 4,4′,5,5′-tetranitro-1H,1′H- [2,2′-biimidazole]-1,1′-diamine (DATNBI), we systematically investigated its polymorphic transition (PT) under thermal stimulation and discovered a novel stable γ form of DATNBI. The results showed that the solid-solid PT path was β→α→γ. In this study, the three polymorphs of DATNBI were prepared through solvent recrystallization, and their PT processes in solution were explored. Crystal structure analysis of γ-DATNBI suggested that its special cross-cross grid crystal packing may be the main reason for its stable existence at room temperature and its lack of PT process before chemical decomposition, which starts at 240 ​°C. To further explore the PT process of DATNBI, the solid phase transition mechanism of DATNBI was analyzed using non-isothermal kinetics. The results demonstrated that the two high-temperature PT processes—β→α and α→γ—were not single-step reactions but complex multi-step reactions. The PT activation energy of the β→α process was slightly higher than that of the α→γ process. In addition, the influences of different polymorphs on the performance of DATNBI were explored. The results revealed that safety and detonation performance should decrease as a result of the incorporation of γ-DATNBI. This study contributes to understanding the PT behavior and the crystal structure evolutionary mechanism of DATNBI. This study provides practical support for formula design, process condition selection, and thermal stability evaluation of DATNBI explosives.

Phase transition and morphology evolution of superfine NaNbO3 particles synthesized by the hydrothermal method with the assistance of K+

NaNbO3 (NN) is a well-known perovskite-type dielectric material. However, its phase transition is a complex process and the phase transition mechanism is insufficiently investigated yet. Therefore, in the work, the NN superfine particles were synthesized by a hydrothermal method with the assistance of K+ and the microstructures of NN were carefully investigated to understand the strain-driven phase transition and morphology evolution of NN. The results suggest that K+ leads to strong planar bending of NbO6 by influencing the Na + vibration, which accounts for the O-R phase transition as the K+ increases. Once the R phase is triggered, the O-R phase transition proceeds spontaneously based on phonon calculations of orthorhombic (O) NN and R NN. The antiferroelectric nature of rhombohedral (R) NN with the space group R–3H is confirmed through charge density distribution. Additionally, the morphology evolution is deduced on the TEM analysis basis.

Phase transition properties of thin liquid films with various thickness on different wettability surfaces

Thin liquid film phase transition is often used to solve high heat flux heat transfer problem due to the high heat transfer coefficient. Both the surface wettability and the liquid film thickness are key factors affecting the phase transition behaviors of thin liquid films, however, the microscopic mechanism of the coupling effect is still unclear. Molecular dynamics method was employed to study the phase transition properties of liquid films with three thicknesses on six types of surfaces with different wettabilities, including hydrophilic, weak-hydrophilic, hydrophobic, and three hydrophilic-hydrophobic hybrid wettabilities. Results showed that explosive boiling occurred only when the temperature of the explosive boiling region reached the triggering temperature. The thermal resistance R1 at the solid-liquid interface, the thermal resistance R2 of the thin liquid film above the explosive boiling region, and their magnitude relationship determined the temperature rise rate of the explosive boiling region, then the phase transition mode and the onset time of explosive boiling (TOB) were further affected. Moreover, for hybrid surfaces, bubbles were easier to be generated in the hydrophobic region. The phase transition mechanism of thin liquid film on surface with different wettabilities was given in detail

Revealing Surface Restraint-Induced Hexagonal Pd Nanocrystals via In Situ Transmission Electron Microscopy.

Achieving metal nanocrystals with metastable phase draws much attention due to their anticipated fascinating properties, wheras it is still challenging because their polymorphism nature and phase transition mechanism remain elusive. Here, phase stability of face-centered cubic (fcc) Pd nanocrystals was studied via in situ spherical aberration (Cs)-corrected transmission electron microscopy (TEM). By constructing a well-defined Pd/C composite structure, Pd nanocrystals encapsulated by graphite, the dispersion process of fcc Pd was observed through a nucleation and growth process. Interestingly, Cs-corrected scanning TEM analysis demonstrated that the newly formed Pd nanocrystals could adopt a metastable hexagonal phase, which was considered challenging to obtain. Accordingly, formation mechanism of the hexagonal Pd nanocrystals was proposed, which involved the combined effect of two factors: (1) templating of graphite and (2) size effect. This work is expected to offer new insight into the polymorphism of Pd nanocrystals and pave the way for the future design of metastable metal nanomaterials.