Insights into Ti doping for stabilizing the Na_(2/3)Fe_(1/3)Mn_(2/3)O_(2)cathode in sodium ion battery

Iron-and manganese-based layered metal oxides,as cathodes for sodium ion batteries,have received widespread attention because of the low cost and high specific capacity.However,the Jahn-teller effect of Mn^(3+)ions and the resulted unstable structure usually lead to continuously capacity decay.Herein,Titanium(Ti)has been successfully doped into Na_(2/3)Fe_(2/3)Mn_(2/3)O_(2)to suppress the Jahn-Teller distortion and improve both cycling and rate performance of sodium ion batteries.In situ high-energy synchrotron X-ray diffraction study shows that Ti-doped compound(Na_(2/3)Fe_(1/3)Mn_(0.57)Ti_(0.1)O_(2))can maintain the single P2 phase without any phase transition during the whole charging/discharging process.Various electrochemical characterizations are also applied to explore the better kinetics of sodium ions transfer in the Na_(2/3)Fe_(1/3)Mn_(0.5)7 Ti_(0.1)O_(2).This work provides a comprehensive insight into the Ti-doping effects on the performance from both structural and electro kinetic perspectives.

Multiscale structures and phase transitions in metallic glasses：A scattering perspective

Amorphous materials are ubiquitous and widely used in human society, yet their structures are far from being fully understood. Metallic glasses, a new class of amorphous materials, have attracted a great deal of interests due to their exceptional properties. In recent years, our understanding of metallic glasses increases dramatically, thanks to the development of advanced instrumentation, such as in situ x-ray and neutron scattering. In this article, we provide a brief review of recent progress in study of the structure of metallic glasses. In particular, we will emphasize, from the scattering perspective, the multiscale structures of metallic glasses, i.e., short-to-medium range atomic packing, and phase transitions in the supercooled liquid region, e.g., crystallization and liquid-to-liquid phase transition. We will also discuss, based on the understanding of their structures and phase stability, the mechanical and magnetic properties of metallic glasses.

Towards extreme fast charging of 4.6 V LiCoO_(2) via mitigating high-voltage kinetic hindrance

High-voltage LiCoO_(2)(LCO) is an attractive cathode for ultra-high energy density lithium-ion batteries(LIBs) in the 3 C markets.However,the sluggish lithium-ion diffusion at high voltage significantly hampers its rate capability.Herein,combining experiments with density functional theory(DFT) calculations,we demonstrate that the kinetic limitations can be mitigated by a facial Mg^(2+)+Gd^(3+)co-doping method.The as-prepared LCO shows significantly enhanced Li-ion diffusion mobility at high voltage,making more homogenous Li-ion de/intercalation at a high-rate charge/discharge process.The homogeneity enables the structural stability of LCO at a high-rate current density,inhibiting stress accumulation and irreversible phase transition.When used in combination with a Li metal anode,the doped LCO shows an extreme fast charging(XFC) capability,with a superior high capacity of 193.1 mAh g^(-1)even at the current density of 20 C and high-rate capacity retention of 91.3% after 100 cycles at 5 C.This work provides a new insight to prepare XFC high-voltage LCO cathode materials.

Simultaneously healing cracks and strengthening additively manufactured Co_(34)Cr_(32)Ni_(27)Al_(4)Ti_(3) high-entropy alloy by utilizing Fe-based metallic glasses as a glue

Solidification cracking issues during additive manufacturing(AM)severely prevent the rapid development and broad application of this method.In this work,a representative Co_(34)Cr_(32)Ni_(27)Al_(4)Ti_(3) high-entropy al-loy(HEA)susceptible to crack formation was fabricated by selective laser melting(SLM).As expected,many macroscopic cracks appeared.The crack issues were successfully solved after introducing a certain amount of Fe-based metallic glass(MG)powder as a glue during SLM.The effect of MG addition on the formation and distribution of defects in the SLM-processed HEA was quantitatively investigated.With an increasing mass fraction of the MG,the dominant defects transformed from cracks to lack of fusion(LOF)defects and finally disappeared.Intriguingly,the MG preferred to be segregated to the boundaries of the molten pool.Moreover,the coarse columnar crystals gradually transformed into equiaxed crystals in the molten pool and fine-equiaxed crystals at the edge of the molten pool,inhibiting the initiation of cracks and providing extra grain boundary strengthening.Furthermore,multiple precipitates are formed at the boundaries of cellular structures,which contribute significantly to strengthening.Compared to the brit-tle SLM-processed Co_(34)Cr_(32)Ni_(27)Al_(4)Ti_(3) HEA,the SLM-processed HEA composite exhibited a high ultimate tensile strength greater than 1.4 Ga and enhanced elongation.This work demonstrates that adding Fe-based MG powders as glues into SLM-processed HEAs may be an attractive method to heal cracks and simultaneously enhance the mechanical properties of additively manufactured products.

Effects of heat treatment on microstructures and properties of a heterostructured alloy with dissimilar components fabricated by WAAM

Heat treatment significantly influences homogeneous material microstructures and mechanical properties,which can be improved by an optimal heat treatment process.However,heat treatment application to heterogeneous materials presents significant challenges due to compositional and microstructural heterogeneities.Herein,a laminated heterostructured alloy comprising alternating316L stainless steel(SS)and 18Ni300 maraging steel(MS)layers fabricated using wire and arc additive manufacturing was investigated.A solution treatment was applied at900℃for 0.5 h.Subsequently,the solution-treated and asfabricated(AF)samples were aged at 500℃for 4 h;these samples were denoted SA and AT,respectively.The AT phase compositions and orientations were similar to those of AF.The SA 316L SS layer resembled that of AF,but the SA 18Ni300 MS layers exhibited a reduced austenite phase fraction and refined grain size,attributable to solid-state transformation.In the AT sample,aging induced the formation of nanoscale acicularωphase and ellipsoidal Ni_(3)Ti,Fe_(2)Mo,and X precipitates in the 18Ni300 MS layers.Conversely,the SA precipitates contained acicular Fe Ni_(2)and ellipsoidalω,Ni_(3)Ti,and X precipitates,and their fractions were lower than those in AT precipitates.The18Ni300 MS layer microhardness in the heat-treated samples increased due to nanoprecipitation,but the 316L SS layer microhardness resembled that of AF.The AT and SA ultimate tensile strengths increased to(1360±50)and(1473±41)MPa,respectively,attributable to precipitation strengthening.The SA 316L SS layer exhibited a high stress-induced martensite fraction,enhancing the ductility of heated samples.

Insight into structural degradation of NCMs under extreme fast charging process

Lithium-ion batteries(LIBs)with extreme fast charging(XFC)capability are considered an effective way to alleviate range anxiety for electric vehicle(EV)buyers.Owing to the high ionic and electronic conductivity of LiNi_(x)Co_(y)Mn_zO_(2)(x+y+z=1,NCM)cathodes,the inevitable Li plating of graphite in NCM|graphite cell is usually identified as a key bottleneck for XFC LIBs.However,the capacity decay mechanism of cathode materials under XFC has not been fully investigated.In this work,three typical NCM cathode materials with different Ni fractions were chosen and their electrochemical performances under XFC associated with structural evolution were investigated.A faster capacity decay of NCMs under XFC conditions is observed,especially for Ni-rich NCMs.In-situ X-ray diffraction(XRD)reveals that the multiple caxis parameters appear at the high-voltage regions in Nirich NCMs,which is probably triggered by the larger obstruction of Li(de)intercalation.Particularly,NCMs with moderate Ni fraction also present a similar trend under XFC conditions.This phenomenon is more detrimental to the structural and morphological stability,resulting in a faster capacity decay than that under low current charging.This work provides new insight into the degradation mechanism of NCMs under XFC conditions,which can promote the development of NCM cathode materials with XFC capability.

High-entropy design boosts dielectric energy storage

Dielectric capacitors are vital for advanced electronic and electrical power systems due to their impressive power density and durability.However,a persistent challenge has been enhancing their energy densities while maintaining high efficiency.Recently in Science,a novel high-entropy design for relaxor ferroelectric materials has been proposed,promising significant improvements in both energy density and efficiency for multilayer dielectric ceramic capacitors.Given the crucial role of high-entropy design in energy storage materials and devices,this highlight focuses on interpreting the progress and significance of this innovative work.

Recent progress on MOF-derived carbon materials for energy storage

Metal-organic frameworks(MOFs)are of quite a significance in the field of inorganic-organic hybrid crystals.Especially,MOFs have attracted increasing attention in recent years due to their large specific surface area,desirable electrical conductivity,controllable porosity,tunable geometric structure,and excellent thermal/chemical stability.Some recent studies have shown that carbon materials prepared by MOFs as precursors can retain the privileged structure of MOFs,such as large specific surface area and porous structure and,in contrast,realize in situ doping with heteroatoms(eg,N,S,P,and B).Moreover,by selecting appropriate MOF precursors,the composition and morphology of the carbon products can be easily adjusted.These remarkable structural advantages enable the great potential of MOF-derived carbon as high-performance energy materials,which to date have been applied in the fields of energy storage and conversion systems.In this review,we summarize the latest advances in MOF-derived carbon materials for energy storage applications.We first introduce the compositions,structures,and synthesis methods of MOF-derived carbon materials,and then discuss their applications and potentials in energy storage systems,including rechargeable lithium/sodium-ion batteries,lithium-sulfur batteries,supercapacitors,and so forth,in detail.Finally,we put forward our own perspectives on the future development of MOF-derived carbon materials.

Phase transformation behavior of a dual-phase nanostructured Fe-Ni-B-Si-P-Nb metallic glass and its correlation with stress-impedance properties

A study of the phase transformation process of a Fe-Ni-B-Si-P-Nb metallic glass using a suite of advanced characterization tools is reported.Transmission electron microscopy(TEM)and small angle neutron scattering(SANS)experiments show that the as-spun metallic glass ribbon has a dual-phase structure with bcc nanoclusters of a size of 2-3 nm.In situ high-energy X-ray diffraction(XRD)reveals a three-stage crystallization process when heating the metallic glass into supercooled liquid states.The isothermal annealing experiment shows the nanoclusters grow instantly without incubation.The easy formation and phase stability of the nanoclusters are due to the low interfacial energy between the amorphous matrix and clusters,as real space analysis shows that the nanoclusters and the amorphous matrix share similar short-to-mediumrange orders.We further find that the dual-phase structure reduces local magneto-anisotropy and enhances effective magnetic permeability,resulting in an excellent stressimpedance effect without sacrificing coercivity.Our work sheds light on the structure-property engineering of soft magnetic metallic glasses and provides a foundation for developing novel magnetic functional materials with nanostructured dual-phases.

Au掺杂MnO2催化剂表面Hg^0与Cl吸附状态理论研究

采用基于第一性原理的Materials Studio(MS)软件中量子力学模块CASTEP,对催化氧化烟气脱汞过程中Hg^0与Cl在Au掺杂改性前后MnO_2(110)表面各个吸附位点的吸附状况进行了计算机模拟.结果表明:掺杂有利于改善Cl和Hg^0在MnO_2表面的吸附状态,Hg^0与Cl均优先吸附于催化剂表面的氧活性位点上;烟气中的Cl和Hg^0在MnO_2表面不会发生竞争吸附,且Cl会优先于Hg^0占据催化剂表面的含氧活性位点.

Stress-induced phase transformation and phase boundary sliding in Ti: An atomically resolved in-situ analysis

In-situ tensile experiments on pure Ti were performed in a transmission electron microscope at room temperature.The dynamic process of stress-induced hexagonal closed-packed(hcp)to face-centered cu-bic(fcc)structural transformation ahead of a crack tip was captured at the atomic level.Intriguingly,a sliding behavior of the ensuing(0001)hcp/(1¯11)_(fcc) phase boundary was observed to further accommodate the plastic deformation until crack initiation.The sliding was accomplished via the successive conserva-tive glide of extended dislocations along the(0001)hcp/(1¯11)_(fcc) phase boundary.A molecular dynamics simulation was carried out to corroborate the experiments and the results confirm the new dislocation-mediated sliding mechanism.

Medium-range order endows a bulk metallic glass with enhanced tensile ductility

Developing ductile bulk metallic glasses(BMGs)can benefit from an in-depth understanding of the structure-property relation during plastic deformation.However,endowing BMGs with tensile ductility in BMGs needs to reveal the response of critical structure units during deformation.Here,we report the experimental results of an in-situ synchrotron high-energy X-ray study of a Zr-based BMG under uniaxial tension after preprocessing by canning compression of the three-dimensional compressive stress state.It is revealed that the canning-compressed BMG(CC-BMG)sample has better tensile ductility and higher ultimate strength than the as-cast sample,which possesses heterogeneous and loosely packed local struc-tures on medium-range scales.The experimental results revealed two stages of plastic deformation in the CC-BMGs compared with one stage of plastic deformation in the as-cast BMG.Moreover,the shift in the first sharp diffraction peak along the tension direction for the canning-compressed sample is substan-tially more pronounced than that of the as-cast sample.Furthermore,the real-space analysis illustrates a competition mechanism between the 2-atom and 3-atom connection modes on medium-range order during the plastic deformation of the CC-BMG.Additionally,the ordering on the medium-range scale de-creases in the first plastic deformation stage but increases in the second plastic deformation stage.There-fore,a structural crossover phenomenon occurs in the CC-BMG during plastic deformation.Our results demonstrate a structure-property correlation for the CC-BMGs of heterogeneous medium-range ordered structures,which may be beneficial for endowing BMGs with ductility based on medium-range order engineering techniques.

Evolution of medium-range order and its correlation with magnetic nanodomains in Fe-Dy-B-Nb bulk metallic glasses

Fe-based metallic glasses are promising functional materials for advanced magnetism and sensor fields.Tailoring magnetic performance in amorphous materials requires a thorough knowledge of the correlation between structural disorder and magnetic order,which remains ambiguous.Two practical difficulties remain:the first is directly observing subtle magnetic structural changes on multiple scales,and the second is precisely regulating the various amorphous states.Here we propose a novel approach to tailor the amorphous structure through the liquid-liquid phase transition.In-situ synchrotron diffraction has unraveled a medium-range ordering process dominated by edge-sharing cluster connectivity during the liquid-liquid phase transition.Moreover,nanodomains with topological order have been found to exist in composition with liquid-liquid phase transition,manifesting as hexagonal patterns in small-angle neutron scattering profiles.The liquid-liquid phase transition can induce the nanodomains to be more locally ordered,generating stronger exchange interactions due to the reduced Fe–Fe bond length and the enhanced structural order,leading to the increment of saturation magnetization.Furthermore,the increased local heterogeneity at the medium-range scale enhances the magnetic anisotropy,promoting the permeability response under applied stress and leading to a better stress-impedance effect.These experimental results pave the way to tailor the magnetic structure and performance through the liquid-liquid phase transition.

Enhanced activity and durability of FeCoCrMoCBY nanoglass in acidic hydrogen evolution reaction

In the present work,a multi-element nanoglass(m-NG)of FeCoCrMoCBY is obtained first time by the laser ablation combined with inert gas condensation(laser-IGC)technique.Compared with the conventional rapid-quenched metallic glass(MG)with identical composition,the Fe-based m-NG demonstrates a superior performance as a self-supported electrocatalyst for hydrogen evolution reaction(HER)in acidic solution.The enhanced HER activity of m-NG is proposed to be closely related to its high en-ergy states,which is originated from the unique inhomogeneous nanostructures with a high density of low-coordinated atoms.Additionally,the Fe-based m-NG exhibits an outstanding comprehensive catalytic performance even beyond the commercial Pt/C catalyst in long-term test due to its self-optimization ability.This work not only opens the way to the preparation of m-NGs by the novel laser-IGC technique,but also makes a great contribution to developing low-cost,high-efficient,and super-durable HER electrocat-alysts in acidic environment.

Unusual gradient stress induced superior room-temperature plasticity in brittle ferromagnetic bulk metallic glass

Ferromagnetic bulk metallic glasses(FBMGs)possess excellent soft magnetic properties,good corrosion resistance,and high strength.Unfortunately,their commercial utility is limited by their brittleness.In this work,we report the enhancement in the room-temperature plasticity during the compression(25%)and bending flexibility of Fe_(74)Mo_(6)P_(13)C_(7) FBMG by using water quenching.The high-energy synchrotron X-ray measurements,high-resolution transmission electron microscopy,three-dimensional X-ray microtomog-raphy,and finite element simulation were performed to reveal the origin.It was found that the M-shape profile of residual stress improves the mechanical properties of FBMGs,particularly their plasticity.The reversal of the heat-transfer coefficient and cooling rate from the'vapor blanket'to'nucleate boiling'transition during water quenching processing is the main cause of the unusual profile of residual stress in glassy cylinders.Encouraged by the progress in developing flexible silicate glasses,this work highlights a processing method to improve plasticity and surmount technical barriers for the commercialization of FBMGs.

Correlating dynamic relaxation and viscoelasticity in metallic glasses

Relaxation dynamics,essential for the structural evolution of non-equilibrium systems like glassy materials,remain enigmatic.Here,we explore relaxation dynamics and viscoelastic properties in three types of metallic glasses with distinctβrelaxation behavior.In systems with significantβrelaxation,stress relaxation and creep experiments reveal a transition from two-step to one-step relaxation with rising temperature.However,such a phenomenon is absent in systems with weakerβrelaxation.We model the two-step relaxation process using a double Kohlrausch-Williams-Watts equation,and the obtained relaxation times elegantly adhere to the Arrhenius relationship.By combining fitted activation energies with theoretical analysis,we conclusively attribute these relaxation processes toβrelaxation andαrelaxation,respectively.Finally,we analyze the relaxation time spectra of two processes and establish a comprehensive picture linking dynamic relaxation with viscoelasticity.Our study provides new strategies for probing the complex relaxation behaviors of glasses from the perspective of viscoelasticity.

Microstructure and magnetic properties evolution of Al/CoCrFeNi nanocrystalline high-entropy alloy composite

A systematic microstructure-oriented magnetic property investigation for Al/CoCrFeNi nanocrystalline high-entropy alloys composite(nc-HEAC)is presented.In the initial state,the Al/CoCrFeNi nc-HEAC is composed of face-centered cubic(FCC)-Al,FCC-CoCrFeNi and hexagonal close-packed(HCP)-CoNi phases.High energy synchrotron radiation X-ray diffraction and high-resolution transmission electron microscopy were used to reveal the relationship between microstructure evolution and mag-netic mechanism of Al/CoCrFeNi nc-HEAC during heat treatment.At low-temperature annealing stage,the mag-netic properties are mainly contributed by the HCP-CoNi phase.With the increase of temperature,the diffusion-in-duced phase transition process including the transformation of AlCoCrFeNi HEA from FCC to BCC structure and the growth of B2 phase plays a dominant role in the magnetic properties.It was found that the magnetic properties can be effectively regulated through the control of the thermal diffusion process.The nano dual-phase thermal diffusion-induced phase transition behavior of nanocomposites pre-pared based on laser-IGC technology provides guidance for the diffusion process and microstructure evolution of two phases in composites.

In situ scattering study of multiscale structural evolution during liquid–liquid phase transition in Mg-based metallic glasses

The glass-forming ability of Mg-Cu-Gd alloys could be significantly promoted with the addition of Ag.A calorimetric anomaly could be observed in the supercooled liquid region of the Mg-Cu-Ag-Gd metallic glass,indicating the occurrence of a liquid-state phase transition driven by entropy.However,the underlying mechanism of the polyamorphous phase transition remains unsettled.In the paper,in situ scattering techniques were employed to reveal multiscale structure evidence in a Mg65Cu15Ag10Gd10metallic glass with an anomalous exothermic peak upon heating.Resistivity measurements indicate a reentrant behavior for the Mg-Cu-Ag-Gd metallic glass in the anomalous exothermic peak temperature region during heating.In situ synchrotron diffraction results revealed that the local atomic structure tends to be ordered and loosely packed first,followed by reentering into the initial state upon heating.Moreover,time-resolved small-angle synchrotron X-ray scattering(SAXS) results show an increase in nanoscale heterogeneity first followed by a reentrant supercooled liquid behavior.A core-shell structure model has been used to fit the SAXS profiles when polyamorphous phase transition occurs.In contrast,there is no structure anomaly for the reference Mg-Cu-Gd alloy system.The detailed multiscale structural evidence suggests the occurrence of a liquid-liquid phase transition followed by a reentrant behavior in the MgCu-Ag-Gd metallic glass.Our results deepen the understanding of the structural origin of the glass-forming ability and shed light on the possibility of tuning the physical and mechanical properties by heat-treatment in the supercooled liquid region of Mg-based metallic glasses.

Ultrahard BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy formed by nanoscale diffusion-induced phase transition

In the current work,the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy(nc-HEA)with ultrahigh hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite.First,a dual-phase Al/CoCrFeNi nanocrystalline high-entropy alloy composite(nc-HEAC)was prepared by a laser source inert gas condensation equipment(laser-IGC).The as-prepared nc-HEAC is composed of well-mixed FCC-Al and FCC-CoCrFeNi nanocrystals.Then,the heat treatment was used to trigger the interdiffusion between Al and CoCrFeNi nanocrystals and form an FCC-AlCoCrFeNi phase.With the increase of the annealing temperature,element diffusion intensifies,and the Al Co Cr Fe Ni phase undergoes a phase transition from FCC to BCC structure.Finally,the BCC-AlCoCrFe Ni bulk nc-HEA with high Al content(up to 50 at.%)was obtained for the first time.Excitingly,the nc-HEAC(Al-40%)sample exhibits an unprecedented ultra-high hardness of 1124 HV after annealing at 500℃ for 1 h.We present a systematic investigation of the relationship between the microstructure evolution and mechanical properties during annealing,and the corresponding micro-mechanisms in different annealing stages are revealed.The enhanced nanoscale thermal diffusion-induced phase transition process dominates the mechanical performance evolution of the nc-HEACs,which opens a new pathway for the design of high-performance nanocrystalline alloy materials.

In Situ Scattering Studies of Crystallization Kinetics in a Phase-Separated Zr-Cu-Fe-Al Bulk Metallic Glass

Thermal stability and the crystallization kinetics of a phase-separated Zr-Cu-Fe-Al bulk metallic glass were investigated using in situ high-energy synchrotron X-ray and neutron diffraction,as well as small-angle synchrotron X-ray scattering.It was revealed that this glass with excellent glass-forming ability possesses a two-step crystallization behavior.The crystalline products and their evolution sequence are more complicated than a homogeneous Zr-Cu-Al glass with average glass-forming ability.The experimental results indicate that a finely distributed nanometer-sized cubic Zr_(2)Cu phase forms first and then transforms to a tetragonal Zr_(2)Cu phase,while the matrix transforms to an orthorhombic Zr_(3)Fe phase.The strength of the Zr-Cu-Fe-Al composite containing cubic Zr_(2)Cu phase and glass matrix increases,and the plasticity also improves compared to the as-cast Zr-Cu-Fe-Al bulk metallic glass.Our results suggest that the formation of multiple and complex crystalline products would be the characteristics of the Zr-Cu-Fe-Al glass with better glass-forming ability.Our study may shed light on the synthesis of bulk-sized glass-nanocrystals composites of high strength and good plasticity.