Accelerated intermetallic phase amorphization in a Mg-based high-entropy alloy powder

We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expedites the synthesis of amorphous alloy powder by strategically injecting entropic disorder through the inclusion of multi-principal elements in the alloy composition.Predictions from first principles and materials theory corroborate the results from microscopic characterizations that reveal a transition of the amorphous phase from a precursor intermetallic structure.This transformation,characterized by the emergence of antisite disorder,lattice expansion,and the presence of nanograin boundaries,signifies a departure from the precursor intermetallic structure.Additionally,this phase transformation is accelerated by the presence of multiple principal elements that induce severe lattice distortion and a higher configurational entropy.The atomic size mismatch of the dissimilar elements present in the alloy produces a stable amorphous phase that resists reverting to an ordered lattice even on annealing.

Promoting amorphization of commercial TiO_(2) upon sodiation to boost the sodium storage performance

Anatase TiO_(2) is a promising anode material for sodium-ion batteries,yet the low electronic and ionic conductivities are the main obstacles for its practical application.Even though the amorphization of TiO_(2) upon sodiation has already been observed,its underneath mechanisms are not fully elucidated.Herein,a low-cost nitrogen-containing carbon source of polyacrylonitrile is adopted to modify commercial anatase TiO_(2) by a convenient and nontoxic ball-milling technique combined with subsequent annealing treatment.In particular,the employment of a nitrogen-doping approach accompanied by nitrogendoped carbon coating,results in a greatly improved conductivity,overall leading to a high reversible capacity of about 260 m A h g^(-1)at 25 m A g^(-1),superior rate capabilities,and an ultra-stable capacity of about 186 m A h g^(-1)after 1600 cycles at 500 m A g^(-1).Detailed characterizations denote that the improved conductivity as well as the small size of the synthesized TiO_(2) grains play a key role in the TiO_(2) amorphization upon sodiation,with the TiO_(2)/C nanocomposite undergoing a complete amorphization in just few cycles.Finally,the irreversible amorphization of TiO_(2) is confirmed to be a crucial ingredient facilitating the Na+diffusion kinetics and pseudocapacitive behavior,thus boosting the sodium storage performance.

Effects of Cr_3C_2 content and wheel speed on amorphization behavior of melt-spun SmCo_(7-x)(Cr_3C_2)_x alloys

The effects of the Cr3C2 content and wheel speed on the amorphization behavior of the melt-spun SmCo7-x（Cr3C2）x （x=0.10-0.25） alloys were studied systematically by X-ray diffraction analysis （XRD）, differential scanning calorimetry （DSC） and magnetic measurements. The ribbon melt-spun at lower wheel speed （20 m/s） has composite structure composed of mostly SmCo7 and a small amount of Sm2Co17R. The grain size of SmCo7 phase decreases with the increase of Cr3C2 content. With the increase of wheel speed, the XRD peaks become lower and accompanied with a broad increase in backgrounds, indicating a considerable decrease in the grain size of the SmCo7 phase. When the wheel speed increases to 40 m/s, SmCo7-x（Cr3C2）x alloys can be obtained in the amorphous state for 0.15≤x≤0.25 with intrinsic coercive Hci of 0.004-0.007 T. The DSC analysis reveals that SmCo7 phase firstly precipitates from the amorphous matrix at 650 °C, followed by the crystallization of Sm2Co17 phase at 770 °C.

Amorphization activated FeB_(2) porous nanosheets enable efficient electrocatalytic N_(2) fixation

Designing active,robust and cost-effective catalysts for the nitrogen reduction reaction(NRR) is of paramount significance for sustainable electrochemical NH3 synthesis.Transition-metal diborides(TMB_2)have been recently theoretically predicted to be a new class of potential NRR catalysts,but direct experimental evidence is still lacking.Herein,we present the first experimental demonstration that amorphous FeB_2 porous nanosheets(a-FeB_2 PNSs) could be a highly efficient NRR catalyst,which exhibited an NH3 yield of 39.8 μg h^(-1) mg^(-1)(-0.3 V) and a Faradaic efficiency of 16.7%(-0.2 V),significantly outperforming their crystalline counterpart and most of existing NRR catalysts.First-principle calculations unveiled that the amorphization could induce the upraised d-band center of a-FeB_2 to boost d-2π~* coupling between the active Fe site and ~*N_2 H intermediate,resulting in enhanced ~*N_2 H stabilization and reduced reaction barrier.Out study may facilitate the development and understanding of earth-abundant TMB_2-based catalysts for electrocatalytic N_2 fixation.

Krypton ion irradiation-induced amorphization and nano-crystal formation in pyrochlore Lu_2Ti_2O_7 at room temperature

Polycrystalline pyrochlore Lu2Ti2O7 pellets are irradiated with 600-keV Kr^3＋ions up to a fluence of 1.45 ×10^16Kr^3＋/cm^2. Irradiation induced structural modifications are examined by using grazing incidence x-ray diffraction（GIXRD） and cross-sectional transmission electron microscopy（TEM）. The GIXRD reveals that amorphous fraction increases with the increase of fluences up to 2 × 10^15Kr^3＋/cm^2, and the results are explained with a direct-impact model.However, when the irradiation fluence is higher than 2 × 10^15Kr^3＋/cm^2, the amorphous fraction reaches a saturation of-80%. Further TEM observations imply that nano-crystal is formed with a diameter of -10 nm within the irradiation layer at a fluence of 4 × 10^15Kr^3＋/cm^2. No full amorphization is achieved even at the highest fluence of 1.45 × 10^16Kr^3＋/cm^2（-36 displacement per atom）. The high irradiation resistance of pyrochlore Lu2Ti2O7 at higher fluence is explained on the basis of enhanced radiation tolerance of nano-crystal structure.

AMORPHIZATION IN Nb-M (M=Fe, Co, Ni) BINARY METAL SYSTEMS INDUCED BY ION BEAM ASSISTED DEPOSITION (IBAD)

Ion beam assisted deposition technique (IBAD) was utilized to systematically study amorphization in binary metal systems of Nb-magnetic element, i.e., Nb-M (M=Fe, Co or Ni). The glass forming range termed as Nb fraction of Nb-Fe system was about 34at.% to 56at.%, that of Nb-Co system was about 32at.% to 72at.% and that of Nb-Ni about 20at. % to 80at. %. Similar percolation patterns were found in amorphous alloy films. The fractal dimensions of the percolation patterns approach to 2, which indicates 2-D layer growth for amorphous phases. It is regarded that the assisted Ar+ ion beam during the deposition process plays important role for the 2-D layer growth. Some metastable crystalline phases were obtained in these three systems by IBAD, e.g., bcc supersaturated solid solutions in Nb-Fe and Nb-Co systems, fcc and hcp phases in Nb-Co and Nb-Ni systems. The formation and competing between the amorphous and the metastable crystalline phases were determined by both the phases' thermodynamic states in binary metal systems and kinetics during IBAD process.

AMORPHIZATION TRANSFORMATION BY MECHANICAL ALLOYING IN THE Mo-Si SYSTEM

Starting from elemental powders, complete MoSi2 powder forms abruptly between 3.5and 4 h during mechanical alloying (MA) of the Mo-66 at.% Si powders. Continuous milling of this MoSi2 Phase leads to a nanocrystalline powder and amorphizationtransformation takes place after 100 h milling. Howeven MA of the Mo-37.5 at.%Si powders does not result in the formation of the Mo5Si3 crystalline phase, but the formation of a Mo(Si) supersaturated solid solution (SSS) and a completely amorphots phase after 5 h and 70 h milling, respectively. The free energy of the Mo-Sisystem has been calculated and it has been found that there is no driving force for the amorphization reaction under normal conditions. The amorphization by MA of the Mo-Si system is attributed to a solid-state amorphization reaction in which defects and a very fine grain size induced during milling process may raise the free energy of the crystalline intermetallic phase (for MoSi2) or the Mo(Si) supersaturated solid solution (for Mo5Si3) above that of the amorphous phase.

Formation of interfacial Al-Ce-Cu-W amorphous layers in aluminum matrix composite through thermally driven solid-state amorphization

Interfacial Al-Ce-Cu-W amorphous layers formed through thermally driven solid-state amorphization within the(W+Ce O2)/2024 Al composite were investigated.The elemental distributions and interfacial microstructures were examined with an electron probe microanalyzer and a high-resolution transmission electron microscope,respectively.The consolidation of composites consisted of two thermal processes:vacuum degassing(VD)and hot isostatic pressing(HIP).During consolidation,not only the three major elements(Al,W,and Ce)but also the alloying elements(Mg and Cu)in the Al matrix contributed to amorphization.At VD and HIP temperatures of 723 K and763 K,interfacial amorphous layers were formed within the composite.Three diffusion processes were necessary for interfacial amorphization:(a)long-range diffusion of Mg from the Al matrix to the interfaces during VD;(b)long-range diffusion of Cu from the Al matrix to the interfaces during HIP;(c)short-range diffusion of W toward the Al matrix during HIP.The newly formed interfacial Al-Ce-Cu-W amorphous layers can be categorized under the Al-Ce-TM(TM:transition metals)amorphous system.

Mechanically-driven Amorphization in Metallic Systems

The mechanism of mechanically-driven amorphization was extensively surveyed in various systems. It was concluded that the amorphization could occur in the systems of Cu-Zr with a negative heat of mixing (-ΔH) and Cu-Ta with a positive heat of mixing (+ΔH) by mechanical alloying of elemental powders.Such amorphization could also be started from an intermetallic compound Cu_xZr_y with no chemical reaction involved.The energy storage by mechanical attrition should be the driving force for the amorphization.The atomic distribution function and nuclear resonance spectroscopic studies show that the mechanical alloying provides a true alloying on an atomic level.The alloys formed are of a characteristic structure common to the rapidly quenched amorphous alloys.

Hydrogen-induced amorphization of Zr-Cu-Ni-Al alloy

Arc melting was utilized in this study to produce Zr_(55)Cu_(30)Ni_5Al_(10) alloys under mixed atmospheres with various ratios of high-purity hydrogen to argon. The influences of hydrogen addition on the solidification structure and glass-forming ability of Zr_(55)Cu_(30)Ni_5Al_(10) alloy were determined by examining microstructures in different parts of the cast ingots. The results showed that different degrees of crystallization structures were obtained in the ascast button ingots after arc melting in high-purity Ar, and the cross-sectional solidification morphology of arcmelted ingots was found to consist of crystals with varying from the bottom up. By contrast, there were completely amorphous structures in the middle and upper areas of the as-cast button ingots fabricated by adding 10% H_2 to the high-purity Ar atmosphere. A clear solidification interface was found between the crystal and glass in the ascast button ingots, which indicates that hydrogen addition can enhance the Zr_(55)Cu_(30)Ni_5Al_(10) alloy's glass-forming ability. The precise mechanism responsible for this was also investigated.

High-Pressure Irreversible Amorphization of La_1/3NbO₃

The crystallographic structure of La1/3NbO3 perovskite was studied at high pressures using a diamond-anvil cell and synchrotron radiation. High-pressure energy dispersive (EDS) x-ray diffraction and high-pressure angle dispersive (ADS) x-ray diffraction revealed an irreversible amorphization at ~10 GPa. A large change in the bulk modulus accompanied the high-pressure amorphization.

Amorphization and magnetic properties of Fe_(62)Nb_(38) mechanically alloyed powders

The amorphization and magnetic properties of Fe_(62)Nb_(38) mechanicallyalloyed powders were investigated. In the initial mechanical alloying processes, the latticestructure of pure Fe is destroyed due to the cold-welding and fracturing, accompanying the reductionof ferromagnetic properties. The M_S value of Fe_(62)Nb_(38) powders with ball-milling time t = 6 his only 48.1 A·m^2/kg. With prolongating of mechanical alloying processes, a solid stateamorphization reaction (SSAR) takes place and the Fe-Nb ferromagnetic amorphous phase is formed.With the milling time increasing from 6 to 18 h, the saturation magnetization of Fe_(62)Nb_(38)powders increases with enhancement of the proportion of ferromagnetic amorphous phase in milledpowders. The M_S value of the Fe_(62)Nb_(38) amorphous powders is 98 A·m^2/kg, which is very closeto the value estimated from dilute model. However, the Curie temperature of the Fe_(62)Nb_(38)amorphous phase is only 206℃, which is much smaller than that of the pure Fe. This implies that theexchange interaction between Fe atoms in amorphous alloyed Fe_(62)Nb_(38) becomes weak due to theNb dilution. Investigation shows that the variation of magnetic properties of milled powders is oneof important tools for describing the amorphization by mechanical alloying.

SOLED STATE AMORPHIZATION REACTION REACTION UNDER HIGH PRESSURE

The solid state reaction of Nigo Tigo multilayer under high pressure was carried out to investigate the effect of pressure on the amorphization process.Under the pressure of BOkbars amorphization reaction could not occur at 250℃while amorphous phase formed by isothermal annealing at same temperature in vacuum as well as lower pressure.It is suggested that the effect of pressure on diffusion played a predominant role,and Ni atom should diffuse into Ti layers with vacancy mechanism rather than interstitial one.

Atomistic Investigation of Shock-Induced Amorphization within Micro-shear Bands in Hexagonal Close-Packed Titanium

The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At high strain rates,amorphization occurred near the edge of the contact region where severe shear strain induced a large number of stacking faults(SFs)and dislocations.In contrast,the central part of the contact region underwent less deformation with significantly fewer dislocations.Moreover,instead of amorphization by consuming SFs and dislocations,there was a gradual increase in the density of dislocations and SFs during the process of amorphization.These local amorphous regions eventually grew into shear bands.

Crystalline-amorphization-recrystallization structural transition and emergent superconductivity in van der Waals semiconductor SiP under compression

van der Waals(vdW)semiconductors have gained significant attention due to their unique physical properties and promising applications,which are embedded within distinct crystallographic symmetries.Here,we report a pressure-induced crystallineamorphization-recrystallization transition under compression in binary vdW semiconductor SiP.Upon compression to 52 GPa,bulk SiP undergoes a consecutive phase transition from pristine crystalline to amorphous phase,ultimately to recrystallized phase.By employing synchrotron X-ray diffraction experiments in conjunction with high-pressure crystal structure searching techniques,we reveal that the recrystallized Si P hosts a tetragonal structure(space group I4mm)and further transforms partially into a cubic phase(space group Fm3m).Consistently,electrical transport and alternating-current magnetic susceptibility measurements indicate the presence of three superconducting phases,which are embedded in separate crystallographic symmetries—the amorphous,tetragonal,and cubic structures.Furthermore,a high superconducting transition temperature of 12.3 K is observed in its recovered tetragonal phase during decompression.Our findings uncover a novel phase evolution path and elucidate a pressure-engineered structure-property relationship in vdW semiconductor SiP.These results not only offer a new platform to explore the transformation between different structures and functionalities,but also provide new opportunities for the design and exploration of advanced devices based on vdW materials.

High-entropy(Sm_(0.2)Eu_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2))_(2)Hf_(2)O_(7) ceramic with superb resistance to radiation-induced amorphization

Nuclear engineering materials are required to possess outstanding extreme environmental tolerance and irradiation resistance.A promising novel pyrochlore-type of(Sm_(0.2)Eu_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2))2 Hf_(2)O_(7)high-entropy ceramic(HE-RE2 Hf_(2)O_(7))for control rod was prepared by solid-state reaction method.The ion irradiation of HE-RE_(2) Hf_(2)O_(7)with 400 keV Kr+at 400℃was investigated using a 400 kV ion implanter and compared with single-component pyrochlore Gd2 Hf_(2)O_(7)to evaluate the irradiation resistance.For HE-RE2 Hf_(2)O_(7),the phase transition from pyrochlore to defective fluorite is revealed after irradiation at 60 dpa.After irradiation at 120 dpa,it maintained crystalline,which is comparable to Gd2 Hf_(2)O_(7)but superior to the titanate pyrochlores previously studied.Moreover,the lattice expansion of HE-RE2 Hf_(2)O_(7)(_(0.2)2%)is much lower than that of Gd2 Hf_(2)O_(7)(0.62%),indicating excellent irradiation damage resistance.Nanoindentation tests displayed an irradiation-induced increase in hardness and a decrease in elastic modulus by about 2.6%.Irradiation-induced segregation of elements is observed on the surface of irradiated samples.In addition,HE-RE2 Hf_(2)O_(7)demonstrates a more sluggish grain growth rate than Gd2 Hf_(2)O_(7)at 1200℃,suggesting better high-temperature stability.The linear thermal expansion coefficient of HE-RE2 Hf_(2)O_(7)is 10.7×10-6 K-1 at 298–1273 K.In general,it provides a new strategy for the design of the next advanced nuclear engineering materials.

Ultra-fast amorphization of crystalline alloys by ultrasonic vibrations

The amorphization of alloys is of both broad scientific interests and engineering significance.Despite considered as an efficient strategy to regulate and even achieve record-breaking properties of metallic materials,a facile and rapid method to trigger solid-state amorphization is still being pursued.Here we report such a method to utilize ultrasonic vibration to trigger amorphization of intermetallic compound.The ultrasonic vibrations can cause tunable amorphization at room temperature and low stress(2 MPa)conveniently.Remarkably,the ultrasonic-induced amorphization could be achieved in 60 s,which is 360 times faster than the ball milling(2.16×10^(4) s)with the similar proportion of amorphization.The elements redistribute uniformly and rapidly via the activated short-circuit diffusion.Both experimental evidences and simulations show that the amorphous phase initiates and expands at nanograin boundaries,owing to the induction of lattice instability.This work provides a groundbreaking strategy for developing novel materials with tunable structures and properties.

Borohydride Ammoniate Solid Electrolyte Design for All-Solid-State Mg Batteries

Searching for novel solid electrolytes is of great importance and challenge for all-solid-state Mg batteries.In this work,we develop an amorphous Mg borohydride ammoniate,Mg(BH_(4))_(2)·2NH_(3),as a solid Mg electrolyte that prepared by a NH_(3)redistribution between 3D framework-γ-Mg(BH_(4))_(2)and Mg(BH_(4))_(2)·6NH_(3).Amorphous Mg(BH_(4))_(2)·2NH_(3)exhibits a high Mg-ion conductivity of 5×10^(-4)S cm^(-1)at 75℃,which is attributed to the fast migration of abundant Mg vacancies according to the theoretical calculations.Moreover,amorphous Mg(BH_(4))_(2)·2NH_(3)shows an apparent electrochemical stability window of 0-1.4 V with the help of in-situ formed interphases,which can prevent further side reactions without hindering the Mg-ion transfer.Based on the above superiorities,amorphous Mg(BH_(4))_(2)·2NH_(3)enables the stable cycling of all-solid-state Mg cells,as the critical current density reaches 3.2 mA cm^(-2)for Mg symmetrical cells and the reversible specific capacity reaches 141 mAh g^(-1)with a coulombic efficiency of 91.7%(first cycle)for Mg||TiS_(2)cells.

Quasi-plastic deformation mechanisms and inverse Hall-Petch relationship in nanocrystalline boron carbide under compression

Grain boundaries(GBs)play a significant role in the deformation behaviors of nanocrystalline ceramics.Here,we investigate the compression behaviors of nanocrystalline boron carbide(nB_(4)C)with varying grain sizes using molecular dynamics simulations with a machine-learning force field.The results reveal quasi-plastic deformation mechanisms in nB_(4)C:GB sliding,intergranular amorphization and intragranular amorphization.GB sliding arises from the presence of soft GBs,leading to intergranular amorphization.Intragranular amorphization arises from the interaction between grains with unfavorable orientations and the softened amorphous GBs,and finally causes structural failure.Furthermore,nB_(4)C models with varying grain sizes from 4.07 nm to 10.86 nm display an inverse Hall-Petch relationship due to the GB sliding mechanism.A higher strain rate in nB_(4)C often leads to a higher yield strength,following a 2/3 power relationship.These deformation mechanisms are critical for the design of ceramics with superior mechanical properties.

In Situ HRTEM Observation of Electron-Irradiation-Induced Amorphization and Dissolution of the E(Al_(18)Cr_2Mg_3) Phase in 7475 Al Alloy

Electron irradiation effects on phase stability of the E （Al18Cr2Mg3） phase have been investigated by high- angle annular dark-field scanning transmission electron microscopy and high-resolution transmission electron microscopy （HRTEM）. The in situ HRTEM observations show that the Ala8Cr2Mg3 particles with different thickness undergo amorphization and dissolution under 300 keV electron irradiation at 25 ℃. The results indicate that the intermetallic compound Al18Cr2Mg3 is unstable under electron irradiation, and structural changes mainly depend on the thickness of particles. Amorphization in the thick particles is caused by a combination of chemical disordering and an increase in point defect concentration. Dissolution after amorphization in the thin particles is attributed to the diffusion of point defect towards the Al matrix.