Phase Transformations In Materials Research Articles

Precise regulation of layered-to-rock structure of spent Li-ion cathodes achieving ultrahigh lithium recovery rate

With the rapid development of electric vehicles and digital devices, the accumulated spent lithium-ion batteries (LIBs) cause severe anxiety about lithium resources and environmental safety. However, the low capture rate of Li+ and the high chemical consumption of the existing recovery methods lead to high Li loss, treatment costs and disposal fees. Herein, we propose a universal strategy of spent LIBs recovery via precise directional regulating structures (from layered to rock) to achieve ultrahigh lithium recovery rate with super-low chemical and energy consumption. Experimental characterization and theoretical calculations reveal the dissociation of structure, reorganization of Li–O bonds and phase transformation of the cathode materials in the limited-domain reduction process, realizing the complete recovery of Li+ without consuming acid leaching agent. This process realizes an extra-high Li separation index (19154) and extra-long cycle half-life (173 cycles) which are far superior to those of traditional methods (9–191 and 7 cycles). Besides, ecological and economic analysis shows that the consumptions of chemicals and energy are only 9 % and 9.7 % those of the existing literature, respectively, providing a bright pathway for industrializable lithium batteries recycling.

Unraveling the contribution of nucleation to the intercalation energy barrier for phase-transforming Li-ion battery materials

Phase-transforming intercalation compounds, such as LiFePO4 (LFP) and Li4Ti5O12 (LTO), are widely utilized in Li-ion batteries, particularly for applications requiring high power and operation at low temperatures. However, the impact of phase transformation kinetics on energy density losses under extreme conditions has been largely unexplored. Specifically, the role of nucleation, the initial stage of phase transformation, in contributing to battery performance losses has not been previously investigated. In this study, we not only quantified the significance of material-level factors, such as interfacial charge transfer, in the low-temperature and high-rate performance of LFP and LTO materials, but also provided the first estimates of the apparent activation energies of nucleation. Our findings revealed that nucleation, particularly in the case of LFP, contributes significantly to overpotential, highlighting its pivotal role among material-level factors. Furthermore, our analysis allowed us to differentiate between material-level and particle-level limitations for the LTO/LFP cell, emphasizing the paramount importance of controlling the porosity of secondary particles to ensure high tolerance towards high-rate/low-temperature discharge.

An integrated exploration from microstructure to mechanics in austenite to pearlite transformation of high carbon steel under high magnetic fields

The effects of a high magnetic field (12 T) on the microstructural evolution and mechanical properties of high carbon steel during isothermal pearlitic transformation at 720 °C were investigated. The application of a high magnetic field effectively promotes pearlitic transformation and leads to a reduction in the lamellar spacing and the geometrically necessary dislocation density (GND) as well as to a slight increase in the grain size of the pearlite, which leads to a decrease in hardness. This is because the magnetic field reduces the magnetic Gibbs energy of ferrite and cementite, resulting in an increase in the driving force of phase transformation, which shortens the pearlite maturation time and reduces the nucleation barriers of pearlite, thereby accelerating the growth rate of pearlite. In addition, the interfacial energy of ferrite/cementite was found to be increased by the magnetic field from the thermodynamic point of view, and the mechanism of action of the magnetic field -induced precipitation of cementite in the form of particles and short rods was elucidated. The present work will enhance the understanding of the mechanism of magnetic field-induced phase transformation in iron-based materials.

(Invited) Operando Nanoimaging of Phase Transformations in Energy Storage Materials

We applied operando Bragg Coherent Diffractive Imaging (BCDI) to study the discontinuous phase transformation in LixNi0.5Mn1.5O4 embedded in a fully operational battery. During Li-intercalation, we observed nucleation and growth of the Li-rich phase in a 500 nm particle embedded in the multicomponent positive electrode. The data captures the evolution from a curved coherent to planar semi-coherent interface, driven by dislocation dynamics. These dislocations travel with the interface and are expelled upon the completion of the phase transformation, resulting in a crystal devoid of defects. We hypothesize that these defects move via glissile motion without diffusion of host ions. Our data indicate the absence of significant kinetic limitations affecting the transformation kinetics, even under rapid discharge within 2 hours. This study underscores the capability of BCDI as a powerful tool for operando analysis of nanoscale phase transformations, offering guidance for the design and optimization of electrochemical materials.

Evidence of non-isentropic release from high residual temperatures in shocked metals measured with ultrafast x-ray diffraction

Shock experiments are widely used to understand the mechanical and electronic properties of matter under extreme conditions. However, after shock loading to a Hugoniot state, a clear description of the post-shock thermal state and its impacts on materials is still lacking. We used diffraction patterns from 100-fs x-ray pulses to investigate the temperature evolution of laser-shocked Al–Zr metal film composites at time delays ranging from 5 to 75 ns driven by a 120-ps short-pulse laser. We found significant heating of both Al and Zr after shock release, which can be attributed to heat generated by inelastic deformation. A conventional hydrodynamic model that employs (i) typical descriptions of Al and Zr mechanical strength and (ii) elevated strength responses (which might be attributed to an unknown strain rate dependence) did not fully account for the measured temperature increase, which suggests that other strength-related mechanisms (such as fine-scale void growth) could play an important role in thermal responses under shock wave loading/unloading cycles. Our results suggest that a significant portion of the total shock energy delivered by lasers becomes heat due to defect-facilitated plastic work, leaving less converted to kinetic energy. This heating effect may be common in laser-shocked experiments but has not been well acknowledged. High post-shock temperatures may induce phase transformation of materials during shock release. Another implication for the study is the preservability of magnetic records from planetary surfaces that have a shock history from frequent impact events.

Revealing the Impact of Dual Site Modification on the Phase Transformation and Ion Transport Mechanism of Ni-Rich Cathode Materials.

Ni-rich cathode materials have garnered significant attention attributable to the high reversible capacity and superior rate performance, particularly in the electric vehicle industry. However, the structural degradation experienced during cycling results in rapid capacity decay and deterioration of the rate performance, thereby impeding the widespread application of Ni-rich cathodes. Herein, a Mg/Ti co-doping strategy was developed to boost the structure stability and Li-ion transport kinetics of the Ni-rich cathode material LiNi0.90Co0.05Mn0.05O2 (NCM9055) under long cycle. It is demonstrated that the Mg2+ ions inserted into the lithium layer could serve as pillars, enhancing the stability of the delithiated layer structure. The introduction of robust Ti-O bonding mitigated the detrimental H2-H3 phase transition (∼4.2 V) during cycling. In addition, despite the fact that Mg/Ti co-doping slightly reduces Li+ diffusion coefficient in the modified cathode material (NCM9055-MT), it effectively stabilized the robustness of the layered structure and maintained the Li+ diffusion channel while charging and discharging, thereby improving the Li+ diffusion coefficient after a long cycle. Therefore, the Mg/Ti co-doped cathode materials exhibited an exceptional capacity retention rate of 99.9% (100 cycles, 1 C). Additionally, the Li+ diffusion coefficient of the co-doped NCM9055-MT (2.924 × 10-10 cm2 s-1) after 100 cycles was effectively enhanced compared with the case of undoped NCM9055 (4.806 × 10-11 cm2 s-1). This work demonstrates that the Mg/Ti co-doping approach effectively enhanced the stability of layered Ni-rich cathode materials.

Phase Transformations in Na-Rich Prussian White Cathode Materials with Different Morphology

Phase Transformations in Na-Rich Prussian White Cathode Materials with Different Morphology

A Comparison of Sigma Phase Formation in Solubilized Hyper Duplex Stainless Steel and Super Duplex Stainless Steel Filler Metals

This study focuses on the kinetic analysis of sigma phase formation in filler metal wires on Super Duplex Stainless Steel (SDSS) and Hyper Duplex Stainless Steel (HDSS). Precipitation data reveal that in the solubilized microstructure, sigma phase kinetics are more prominent in SDSS. This increased susceptibility is attributed to the greater number of nucleation sites, which is facilitated by the larger interface area/volume and the higher chromium content in the ferrite. The difference in interface area/volume is significantly more influential in determining kinetics than the composition difference, with nucleation sites playing a central role. The sigma phase transformation in both materials was modeled using the JMAK kinetic law. The JMAK plots exhibit a transition in kinetic mechanisms, evolving from discontinuous precipitation to diffusion-controlled growth. In SDSS, the JMAK values indicate “grain boundary nucleation after saturation,” followed by “thickening of large plates.” In contrast, HDSS values point to “grain edge nucleation after saturation,” followed by “thickening of large needles.” The higher kinetics in SDSS are characterized by a smaller nucleation activation energy of 56.4 kJ/mol, in contrast to HDSS's 490.0 kJ/mol. CALPHAD-based data support the JMAK results, aligning with the maximum kinetics temperature of SDSS (875 °C to 925 °C) and HDSS (900 °C to 925 °C). Therefore, the JMAK sigma phase kinetics effectively describe the experimental data and its dual kinetics behavior, even though CALPHAD-based TTT calculations often overestimate sigma formation.

Features of Phase Transformations in Porous Powder Materials

Features of Phase Transformations in Porous Powder Materials

Constructing partially spinel phase in Mn-rich cathode material

As a cathode with earth-abundant element, Mn-rich oxide has been explored to enable the scaling of the Li-ion battery. However, the irreversible transition metals migration and phase transformations in Mn-rich materials have been proven to be detrimental, which trigger capacity degradation, voltage decay, and poor kinetics. In this work, using Li2MnO3 as model, spinel-layered biphase was constructed via Ti doping and de-lithiation modification, which exhibits higher available capacity of 236.9 mAh/g (55.6 mAh/g for pristine material) and improved rate performance. Compared with pristine Mn-based cathodes, the new phase delivers neglectable voltage degradation during electrochemical cycling. Based on systematic characterization, the new phase exhibits higher oxygen redox reversibility and accelerated kinetics of lithium ions transformation. This work provides a new strategy for designing high-energy density Mn-rich cathodes.

Effect of milling atmosphere on stability and surface properties of ZnO/vermiculite hybrid nanocomposite powders

The zinc acetate dihydrate and anhydrous zinc chloride were used as precursors for the sonochemical preparation of the zinc oxide/vermiculite and organically modified zinc oxide/vermiculite_chlorhexidine nanocomposite materials. The nanocomposites were mechanically processed via a high-energy ball milling for 30 min at 300 rpm using two types of atmospheres an air or a nitrogen. Changes in temperature and pressure inside the grinding vessels were measured during mechanical processing in an air atmosphere. The ZnO(Cl)/V_30/300 sample reached the highest pressure (1161 mbar) and temperature (30.3 °C) in the milling vessels and for the ZnO(ac)/V_CH_30/300 sample the highest temperature difference was measured at the beginning and at the end of the milling (7 °C). The phase transformation, chemical composition and particle size of the hybrid nanocomposite materials were investigated using X-ray diffraction method, Fourier-transform infrared spectroscopy, X-ray fluorescence spectroscopy, carbon phase analysis and particle size distribution analysis. Changes in morphology and particle arrangement were characterised using scanning electron microscopy. The effect of mechanical processing in a protective atmosphere on surface properties such as specific surface area, surface conductivity and ζ-potential were demonstrated in relation to the type of precursor used for the preparation of ZnO nanoparticles in the structure of hybrid nanocomposite materials.

Nanocalorimeter and Raman microscope combination technique to study polymorphic transition processes in pharmacy materials

This article describes an experimental setup for combining ultrafast on-chip calorimetry (nanocalorimetry) and Raman spectroscopy (Raman spectroscopy) to study phase transformations in polymer materials. A new method for calibration of a nanocalorimetric sensor under a laser beam of a Raman microscope for in situ measurements at various temperatures is developed.

Investigate on material removal of 3C-SiC crystals in nano-polishing via molecular dynamics

While 3C-SiC crystals are widely employed in engineering applications such as aerospace, energy, chemistry, and electronics, the challenge of enhancing surface friction and wear mechanisms in 3C-SiC materials persists. This work focuses on the nano-polishing velocity effect on the material removal mechanism of 3C-SiC crystals in the course of nano-polishing, which is related to material removal, mechanical response, phase transformation, and stress distribution. By employing molecular dynamics (MD) simulations, nano-polishing velocity is modified within a specified range, and its influence on the atomic motion and structural transformation of the workpiece is examined. The simulation results reveal that higher nano-polishing velocities diminish the subsurface damage and the extent of phase transformation induced by nano-polishing. However, the higher velocities also result in reduced machined surface quality and increased residual stress in 3C-SiC crystals. Therefore, it is challenging to address both the surface quality and subsurface quality of the material solely based on nano-polishing velocity. A recommended range of nano-polishing velocity, ranging from 200 m/s to 400 m/s, is deemed appropriate. This work offers a comprehensive understanding of the material removal mechanism of 3C-SiC at the atomic level and holds significant guiding value for achieving ultra-precision machining of surfaces and subsurfaces.

Theoretical investigation on the solid-liquid phase transition of gallium through free energy analysis.

Gallium, renowned for its notably low melting point and unique property of becoming liquid at room temperature, is a valuable constituent in phase change materials. In this study, we investigate the solid-liquid phase transition of gallium using the modified embedded atom method (MEAM) potential. It addresses the technique to compute the free energy difference between the solid and liquid without using a reference state. We examine various thermodynamic and dynamic properties, including density, specific heat capacity, diffusivity, and radial distribution functions. We compute the coexistence temperature of the solid-liquid phase transitions of gallium from free energy analysis. This information is crucial for understanding the behavior of the material under different pressure conditions and can be valuable for various applications, such as materials processing and high-pressure studies. The analysis, findings, and insights of the present work will be of great significance to the broad scientific and engineering communities in the field of phase transformation of materials. A series of molecular dynamics(MD) simulations were conducted using the LAMMPS software packages. The gallium atoms are modeled using the modified embedded atom method (MEAM) potential. To accurately predict the solid-liquid phase transitions of gallium, we calculated free energy by employing the "constrained λ integration" method, coupled with multiple histogram reweighting (MHR). The solid-liquid coexistence line is determined through the Gibbs-Duhem integration technique.

In situ annealing optimization by anomalous Hall effect for a high-entropy alloy

An in situ methodology was devised to refine the annealing parameters for a soft magnetic high-entropy alloy, Al0.7NiCoFe1.5Cr1.5. Anomalous Hall measurements were employed to elucidate the magnetic characteristics in real time during annealing. This approach facilitates the determination of an optimal annealing temperature range, centered approximately at 500 °C, within a single annealing process. After annealing, a notable 51.5% enhancement in the saturation magnetization was observed, accompanied by a significant 80.5% reduction in coercivity. Moreover, the methodology enables the acquisition of intricate insights into phase transitions occurring throughout the annealing process. The findings affirm the efficacy of the in situ technique for refining the annealing parameters and underscore its potential applicability in the exploration of microstructural and phase transformations in materials.

Plasma and Gas‐based Semiconductor Technologies for 2D Materials with Computational Simulation & Electronic Applications

AbstractThe technique of plasma processing is beneficial for wafer cleaning and precision etching of integrated circuits and essential in manufacture of advanced semiconductor devices with unmatched perfection. Research on two‐dimensional (2D) materials, such as transition metal dichalcogenides(TMDs), offers a promising solution to the challenges in semiconductor miniaturization. TMDs, with their atomic layer thicknesses and silicon‐like bandgaps, can be integrated using existing plasma systems. Different 2D crystal structures, such as 1T and 2H configurations, exhibit distinctive properties. Computational approaches are also developed to provide guidelines for controlled synthesis and etching of large‐scale and high‐quality 2D materials. Plasma/gas‐surface interactions during the synthesis, etching, and phase transformation of 2D materials are explored using atomistic simulations such as density functional theory and molecular dynamics. The reaction energetics, chemical species, and associated kinetics are discovered in the simulation study. These results decipher various mechanisms of 2D materials processing at the microscopic scale and predict certain optimal process parameters. Plasma/gas‐based semiconductor technologies are crucial in electronics because they enable production of advanced semiconductors. Plasma/gas etching allows precise and selective removal of material and plasma‐enhanced chemical vapor deposition enhances chemical reactions for efficient film deposition; therefore, these processes are majorly important for harnessing 2D materials in electronic applications.

Preparation and Properties of Graphene/Novel Degradable Plastics Hybrid Low Enthalpy of Phase Transition Materials

Graphene (GNs) were chosen to modify hybrid and novel degradable plastics PTLA/polymethyl methacrylate (PMMA). The low enthalpy of melting phase transformation (MEPT) materials (PTLA/PMMA)/GNs were prepared by adding the GNs at different mass fraction(1%, 2%, 3%, 4%) into PTLA/PMMA, and the properties of the hybrid phase change materials were characterized. The results indicated that the MEPT of PTLA/PMMA materials can be significantly reduced with the addition of GNs. The addition of 3% (mass) GNs made the MEPT of PTLA/PMMA material decreased by more than 50%. With the increase of GNs mass fraction, the MEPT hardly changed; Fourier transformed infrared (FT-IR) spectra showed that the interaction between GNs and PTLA/PMMA was physical; Scanning electron microscope (SEM) images showed that the components of GNs and PTLA/PMMA were mixed evenly without phase separation; The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) cycle performance tests showed that the decomposition temperature of the (PTLA/PMMA)/GNs material was up to 280 °C, and the properties could remain stable during the circulation process. The addition of GNs could effectively reduce the MEPT of the (PTLA/PMMA)/GNs material, increase the heat transfer efficiency, and have good thermal reliability.

Особенности фазовых и структурных превращений в композиционных материалах на основе систем несмешивающихся компонентов при воздействии концентрированных потоков энергии

The features of phase and structural transformations in composite materials based on systems of immiscible components Al – Be, Al – Be – Mg, Fe – Cu, Fe – Cu – Pb under the influence of concentrated heat sources — electric arc, electron and laser beams — are considered. It is shown that when materials of the Al – Be, Al – Be – Mg systems are exposed to an electric arc plasma and an electron flow, they are melted and subsequently cooled by grain grinding, formation of a zone of thermal influence and crystallization of the resulting new structures and phases. In zone of thermal influence, the enrichment of the aluminum matrix with Be particles is observed due to the thermal diffusion processes of their movement. When plasma is exposed to an arc discharge, pulsed and continuous laser radiation, as well as the flow of electrons on the composition Fe – Cu, Fe – Cu – Pb, a change in the morphology of the near-surface layer is observed: the irradiated material in the melt zone is exfoliated and in the process of crystallization the stratified phases are fixed in a solid state. The mechanism of stratification formation is associated with the limited solubility of the elements that make up the composition in the liquid and solid states.

Grain size and lattice compatibility enhanced figure-of-merit in Ba0.95Ca0.05Ce0.005ZrxTi0.995−xO3 material for pyroelectric energy conversion

Phase-transforming ferroelectric materials have attracted significant attention due to their potential for energy conversion from waste heat. Here, we explore the impact of grain size and lattice compatibility on the energy conversion figure-of-merit (FOM) of a phase-transforming ferroelectric system Ba0.95Ca0.05Ce0.005ZrxTi0.995−xO3 with Zr content ranging from 0.004 to 0.03. The results demonstrate that tuning grain size and lattice compatibility can significantly increase the FOM. The optimal composition Zr0.006 exhibits the highest FOM among its neighboring compositions, with a corresponding peak pyroelectric current density of 5.6 μA/cm2 generated from a temperature fluctuation of 30 °C at a temperature rate of 5 °C/s. This work provides a rational understanding of the effect of grain morphology and crystal structure on the pyroelectric properties for energy conversion.

(Invited) Some Perspectives on Thermodynamics, Kinetics, Mechanics and Phase Transformations of Ionic and Mixed Conducting Ceramics

A perhaps oversimplified description of Professor Virkar's research of the last 45 years is thermodynamics, kinetics, (fracture) mechanics--which is thermodynamics at 0 Kelvin, and phase transformations of ceramic materials. I will reflect on some of his significant contributions in these areas, and echo them with a few recent research notes of my own.