Complete Phase Transition Research Articles

Assembling Smallest Prussian Blue Analogs Using Chiral Hydrogen Bond-Donating Unit toward Complete Phase Transition.

Exploring methods for assembling functional materials at the molecular level may yield functional expressions derived from the assembly method. This study developed novel switchable molecular assemblies characterized by abrupt, complete phase transitions promoted via hydrogen bonding with a chiral carboxylic acid. These assemblies were prepared by aggregating discrete molecules that are unresponsive to external stimuli. Furthermore, enantiopure hydrogen-bond donor (HBD) molecules provide switchable compounds with cooperative and abrupt phase transitions, whereas the racemic mixture of the HBD provides a hydrogen-bonded one-dimensional compound with a broad and incomplete phase transition when structural disordering is observed. This study presents a novel strategy for observing metal-to-metal electron-transfer-coupled spin transitions via hydrogen-bond formation.

Defect engineering and in-situ electrochemical oxidation promote lattice reconstruction of VO2 for boosting the energy storage of aqueous zinc-ion batteries

Finding a cathode with high capacity and rate performance is very important for the large-scale application of low-cost and safe aqueous zinc-ion batteries (AZIBs). In this work, VO2 containing oxygen rich vacancies (VO) was designed through fine regulation of the hydrothermal reaction, which was mainly due to the escape of crystalline water in the material. The rich oxygen vacancies in VO will adsorb water molecules in electrolyte and have redox reaction with water molecules, thus promoting the in-situ lattice reconstruction process. On the first charge of in-situ electrochemical oxidation process, VO undergoes a complete phase transition to an oxygen-deficient V2O5/V2O5·nH2O (O-VO), allowing subsequent (de)intercalation of zinc cations on the basis of the latter structure. The electrode thus has significant rate performance (376 mAh/g at 20 A/g). The energy density/power density at 20 A/g is 274 Wh kg−1/14550 W kg−1. This work provides fundamental insights into the formation of oxygen vacancies in materials, and for the first time combines defect engineering with in-situ electrochemical oxidation strategies, providing an innovative design strategy for constructing cathodes with high-rate capacity and high energy storage.

Observation of the liquid metal phase transition in optofluidic microcavities

Gallium (Ga) exhibits remarkable potential in flexible electronics, chemistry, and biomedicine due to its exceptional physical properties. The phase transition and supercooling characteristics of Ga have led to the emergence of numerous valuable applications. In this paper, we capitalize on this foundation by utilizing optofluidic microcavities supporting both high quality factor optical and optomechanical modes to investigate the phase transformation process and supercooling properties of Ga. Our study provides comprehensive insights into the dynamic behavior of Ga during the complete phase transition, such as measuring a hysteresis loop between the solid-to-liquid and liquid-to-solid transitions, revealing nonreciprocal resonance wavelength shift, and identifying a unique metastability state of Ga during melting. The linear thermal expansion coefficients of Ga were precisely measured to be 0.41 × 10−5 K−1 and −0.75 × 10−5 K−1 for solid and liquid Ga, respectively. Our research provides a comprehensive and versatile monitoring platform for newly fabricated liquid metal alloys, offering multidimensional insights into their phase transition behavior.

Numerical simulation of solidification of molten slag impacting inclined wall in boiler based on smoothed particle hydrodynamics method

In order to study the process of high temperature liquid slag impinging on the wall, the slagging phase change is produced by combustion of high alkali coal in a boiler chamber. In this paper, based on the smoothed particle hydrodynamics (SPH) method, the flow spreading and solidification model of slag particles hitting the inclined wall are established, and the dynamic process of flow spreading and the phase change of slag particles hitting the wall are analyzed by simulating the deposition process of the phase change of slag particles hitting the wall. The effects of different inclination angles of the wall on its deformation and solidification heat transfer are further discussed. It is shown that the change of inclination angle during the impact of single slag on the wall has a greater influence on the spreading flow process. During the impact of single/double slag on the wall with different inclination angles, the time taken by the double slag to reach the final spreading length and complete phase transition is nearly five times longer than that of the single slag. The direction of slag impact also has an effect on the spreading and phase transition. This SPH method provides a novel numerical simulation idea to study the kinetic behavior of molten slag hitting the wall and the problems related to phase change deposition in boilers.

Structural and Magnetic Transformations from CuCl to Cu2Cl(OH)3 Induced by H2O and CuCl2

This study explores the oxidation dynamics of “pure” CuCl during prolonged environmental exposure through X-ray diffraction and temperature-dependent magnetization assessments. While CuCl is traditionally considered diamagnetic, our investigation reveals the emergence of an antiferromagnetic transition at 4.7 K. This anomaly is potentially induced by the integration of water molecules into the CuCl matrix. The hydration process initiates a series of oxidation reactions, ultimately transmuting CuCl into Cu2Cl(OH)3. Over time, the distinctive diffraction pattern peaks corresponding to CuCl diminish, concurrently with the appearance and intensification of those ascribed to Cu2Cl(OH)3, culminating in a complete phase transition as confirmed by X-ray analysis. Correspondingly, magnetization measurements clearly discern magnetic transitions at 6.4 and 16 K, intensifying with the sample’s exposure duration. These findings illuminate the stark potential for probing the magnetic intricacies of Cu2Cl(OH)3, a subject that remains a compelling and unresolved intrigue within the field.

Room Temperature Crystallized Phase-Pure α-FAPbI3 Perovskite with In-Situ Grain-Boundary Passivation.

Energy loss in perovskite grain boundaries (GBs) is a primary limitation toward high-efficiency perovskite solar cells (PSCs). Two critical strategies to address this issue are high-quality crystallization and passivation of GBs. However, the established methods are generally carried out discretely due to the complicated mechanisms of grain growth and defect formation. In this study, a combined method is proposed by introducing 3,4,5-Trifluoroaniline iodide (TFAI) into the perovskite precursor. The TFAI triggers the union of nano-sized colloids into microclusters and facilitates the complete phase transition of α-FAPbI3 at room temperature. The controlled chemical reactivity and strong steric hindrance effect enable the fixed location of TFAI and suppress defects at GBs. This combination of well-crystallized perovskite grains and effectively passivated GBs leads to an improvement in the open circuit voltage (Voc) of PSCs from 1.08V to 1.17V, which is one of the highest recorded Voc without interface modification. The TFAI-incorporated device achieved a champion PCE of 24.81%. The device maintained a steady power output near its maximum power output point, showing almost no decay over 280h testing without pre-processing.

An experimental method of determination and validation of latent thermal energy storage dynamic characteristic by effective enthalpy

The paper draws attention to the problems of evaluating stored heat capacity in a latent heat thermal energy storage (LHTES) that operates with unsteady inlet temperature conditions. These problems are studied for custom-built LHTES designed to be charged/discharged at varying heat transfer rates in a chilled water system. The LHTES incorporates a typical fin and tube heat exchanger and commercially available ATP 20 phase change material (PCM). For the designed storage construction, the ratio of heat transfer area to PCM volume is 354 m2/m3, and the ratio of PCM volume to the total volume (compactness factor) is 0.87. The LHTES thermal characteristics were investigated on a test stand using inlet temperature inputs changing linearly at 1, 2 or 3 K/h. During each test, a complete phase transition in the PCM was ensured. Based on LHTES inlet and outlet temperature profiles, enthalpy distributions versus outlet temperature were evaluated. The experiments proved that these distributions are not a material property as they depend on the geometric characteristics of the LHTES and charging/discharging rates. However, they can describe the thermal behaviour of the PCM filling the LHTES and include the influence of a non-uniform temperature distribution inside the LHTES on the PCM hysteresis and temperature range of the complete melting/solidification. These effects can be modelled by the proposed function of effective enthalpy. The effective enthalpy allows for relatively simple monitoring of phase transition progression in the LHTES based solely on the parameters measurable outside the storage.

Gram-Scale Synthesis of Black Phosphorus through Shock-Induced Phase Transformation.

This article presents the utilization of a cylindrical double-tube shock loading device in conjunction with amorphous red phosphorus as the precursor to investigate the complete phase transformation of red phosphorus into black phosphorus under the influence of shockwaves. Multiple experiments were conducted by varying the shock pressure and temperature parameters. The characterization of the recovered samples involved analysis of the phase composition and microstructure. The obtained experimental results demonstrate that within the cylindrical double-tube shock loading setup, a pressure of 9 GPa and a temperature of 800 K are optimal for achieving the complete phase transition of amorphous red phosphorus into orthorhombic black phosphorus. By precisely controlling these experimental conditions, a high-quality orthorhombic black phosphorus powder with excellent crystallinity was successfully prepared. This method offers several advantages, including simplicity, cost-effectiveness, and high yield. Consequently, this presents a promising pathway for the industrial-scale production of black phosphorus. The implementation of this approach not only reduces the cost involved in black phosphorus synthesis but also contributes to the broad range of applications for this material.

Transport properties and electronic phase transitions in two-dimensional tellurium at high pressure

Utilizing in situ Raman spectroscopy, resistivity, and Hall-effect measurements, we conducted an extensive investigation on the continuous electronic phase transitions and transport properties of two-dimensional (2D) tellurium (Te) under high pressure at room and low temperature (80–300 K). The distinguishable decrease in the A1 Raman mode's full width at half maximum in the trigonal phase (Te-I) indicated an electronic phase transition at 2.2 GPa. The following Hall-effect experiments located the Lifshitz transition and the semiconductor-semimetal transition at 0.9 and 1.9 GPa, respectively, and the semiconductor-semimetal transition was also confirmed by resistivity variation through temperature. The charge carrier types of the Te changed from hole to electron during the phase transition from Te-I to Te-II (triclinic phase) at low temperature, while the transport parameters remained almost unchanged during the phase transition from Te-II to Te-III (monoclinic phase). The results offered complete and thorough electronic phase transitions and transport characteristics of 2D Te, hence great advancing the potential application of Te in electronic devices.

Recovery of consistency in thermodynamics of regular black holes in Einstein's gravity coupled with nonlinear electrodynamics

As one of candidate theories in the construction of regular black holes, Einstein's gravity coupled with nonlinear electrodynamics has been a topic of great concerns. Owing to the coupling between Einstein's gravity and nonlinear electromagnetic fields, we need to reconsider the first law of thermodynamics, which will lead to a new thermodynamic phase space. In such a phase space, the equation of state accurately describes the complete phase transition process of regular black holes. The Maxwell equal area law strictly holds when the phase transition occurs, and the entropy obeys the Bekenstein-Hawking area formula, which is compatible with the situation in Einstein's gravity.

Stabilizing Crystal Framework of an Overlithiated Li1+xMn2O4 Cathode by Heterointerfacial Epitaxial Strain for High-Performance Microbatteries.

To meet the increasing demands of high-energy and high-power-density lithium-ion microbatteries, overlithiated Li1+xMn2O4 (0 ≤ x ≤ 1) is an attractive cathode candidate due to the high theoretical capacity of 296 mAh g-1 and the interconnected lithium-ion diffusion pathways. However, overlithiation triggers the irreversible cubic-tetragonal phase transition due to Jahn-Teller distortion, causing rapid capacity degradation. In contrast to conventional lithium-ion batteries, microbatteries offer the opportunity to develop specific thin-film-based modification strategies. Here, heterointerfacial lattice strain is proposed to stabilize the spinel crystal framework of an overlithiated Li1+xMn2O4 (LMO) cathode by epitaxial thin film growth on an underlying SrRuO3 (SRO) electronic conductor layer. It is demonstrated that the lattice misfit at the LMO/SRO heterointerface results in an in-plane epitaxial constraint in the full LMO film. This suppresses the lattice expansion during overlithiation that typically occurs in the in-plane direction. It is proposed by density functional theory modeling that the epitaxial constraint can accommodate the internal lattice stress originating from the cubic-tetragonal transition during overlithiation. As a result, a doubling of the capacity is achieved by reversibly intercalating a second lithium ion in a LiMn2O4 epitaxial cathode with a complete reversible phase transition. An impressive cycling stability can be obtained with reversible capacity retentions of above 90.3 and 77.4% for the 4 and 3 V range, respectively. This provides an effective strategy toward a stable overlithiated Li1+xMn2O4 epitaxial cathode for high-performance microbatteries.

Structure and cryogenic mechanical properties of severely deformed nonequiatomic alloys of Fe–Mn–Co–Cr system

The work is devoted to a study of the structure and mechanical properties of two nonequiatomic medium-entropy nanocrystalline alloys, in which in a coarse state additional mechanisms act during plastic deformation — twinning (TWIP) in the Fe40Mn40Co10Cr10 alloy and phase transformations (TRIP) in the Fe50Mn30Co10Cr10 alloy. The nanocrystalline state in these alloys is achieved by high-pressure torsion (HPT) at 300 K and 77 K after different numbers of revolutions n = 0.25 and 5. In the nanostructural state in the TWIP Fe40Mn40Co10Cr10 and the TRIP Fe50Mn30Co10Cr10 alloys, a basically complete phase transition from the fcc lattice to hcp is observed, the content of which does not depend very strongly on the HPT temperature and deformation. For both alloys in the nanostructured state, there is a significant decrease in differences in the phase composition and microhardness Hv by comparison with the coarse-grained state. A decrease in the HPT temperature and an increase in HPT deformation for all the cases studied lead to an increase in the value of Hv. The Fe40Mn40Co10Cr10 TWIP alloy remains ductile under active compression deformation at 300 and 77 K, while there is no macroscopic plasticity in the Fe50Mn30Co10Cr10 TRIP alloy under similar conditions. For the Fe40Mn40Co10Cr10 TWIP the thermally-activated character of plastic deformation is retained during the transition from the coarse-grained to the nanostructured state.

Phase transition guided V2O5/β-Bi2O3 Z-scheme heterojunctions for efficient photocatalytic Hg0 oxidation

The incorporation of vanadium during the synthesis process induced a spontaneous and complete thermal phase transition from α-Bi2O3 to β-Bi2O3. This phase transition facilitated the development of intrinsic electric field at the interface between V2O5 and β-Bi2O3, consequently establishing a novel carrier transfer pathway. As a result, the fabricated V2O5/β-Bi2O3 heterojunction exhibited an outstanding removal efficiency of over 98 % for gaseous mercury (Hg0) under UV light, and this efficiency of 95.0 % even after 35 h of testing. Introducing vanadium enhanced the light absorption capacity in the ultraviolet region and effectively separated photoinduced charge carriers. As revealed by density functional theory calculations, the photoinduced electron–hole transfer in the V2O5/β-Bi2O3 heterojunction followed the Z-scheme mechanism. This mechanism significantly contributed to the long-term stability of photocatalytic Hg0 removal, even when H2O and NO were present. This study presents a novel material composited by a thermal phase transition technique, aimed at the highly effective and green removal of Hg0 in the environment.

Alkali metals induced stacking phase transition of graphite

It is well known that alkali metals can intercalate into graphite to form graphite intercalation compounds but the structural change of graphite induced by alkali metals has been paid less attention. Herein, we report that alkali metals (Li, Na, K) induce the phase transition from ABC-stacking (or 3R phase) to AB-stacking (or 2H phase) of graphite. Specifically, for the graphite powder containing ∼45% 3R phase in a mixed phase, the temperature needed to ensure a complete stacking phase transition is 600 °C, 500 °C or 350 °C, for Li, Na or K, respectively, much lower than that needed in bare annealing (1800 °C) while without these alkali metals. Simulations based on density functional theory (DFT) suggest that the charge transfer from alkali metals to graphene distinctly lowers the energy barrier of transition, explaining the different phase transition temperatures for these alkali metals.

Kinetic Control of Solvate Intermediate Evolution for High-Performance Perovskite Solar Cells by the Facial Mask Incubation Technique

The growth of high-quality perovskite films is complicated by the fact of uncontrollable crystallization pathways from perovskite precursors. During solution processing, extensive undesired nonperovskite products including residual solvate intermediates are produced due to quick solvent evaporation, which will adversely affect the efficiency and stability of perovskite solar cells (PSCs). Herein, we developed a highly efficient phase-transition pathway using a polydimethylsiloxane (PDMS)-based facial mask (FM) incubation technique, which enables significant reduction of the perovskite crystallization rate and depression of perovskite aggregation behavior. A surprising finding reveals that this technique induces complete phase transition from solvate intermediates to the perovskite phase, thereby obtaining phase-pure perovskite film. Meanwhile, a high-quality perovskite film with a shiny smooth surface, decreased defect states, and alleviated lattice strain is achieved after utilizing the FM strategy. Consequently, the target-inverted PSCs deliver a respectable efficiency of ∼21% and superior stability in both shelf storage (over 3700 h with 90% of initial efficiency) and light soaking (over 1000 h with 80% of initial efficiency) conditions. Our work highlights the importance of eliminating residual solvate intermediates to construct high-quality perovskites with excellent phase purity for ongoing production of high-performance perovskite-based optoelectronic devices.

Spinel-Derived Formation and Amorphization of Bimetallic Oxyhydroxides for Efficient Electrocatalytic Biomass Oxidation

Replacing the oxygen evolution reaction (OER) with water-assisted oxidation of organic molecules represents a promising approach for achieving sustainable electrochemical biomass utilization. Among numerous OER catalysts, spinels have received substantial attention due to their manifold compositions and valence states, yet their application in biomass conversions remains rare. Herein, a series of spinels were investigated for the selective electrooxidation of furfural and 5-hydroxymethylfurfural, two model substrates for versatile value-added chemical products. Spinel sulfides universally exhibit superior catalytic performance compared to that of spinel oxides, and further investigations show that the replacement of oxygen with sulfur led to the complete phase transition of spinel sulfides into amorphous bimetallic oxyhydroxides during electrochemical activation, serving as the active species. Excellent values of conversion rate (100%), selectivity (100%), faradaic efficiency (>95%), and stability were achieved via sulfide-derived amorphous CuCo-oxyhydroxide. Furthermore, a volcano-like correlation was established between their BEOR and OER activities based on an OER-assisted organic oxidation mechanism.

Water-Induced Structural Evolution of LaTMSi Ternary Intermetallic Electrides

Ternary intermetallic electrides (LaTMSi) are a class of electride materials that show excellent catalytic performance in hydrogenation reactions due to their unique geometric and electronic structures. Compared with conventional electrides, such as C12A7: e–, LaTMSi show higher structural stability of bulk phase in air and water. However, their catalytic activities decrease gradually in reaction systems with H2O as the product. In the previous literatures, the deactivation behavior was attributed to the fact that H atoms enter into the LaTMSi lattice, occupy the electron sites, and lower the electron-donating ability. As a solution, the catalytic activities were supposed to be recovered by calcinating LaTMSi at high temperatures. Herein, under a H2O-containing atmosphere, TEM observations reveal that an amorphous shell with a thickness of ∼3 nm can form on the surface of the LaCu0.67Si1.33 phase even at room temperature. This amorphous layer is relatively stable at room temperature and can prevent the bulk phase from further structural evolution. However, the amorphous layer will undergo peeling off at a high temperature, thus resulting in a new catalytic active surface. Therefore, high-temperature calcination is an effective method to strip away the deactivated surface on LaTMSi which was caused by occasional exposures to H2O. However, for H2O-containing catalytic systems, frequently alternating reactions with H2O and calcination will lead to complete phase transition from LaTMSi to the corresponding oxides. Taking the LaCu0.67Si1.33 sample as an example, X-ray powder diffraction proves the formation of the CuO2 phase at 500 °C under a H2O atmosphere. Therefore, LaTMSi materials should not be applied as catalysts in H2O-containing systems. In addition, the facile H2O dissociation over the LaCu0.67Si1.33 phase is verified by using various experimental approaches (e.g., cyclic H218O pulse-TPD, high-temperature H218O pulse-TPSR, and IR) and theoretical calculations. Moreover, similar surface dissociation of H2O and phase transition are also observed over LaCoSi and LaNiSi ternary intermetallic electrides.

Study on the Performance of Flexible Memory Device Based on Antimony Film

Antimony films and devices based on polyether-ether-ketone (PEEK) flexible substrates were fabricated. After bending at different radii for 24 hours, the antimony film still achieved a complete phase transition after heating. When the bending cycle was more than 10000 times, the resistance difference between amorphous and crystalline states kept more than one order of magnitude. With the increase of bending times, grains tended to be refined, resulting in a wider band gap. The good ductility of antimony film made it have small resistance drift in tensile state. The reversible SET and RESET operations were realized in bending phase change memory device. Antimony films based on PEEK substrates had great potential applications in flexible phase change memories.

Laser-driven first-order spin reorientation and Verwey phase transitions in magnetite Fe3O4 beyond the range of thermodynamic equilibrium

Ultrafast photo-induced phase transitions occurring under the impact of femtosecond laser pulses provide versatile opportunities for switching solids between distinctly-different crystalline, electronic, and magnetic states and thus modify their functional properties in a significant way. In this paper, we report on the laser-induced spin reorientation and Verwey phase transitions in a single crystalline ferrimagnetic magnetite ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$. Using femtosecond optical and magneto-optical pump-probe techniques, we define the range of the initial sample temperatures and laser fluences when partial or complete photo-induced phase transitions occur from a monoclinic insulating to a cubic metallic state with concomitant switching of magnetic anisotropy from the uniaxial to the cubic one. We thus reveal a connection between these phase transitions when driven by femtosecond laser pulses. Using transient linear and quadratic magneto-optical effects, we examine magnetization dynamics launched the switching of the magnetic anisotropy axis. We unveil the presence of the domains undergoing the laser-induced phase transitions even below the established threshold fluence for the transitions, as well as when the material is initially in the cubic phase. This is the manifestation of the first order of these both laser-induced phase transitions beyond the range of thermodynamic equilibrium.

Covalent inorganic complexes enabled zinc blende to wurtzite phase changes in CdSe nanoplatelets.

Phase changes in colloidal semiconductor nanocrystals (NCs) are essential in material design and device applications. However, the transition pathways have yet to be sufficiently studied, and a better understanding of the underlying mechanisms is needed. In this work, a complete ligand-assisted phase transition from zinc blende (ZB) to wurtzite (WZ) is observed in CdSe nanoplatelets (NPLs). By monitoring with in situ absorption spectra along with electrospray ionization mass spectrometry (ESI-MS), we demonstrated that the transition process is a ligand-assisted covalent inorganic complex (CIC)-mediated phase transition pathway, which involves three steps, ligand exchange on ZB CdSe NPLs (Step 1), dissolution of NPLs to form CICs (Step 2), and conversion of CdSe-CIC assemblies to WZ CdSe NPLs (Step 3). In particular, CICs can be directly anisotropically grown to WZ CdSe NPL without other intermediates, following pseudo-first-order kinetics (kobs = 9.17 × 10-5 s-1). Furthermore, we demonstrated that CICs are also present and play an essential role in the phase transition of ZnS NPLs from WZ to ZB structure. This study proposes a new crystal transformation pathway and elucidates a general phase-transition mechanism, facilitating precise functional nanomaterial design.