Phase Evolution Process Research Articles

Potentiostatic strengthening tactic for constructing defects rich battery-type nickel-cobalt selenate for enhancing energy storage

Reasonably designing transition metal composite electrode materials with high defect levels can overcome the disadvantage of relatively moderate energy density in supercapacitors. Herein, an appealing potentiostatic strengthening tactic for constructing defect rich electrode materials is proposed. Notably, the densely nanoneedle-like nickel–cobalt-based selenide (NCSe) undergoes in situ electrochemical reconstruction after potentiostatic modification, with significant changes in morphology, structure, and composition. The highly active materials NCSe-E, transforming from weakly active substances NCSe mentioned above, are rich in oxygen vacancies and a large number of exposed active sites. Subsequently, it is compared with typical cyclic voltammetry (CV) scanning techniques and the phase evolution process is explored using in situ and ex situ methods. The results show that the plentiful defects promote the adsorption/desorption of OH–, leading to superior rate performance of NCSe-E, with a specific capacity of 3830 mC cm−2 at 1 mA cm−2 and capacity retention of 72.0 % at 50 mA cm−2. Kinetic analysis and theoretical calculations further reveal that oxygen vacancies enhance ions adsorption energy in NCSe-E and promote charge transfer during charging/discharging processes. This work indicates that the novel defect construction strategy provides some new insights for achieving reasonable regulation of high-performance transition metal compound electrode materials.

Deciphering the Morphology Evolution of Layer‐by‐Layer Processing Via In Situ Spectroscopy Measurement for High‐Performance Organic Photovoltaics

AbstractAlthough the layer‐by‐layer (LBL) processing can usually achieve an optimal bulk‐heterojunction morphology for high‐performance Organic photovoltaics (OPVs), the unambiguous working principles governing the morphology evolution are still lacking. To address this issue, here the phase‐separation kinetics of LBL processing are comprehensively studied using in situ spectroscopies, which are very sensitive to the intermolecular interactions, e.g. the molecular packing and D:A phase‐separation. Upon casting the nonfullerene acceptor (i.e., the BTP‐eC9) solution on top of the polymer donor, i.e., PM6, it is found that 1) the solvent will first swell the polymer and induce a polymer gel, 2) following the polymer gelation, the NFAs will immediately permeate into the cavities of polymer gel and form a molecular‐level D:A mixing, and 3) with the evaporation of the solvent, phase‐separation between the donor and acceptor occurs and results in a bulk‐heterojunction morphology as those achieved with blend‐cast processing. With these understandings, more diverse processing conditions have been purposely utilized to dictate the phase evolution process precisely. As a result, a high efficiency of 19.7% is reached, representing one of the best among binary OPVs. Therefore, this work deciphers phase‐separation kinetics of LBL processing and should pave the way toward advanced morphology control for high‐performance OPVs.

Simulation of lower Cambrian oil and gas generation and phase evolution process in ZH1 of Tazhong area

The Lower Cambrian petroleum system in the Tarim Basin has undergone multiple periods of tectonic movements, leading to successive hydrocarbon expulsion events and adjustments. The complex process of hydrocarbon accumulation occurred under deep burial conditions, persisting at depths of nearly 6,000 m over an extended period. This has resulted in the current occurrence of various phases including light oil, condensate, and gas in the deep-ultradeep strata of the Tarim Basin. The intricacies of formation of hydrocarbon accumulations and phase evolution have posed challenges to understanding the accumulation mechanisms and enrichment patterns of the Cambrian in the Tarim Basin, consequently lowering the success rate of oil and gas exploration. Such characteristics of multi-stage accumulation and adjustment are prevalent in deep hydrocarbon systems. Therefore, based on data from Well ZH1 in the Tazhong Uplift, combined with basin simulation, Compositional kinetics model, and PVT performance simulation, this study investigates the hydrocarbon generation and phase evolution processes in the deep hydrocarbon systems of the Tazhong Uplift. The results indicate that Well ZH1 entered the hydrocarbon generation peak during the Late Ordovician, followed by secondary cracking as the predominant hydrocarbon evolution process. Hydrocarbon fluids within the Lower Cambrian reservoir transitioned into the condensate phase towards the end of the Cambrian, with increasing depth resulting in higher gas-oil ratios and a decreasing trend in viscosity and density.

Surface Reconstruction of La2CuO4 during the Electrochemical Reduction of Carbon Dioxide to Ethylene and Its Benefits for Enhanced Performance.

Electrochemical reduction (ECR) of CO2 to C2H4 has a potential key role in realizing the carbon neutral future, which ultimately relies on the availability of an efficient electrocatalyst that can exhibit a high Faradaic efficiency (FE) for C2H4 production and robust, long-term operational stability. Here, for the first time, we report that upon applying reductive potential and electrolyte to the benchmark La2CuO4 catalyst, surface reconstruction occurred, i.e., the appearance of a distinctive phase evolution process over time, which was successfully monitored using ex situ powder XRD and operando Mott-Schottky (M-S) measurements of La2CuO4 samples that were soaked into the electrolyte and subjected to CO2-ECR for different durations. At the end of such a reconstruction process, an outermost layer consisting of lanthanum carbonate, a thin outer layer made of an amorphous Cu+ material formed over the core bulk La2CuO4, as confirmed by various characterization techniques, which resulted in the redistribution of interfacial electrons and subsequent formation of electron-rich and electron-deficient interfaces. This contributed to the enhancement in FE for C2H4, reaching as much as 58.7%. Such surface reconstruction-induced electronic structure tuning gives new explanations for the superior catalytic performance of La2CuO4 perovskite and also provides a new pathway to advance CO2-ECR technology.

Effect of Ca-Cu-O Particle Size on the Phase Evolution Process of Bi-2223 High-Temperature Superconductors

Effect of Ca-Cu-O Particle Size on the Phase Evolution Process of Bi-2223 High-Temperature Superconductors

Phase control of sulfide nanocrystals from thiourea-mediated solution

Nanomaterials that feature multiphase dictated by corresponding thermodynamic or kinetic conditions demonstrate great diversity for the exploration of novel properties like photovoltaics or thermoelectricity. To access a specific phase, especially those with a metastable nature, requires effective means to harness the determining parameters ruled by the intrinsic phase diagram. In this report, we develop a solvothermal model that is able to accurately tune the oxidation state of the metal ions in a sulfide system Cu-Sb-S, which in turn effectively regulates the phase evolution process to achieve the expected product (nanoparticles or film) in a phase pure form at a low temperature. The systematic in-situ and control investigations on different transient states illustrate the function of specific chemical groups in thiourea. Such an approach represents a general engineering method that can be readily employed in different systems, such as the Cu-Fe-S system. Furthermore, this one-pot synthetic strategy is capable of fine-tuning mix-phase sulfide nanocomposites as well. Therefore, it provides a platform to research sulfide’s phase-tunable properties, performance, and applications.

Intermediate Phase Suppression with Long Chain Diammonium Alkane for High Performance Wide-Bandgap and Tandem Perovskite Solar Cells.

Wide bandgap (WBG) perovskite can construct tandem cells with narrow bandgap solar cells by adjusting the band gap to overcome the Shockley-Queisser limitation of single junction perovskite solar cells (PSCs). However, WBG perovskites still suffer from severe nonradiative carrier recombination and large open-circuit voltage loss. Here, this work uses an in situ photoluminescence (PL) measurement to monitor the intermediate phase evolution and crystallization process via blade coating. This work reports a strategy to fabricate efficient and stable WBG perovskite solar cells through doping a long carbon chain molecule octane-1,8-diamine dihydroiodide (ODADI). It is found that ODADI doping not only suppresses intermediate phases but also promote the crystallization of perovskite and passivate defects in blade coated 1.67eV WBG FA0.7Cs0.25MA0.05Pb(I0.8Br0.2)3 perovskite films. As a result, the champion single junction inverted PSCs deliver the efficiencies of 22.06% and 19.63% for the active area of 0.07 and 1.02 cm2, respectively, which are the highest power conversion efficiencies (PCEs) in WBG PSCs by blade coating. The unencapsulated device demonstrates excellent stability in air, which maintains its initial efficiency at the maximum power points under constant AM 1.5G illumination in open air for nearly 500h. The resulting semitransparent WBG device delivers a high PCE of 20.06%, and the 4-terminal all-perovskite tandem device delivers a PCE of 28.35%.

Phase transitions, conductance fluctuations and distributions in disordered topological insulator stanene

It is essential to understand to what extent the protected edge states of topological insulators (TIs) can survive against the degradation of the ubiquitous disorders in realistic devices. From a different perspective, disorders can also help to enrich the applications by modulation of the phases in TIs. In this work, the phases and phase transitions in stanene, a two-dimensional TI, have been investigated via the statistical approach based on the random matrix theory. Using a tight binding model with Aderson disorder term and the Landauer–Büttiker formalism, we calculated the conductance of realistic stanene ribbons of tens of nanometers long with random disorders. The calculated phase diagram presents TI in the gap, metal in high energy and ordinary insulator in large disorder region. Increasing the width of the ribbon can significantly enhance the robustness of TI phase against disorders. Due to different underlying symmetries, the metallic phase can be further categorized into unitary and orthogonal classes according to the calculated universal conductance fluctuations. The local density of states is calculated, showing characteristic patterns, which can facilitate the experimental identification of the phases. It is found that different phases have distinguishing statistical distribution of conductance. Whereas at the phase boundary the distribution exhibits intermediate features to show where the phase transition occurs. To reveal the phase evolution process, we further studied the effects of the disorders on respective transmission channels. It is found that when phase transition takes place, the major transmission channels of the old phase are fading and the new channels of the new phase are emerging.

Alloying strategies for additive manufacturing of Ti6Al4V based alloys, composites and functionally graded materials: Microstructure and phase evolution of intra and inter-layer

The further developments of additive manufacturing (AM) provides a possibility for Ti6Al4V and its functionally graded materials (FGMs), but limits further applications due to its low ductility, low microhardness and poor wear resistance. The key lies in the presence of microstructures such as epitaxial columnar β-grain orientation and heterogeneous phase distribution in AM Ti6Al4V, as well as the interfacial bonding problems (intermetallic phases, delamination, cracking) in AM Ti6Al4V FGMs. In order to address these fundamental intra and inter-layer problems, firstly the microstructure and phase evolution process of AM Ti6Al4V columnar-to-equiaxed transformation (CET) promoted by some alloying strategies was summarized in this paper according to alloying elements and reinforcing particle types. Subsequently, controlled changes in the composition and microstructure of AM Ti6Al4V FGMs were achieved by adding interlayers/introducing gradient interfaces, and the metallurgical reactions and phase transformation mechanisms that inhibit the formation of intermetallic compounds and interfacial defects were explored. Finally, the difficulties and future research directions for alloying strategies to achieve high strength and ductility of AM Ti6Al4V were presented. This review aims to improve the reliability of AM Ti6Al4V and its FGMs for applications in critical load-bearing structures through in-situ alloying and multi-material for the microstructure design of AM Ti6Al4V.

The formation mechanism of in-situ TaC/Ni0.9Ta0.1 composites prepared by pressureless reactive sintering

The in-situ Tantalum Carbide (TaC)/Ni0.9Ta0.1 composite was fabricated by pressureless reactive sintering method using Nickel (Ni), Tantalum (Ta) and graphite as raw materials. The formation mechanism was investigated through analyzing the phase and morphology evolution process during the reactive sintering process. Results showed that Ni, Ta and graphite completely reacted and dense TaC/Ni0.9Ta0.1 composite was obtained. With the increase of temperature, the solid-phase diffusion of atoms occurs at the interface of Ni, Ta and graphite, leading to the formation of Ni3C, Ni2Ta, Ni3Ta, Ni0.9Ta0.1 and TaC. Meanwhile, the reaction [Ta] (Ta atoms in Ni3Ta) + [C] (C atoms in Ni3Ta)TaC in Ni3Ta takes place, due to the high affinity between Ta and C atoms. The intermediate products Ni3C, Ni2Ta and Ni3Ta vanish, and the composite is consisted of Ni0.9Ta0.1 and TaC before the appearance of liquid phase. The formation of TaC included two ways, namely the diffusion of C into Ta particles and the reaction [Ta]+[C] = TaC in Ni3Ta. Ni0.9Ta0.1 was also generated through two ways, i.e., the diffusion of Ta into Ni and the transformation of Ni3Ta. The liquid phase sintering of composite occurs at about 1320 °C, and the optimum sintering temperature was about 1380 °C.

Fabrication of Al2O3[sbnd]GAGG:Ce composite ceramic phosphors with excellent color quality for high-power laser-driven lighting

The application of high-power laser-driven lighting is limited by the insufficient heat dissipation of phosphor converters and the poor color quality of white light. In this study, the Al2O3(Gd,Ce)3(Al,Ga)5O12 (Al2O3GAGG:Ce) composite ceramics were designed to improve thermal performance of phosphors, while maintaining excellent color rendering under high-power laser excitation. Dense composite ceramics were fabricated by pre-sintering at 1600 °C in air followed by HIP at 1700 °C through the investigation of the phase evolution and sintering process. The emission spectrum of GAGG:Ce shows a red shift of 31 nm and a high full width at half maximum (FWHM) of 128 nm. Meanwhile, the thermal conductivity was increased to 13.2 W·m−1K−1 by addition of Al2O3, which is 72% higher than that of single-phase GAGG:Ce ceramic. Therefore, warm white light with high color rendering index (CRI) of 71.4 and low correlated color temperature (CCT) of 4352 K was attained under excitation of high-power LDs.

Formation, thermal stability, and infrared radiation properties of spinel-structured high-entropy oxides in Co–Mn–Fe–Cr–Ni–Zn–O system

Using a simple and scalable solid-state synthesis process, a series of spinel-structured high-entropy oxides were systematically designed and synthesized in a Co–Mn–Fe–Cr–Ni–Zn–O system. These included (Co,Mn,Fe,Cr)3O4, (Co,Mn,Fe,Ni)3O4, (Co,Mn,Fe,Cr,Ni)3O4, (Co,Mn,Fe,Zn)3O4, (Co,Mn,Fe,Cr,Zn)3O4, (Co,Mn,Fe,Ni,Zn)3O4 and (Co,Mn,Fe,Cr,Ni,Zn)3O4. The phase, microstructure and color evolution of 1/3Co3O4–1MnO-1/2Fe2O3-1/2Cr2O3–1NiO powders were studied without ZnO addition. These underwent four phase evolution processes and three color evolution processes before forming the final phase of black, octahedral (Co,Mn,Fe,Cr,Ni)3O4 powders. The formation of an intermediate phase of (Co,Mn,Fe)3O4 medium-entropy oxide powders served as the foundation for the creation of other high-entropy oxide powders. The infrared radiation properties of these synthesized medium and high-entropy oxides powders were evaluated in the near-infrared region at room temperature. Among these synthesized powders, the infrared emissivity values of (Co,Mn,Fe)3O4, (Co,Mn,Fe,Ni)3O4 and (Co,Mn,Fe,Cr,Ni)3O4 powders exceeded 0.8. All the synthesized powders exhibited excellent thermal stability after being annealed at high temperatures. Notably, after being annealed at high temperatures, the infrared emissivity values of these synthesized powders increased markedly without degradation, surpassing a value of 0.8, and displayed potential for applications in the field of high-temperature infrared energy savings.

Microstructural Characterization and Prior Particle Boundary (PPB) of PM Nickel-Based Superalloys by Spark Plasma Sintering (SPS).

This research investigates the microstructure and defects of powder metallurgy (PM) nickel-based superalloys prepared by spark plasma sintering (SPS). The densification, microstructural evolution, and precipitate phase evolution processes of FGH96 superalloy after powder heat treatment (PHT) and sintering via SPS are specifically analyzed. Experimental results demonstrate that SPS technology, when applied to sinter at the sub-solidus temperature of the γ' phase, effectively mitigates the formation of a prior particle boundary (PPB). Based on experimental and computational findings, it has been determined that the presence of elemental segregation and Al2O3 oxides on the surface of pre-alloyed powders leads to the preferential precipitation of MC-type carbides and Al2O3 and ZrO2 oxides in the sintering necks during the hot consolidation process, resulting in the formation of PPB. This study contributes to the understanding of microstructural modifications achieved through SPS technology, providing crucial information for optimizing sintering conditions and reducing the widespread occurrence of PPB, ultimately enhancing the material performance of PM nickel-based superalloys.

Reactive flash sintering of high-entropy oxide (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7: Microstructural evolution and aqueous durability

Herein, the phase evolution, densification and grain growth process of the high entropy ceramics during flash sintering were systematically characterized and quantified to understand the microstructural evolution for the first time. It was demonstrated that the densification rate of (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 by flash sintering in this work was generally around 60 times that of conventional sintering at 1600 °C, while the grain growth rate by flash sintering was only around 1.5–6 times that of conventional sintering, indicating that grain growth was suppressed during flash sintering. The grain growth mechanisms by flash sintering and conventional sintering could be both attributed to surface diffusion and volume diffusion. In addition, the flash sintered high-entropy ceramics as promising immobilization materials for high-level radioactive waste (HLW) exhibited excellent aqueous durability with normalized leaching rates of Nd, Gd and Zr approximately 10−6∼10−7 g m−2 d−1 after 42 days, which were much lower than most reported pyrochlore materials.

Operando Exploring and Modulating Phase Evolution Chemistry from MAX to MXenes in Molten Salt Synthesis.

Lewis acidic molten salt method is a promising synthesis strategy for achieving MXenes with controllable surface termination from numerous MAX materials. Understanding the phase evolution chemistry during etching and post-processing is highly desirable but remains a key challenge due to the lack of suitable in-situ characterizations and the complexity of the reaction process. Herein, we introduce an operando synchrotron radiation X-ray diffraction (SRXRD) technique to unveil the phase evolution process of Nb2GaC MAX under a molten-salt ambient, proposing a controllable synthesis to achieve optimal etching through precise temperature and time adjustment. Subsequently, the phase structure of Nb2CTx MXenes is successfully tailored from hexagonal to amorphous by time-dependent persulfate oxidation. The resulting amorphous Nb2CTx with a well-patterned morphology and numerous chloride terminations exhibits highly improved specific capacity, rate capability, and long cycling for Li+ storage with a Cl-containing surface protective film. Addressing the time-related phase evolution during the entire molten salt strategy provides new insights into achieving higher efficiency and controllability in preparing MXenes and shows great potential in high-performance energy storage systems based on MXenes.

Understanding the Synthesis Kinetics of Single-Crystal Co-free Ni-rich cathodes.

Non-equilibrium kinetic intermediates are usually preferentially generated, rather than thermodynamic stable phases in the solid-state synthesis of layered oxides. Understanding the inherent complexity between thermodynamics and kinetics is important for designing high cationic ordering cathodes. Single-crystal strategy is an effective way to solve the intrinsic chemo-mechanical problems of Ni-rich cathodes. However, the synthesis of high-performance single-crystal is very challenging. Herein, we explored a dynamically cationic ordering/disordering process in the synthesis of single-crystal Co-free Ni-rich (NM9505) to better understand the structural and morphological changes involved in the phase evolution process through non-equilibrium intermediates. We demonstrate that the kinetic reaction paths are regulated during the synthesis process to promote a low-temperature topotactic lithiation, which can reduce the defective intermediate structures and effectively inhibit the electrochemical-thermal-mechanical failure. This work provides a basis for designing high-performance single-crystal Co-free Ni-rich layered oxides by regulating the non-equilibrium intermediates to obtain the required structural/electrochemical properties.

Stabilized electrode phase by prelithiating V2O5 cathode materials for high-specific energy thermal batteries

Vanadium pentoxide (V2O5) is an attractive high-energy cathode material for thermal batteries but is limited by the high solubility and tendency to react with halogenic molten salt. LixV2O5 (0 < x ≤ 1) are expected to take the place of V2O5 as the promising cathode materials in thermal batteries. In this work, LixV2O5 were successfully synthesized by the high-efficiency and low-cost method, which uses the molten salt as lithium source and through a brief-time sintered process (900 °C for 15 s). LixV2O5/molten salt electrode with CNTs conductive agent exhibits an original discharge voltage with 2.51 V and a specific capacity up to 309.46 mA h g−1. The high chemical stabilization between LixV2O5 and molten salt which could increase interfacial structure stabilization and improve the transmission rate of Li+. Besides, CNTs could build the continuous electron transport channels in active cathode inter-particles and improve the utilization rate of LixV2O5. This paper not only prepares the LixV2O5 cathode materials with high specific capacity via a simple method, but also provides insights into the phase evolution process of V2O5 based cathode electrodes during discharge process of thermal batteries.

An Insight Into Wax Precipitation, Deposition, and Prevention Stratagem of Gas-Condensate Flow in Wellbore Region

Abstract Unlike conventional waxy crude oil, the condensate undergoes a complex phase evolution process in high-temperature and high-pressure conditions of a deep gas-condensate reservoir, which makes it more difficult to predict and prevent the wax precipitation. This study measured the component composition, physical properties, and carbon number distribution of the closed sampled condensates from the wellbore region. The fluid component in wells was corrected by combining with the gas–oil ratio of the actual production data. The wellbore temperature and pressure profiles were accurately predicted using the corrected component, and the phase envelope relationship of gas-condensate flow was reasonably determined. A cold finger apparatus was designed to test the wax deposition characteristics. The main test unit consists of a completely closed high-pressure autoclave and a cold finger with a maximum 140 °C temperature-tolerant and 16,000 psi pressure-tolerant ability. The wax deposition characteristics were formulated, including wax appearance temperature (WAT), critical conditions for wax deposition, wax crystal morphology, and wax deposition rate. The primary mechanisms causing wax deposition in the wellbore region of deep gas-condensate reservoirs are still thermal diffusion and molecular diffusion. A wax crystal improved wax inhibitor consisting of hydrocarbons and polymers was collected and employed. The wax crystal improved wax inhibitor showed remarkable wax prevention performance, reducing WAT by up to 80% and achieving a 90% wax inhibiting rate within the experimental measurement concentrations. These results offer insights into the wax precipitation behavior, wax deposition characteristics, and wax prevention of the condensates.

Thickness-dependent β/γ-NiOOH transformation of Ni-MOFs in oxygen evolution reaction

In-situ generated hydroxides and oxyhydroxides have been gradually recognized as the real active sites of metal organic frameworks (MOFs) towards the oxygen evolution reaction (OER). Nevertheless, the fine phase evolution process is still less of concern and elusive. Herein, we successfully construct serious of Ni-MOFs with differing thickness ranging from 1 nm to 270 nm through a competitive coordination strategy. Utilizing the operando resonance spectroscopy, an accurate phase inversion behavior of the Ni-MOFs has been witnessed during the OER, and demonstrated as a thickness-dependent process. Ultrathin architecture is identified as a positive factor to promote the exchange between MOFs ligands and applied electrolyte during the electrochemical test. Hence, after removing most of the internal ligands, 2D MOFs favor to be transformed as β-NiOOH, which is more active than the generated γ-NiOOH in bulky system. The density function theory (DFT) calculation alongside with the in-situ electrochemistry tests further affirm the β/γ-NiOOH transformation behavior. This work offers a new understanding of the electrocatalytic mechanism from the view point of phase evolution in 2D MOFs.

Intermetallic Reaction of the Bonding Interface of TA2/Q235 Explosive Welding Composite

During the explosive welding, the bonding interface of welded materials was fast heated due to high strain rate and drastic plastic deformation. The periodical wave interface, with an amplitude of ~300 μm and a period wavelength of ~800 μm, was identifiable as a uniform wave interface formed in the bonding interface. The details of the formation of melting zone and mixing zone of welding materials at the interface were observed. Combined with the Ti-Fe binary phase diagram and the principle of diffusion welding, the phase composition and evolution process of the melting and mixing zone of the bonding interface were investigated by transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). Significance of the intermetallic compound was found in the mixing zone and melting zone, which was mainly TiFe, TiFe2, TiO2, Fe2O3 and some other intermetallic oxides. Meanwhile, the phenomenon of the titanium agglomeration and oxygen precipitation was observed in the melting zone. The bonding interface could be determined as a mixing welding of mechanical mixing, melting, diffusion and solidification that occurred in the mixing zone, and melting welding and diffusion welding mainly occurred in the melting region.