Evolution Of Short-range Order Research Articles

Green conversion of waste alkaline battery material to zeolitic imidazolate framework-8 and its iodine capture mechanism

Zeolitic imidazolate framework-8 (ZIF-8) exhibits excellent performance in capturing iodine. However, the solvent-based procedures and raw materials for ZIF-8 synthesis often lead to secondary pollution. We developed a solvent-minimizing method for preparing ZIF-8 via ball milling of raw material obtained from spent alkaline batteries, and studied its iodine-capture performance and structural changes. Exposure of the ZIF-8 to iodine vapor for 60 min demonstrated that it exhibited industrially competitive iodine-capture performance (the adsorbed amount reaches to 1123 mg g−1 within 60 min). Spectroscopic studies showed that ZIF-8 underwent a structural transformation upon iodine loading. Iodine molecules were adsorbed onto the surface of ZIF-8 and also formed C–I bond with the methyl groups on the imidazole rings, reducing iodine release. This work represents a comprehensive revelation of long-range order and short-range order evolution of ZIF-8 during iodine vapor adsorption over time. Moreover, this green synthesis of ZIF-8 is of lower cost and generates fewer harmful by-products than existing methods, and the produced ZIF-8 effectively entraps toxic iodine vapor. Thus, this synthesis enables a sustainable and circular material flow for beneficial utilization of waste materials.

Structural evolution of short-range order in CrCoNi and MnCoNi medium-entropy alloys

Structural evolution of short-range order in CrCoNi and MnCoNi medium-entropy alloys

Evolution of Short-Range Order of Amorphous GeTe Upon Structural Relaxation Obtained by TEM Diffractometry and RMC Methods.

Glasses frequently reveal structural relaxation that leads to changes in their physical properties including enthalpy, specific volume, and resistivity. Analyzing the short-range order (SRO) obtained from electron diffraction by transmission electron microscopy (TEM) in combination with Reverse-Monte-Carlo (RMC) simulations is shown to provide information on the atomic arrangement. The technique elaborated here features several benefits including reliability, accessibility, and allows for obtaining detailed structural data quickly. This is demonstrated with a detailed view of the structural changes in the as-deposited amorphous phase change material (PCM) GeTe. The data show a significant increase in the average bond angle upon thermal treatment. At the same time the fraction of tetrahedrally coordinated Ge atoms decreases due to an increase in octahedrally distorted and pyramidal motifs. This finding provides further evidence for the atomic processes that govern structural relaxation in amorphous GeTe and other PCMs. A thorough literature review finally unveils possible origins of the large discrepancies reported on the structure of amorphousGeTe.

Element-dependent evolution of chemical short-range ordering tendency of NiCoFeCrMn under irradiation

The evolution of short-range order (SRO) structures under irradiation has a great impact on the mechanical properties of high-entropy alloys. In this study, the atomistic mechanism of the evolution of SRO during and after cascade collisions was investigated in NiCoFeCrMn by multiscale modeling using molecular dynamics and lattice kinetic Monte Carlo simulations. SRO structures could be destructed by cascade collisions in short time and recovered by atomic diffusion in a much longer time. The destruction rate depends on the primary knock-on atom energies in cascade collisions and shows a universal law with respect to the number of replacement-per-atom. The vacancy diffusion simulations reveal that the SRO recovery rates of different element pairs vary significantly due to the distinct diffusion rates. Consequently, the SRO state under irradiation differs from that in thermodynamic equilibrium due to the difference of destruction and recovery rate for each element pair. The evolution of SRO is a result of the competition between the destruction and recovery mechanisms and depends heavily on the irradiation conditions.

Evolution of short-range order and its effects on the plastic deformation behavior of single crystals of the equiatomic Cr-Co-Ni medium-entropy alloy

Short-range ordering (SRO), its evolution in the equiatomic Cr-Co-Ni medium-entropy alloy (MEA), and its effects on mechanical properties were investigated by, respectively, electrical resistivity measurements and tension and compression tests on single crystal specimens at room temperature and liquid nitrogen temperature. SRO below 973 K can be monitored by changes in electrical resistivity, which increases gradually with time to a saturation value during isothermal annealing in the temperature range of 673–973 K. While the time required to reach saturation is shorter at higher temperatures, the saturation resistivity is higher at lower temperatures, indicating a higher degree of SRO at lower temperature although it takes longer to reach saturation because of slower kinetics. No significant change in the plastic deformation behavior is found at room temperature and 77 K for different degrees of SRO. The yield stress as well as the slip localization behavior are basically the same after SRO, and the magnitude of yield drop does not correlate with the degree of SRO. Tensile stress-strain curves are not much affected by SRO up to high strain levels, resulting in identical shear stresses for the onset of deformation twinning at room temperature regardless of the degree of SRO. The dislocation structure, variations in dislocation dissociation width, and stacking fault energy are all essentially unchanged.

Ultrafast atomic view of laser-induced melting and breathing motion of metallic liquid clusters with MeV ultrafast electron diffraction

Under the irradiation of an ultrafast intense laser, solid materials can be driven into nonequilibrium states undergoing an ultrafast solid-liquid phase transition. Understanding such nonequilibrium states is essential for scientific research and industrial applications because they exist in various processes including laser fusion and laser machining yet challenging in the sense that high resolution and single-shot capability are required for the measurements. Herein, an ultrafast diffraction technique with megaelectron-volt (MeV) electrons is used to resolve the atomic pathway over the entire laser-induced ultrafast melting process, from the initial loss of long-range order and the formation of high-density liquid to the progressive evolution of short-range order and relaxation into the metastable low-density liquid state. High-resolution measurements using electron pulse compression and a time-stamping technique reveal a coherent breathing motion of polyhedral clusters in transient liquid aluminum during the ultrafast melting process, as indicated by the oscillation of the interatomic distance between the center atom and atoms in the nearest-neighbor shell. Furthermore, contraction of interatomic distance was observed in a superheated liquid state with temperatures up to 6,000 K. The results provide an atomic view of melting accompanied with internal pressure relaxation and are critical for understanding the structures and properties of matter under extreme conditions.

Mean Free Path of Photoelectronic Excitations in Hydrogenated Amorphous Silicon and Silicon Germanium Alloy Semiconductors

Hydrogenated amorphous silicon germanium alloy (a‐Si1−x Ge x :H) films are prepared by plasma enhanced chemical vapor deposition (PECVD) and characterized by in situ real time spectroscopic ellipsometry (RTSE). From complex dielectric function spectra extracted, the broadening width energy (Γ) of the primary absorption feature centered near 3.7 eV is quantified using the Cody–Lorentz oscillator model. Mean free path length of photoelectronic excitations is calculated from Γ based on reasonable estimates for speed of electron–hole photoexcitations. A model is applied with excited state lifetime assumed to be limited by scattering from network disorder and provides a relative measure of short‐range order. The simple model applied is an extension of that widely used to characterize broadening of optical transitions in polycrystalline semiconductors. Decreases in mean free path of up to ∼30% occur with germanium. Relative increases in mean free path with increased hydrogen during PECVD a‐Si:H, a‐Si0.73Ge0.27:H, and a‐Si0.60Ge0.40:H occur from ∼5% to ∼8% and with hydrogen plasma treatment of a‐Si:H by ∼6%. Mean free path changes are tracked with thickness to provide short range order evolution and the effect of the underlying material. Mean free path of photoexcitations in electronic quality a‐Si1−x Ge x :H is estimated at ∼3.5 Å, on the same order as interatomic spacing.

Local Ordering Tendency in Body-Centered Cubic (BCC) Multi-Principal Element Alloys

The recent development of high-entropy alloys (HEAs) has opened a new avenue for alloy design by incorporating multiple principal elements into a simple crystal lattice. In HEAs, short-range chemical ordering may arise due to the different mixing properties of various constituent elements. In this work, we explore the trend of elemental arrangement in five typical body-centered cubic (BCC) multi-principal element alloys (MPEAs), including CrFeV, HfNbZr, TaVW, NbTaV, and TaTiV. Combining the Monte Carlo method and density-functional theory calculations, we calculated the evolution of short-range order (SRO) parameters in these alloys at 500 K. Our results demonstrated that all these MPEAs might develop a certain degree of SRO, depending on the mixing properties of different element pairs. Using a modified quasi-chemical model, we show that the SRO values in these MPEAs can be accurately predicted as long as the mixing enthalpy values between different atomic pairs are known. The presence of SRO has a profound impact on the local structure of MPEAs, which further alters the electronic and elastic properties of MPEAs. Our results provide a theoretical understanding of the basic alloy structure of novel MPEAs, which is an essential step toward tailoring their properties.

Dielectric and ferroelectric properties evolution of (1−x)(Bi0.5Na0.5TiO3)–xK0.5Na0.5NbO3 piezoceramics

In this work, piezoceramics of (1−x)(Bi0.5Na0.5)TiO3–x(K0.5Na0.5)NbO3, (1−x)BNT–xKNN, in the compositional range 0.00 ≤ x ≤ 0.07, were prepared by a mechanochemically activated solid-state method. The structural phase formation and microstructural, dielectric, and ferroelectric properties were studied. Although changes, in symmetry of the perovskite structure, were not detected with the composition (i.e., from a perspective of its intrinsic properties), the microstructural evolution was strongly dependent on the content of the KNN phase (i.e., based on its extrinsic properties). Specifically, KNN favoured the formation of a microstructure with cubic grains, typical morphology of the alkaline niobate ceramics. After KNN addition, both the maximum permittivity temperature and the long-range to short-range ordered transition temperature were reduced. Additionally, ferroelectric loops and strain deformation curves also reflect the long-range to short-range order evolution with KNN addition and temperature.

Short-Range Order Evolution in Nanocrystalline Mechanically Activated Fe–Cr Alloys in the Process of Annealing

Nanocrystalline Fe–Cr alloys synthesized from pure components in a planetary ball mill with a chromium content of 20–48 at % were annealed for 4 h at temperatures of Tan = 400–700°C. Short-range order (SRO) evolution and phase separation dependent on Tan were studied using Mossbauer spectroscopy and X-ray diffraction. The precipitation of the σ-FeCr phase was observed only in the samples with 48 at % of Cr at Tan = 600 and 700°C. For all the samples, the grain growth began most intensively from 400°C, and the higher the Cr content in an alloy, the smaller the final size of grains after Tan = 700°C. The analysis of behavior of the mean hyperfine field on Fe nuclei and distribution of the hyperfine field width depending on Tan, as well as fitting of Mossbauer spectra with spectral components corresponding to the α (Cr depleted) and α' (Cr rich) phases, demonstrated that the mechanically alloyed Fe-Cr samples were characterized by weak short-range separation passing at Tan = 400°C to a nearly statistically uniform distribution of atoms. Heterogeneous short-range order with the α and α' regions was formed in the alloys with 30 at % of Cr and more after annealing at 500–700°C. An analysis with the material balance equation led to our conclusion about the existence of the grain boundary segregations of Cr atoms.

Structural-Phase Transformations and Short-Range Order Evolution in the Fe–Cr System during Mechanical Alloying

Using Mossbauer spectroscopy on 57Fe nuclei and X-ray diffraction, the mechanism of mechanical alloying in a planetary ball mill of the Fe–Cr nanocrystalline system in a concentration range from 20 to 48 at % Cr has been studied in detail. It has been established that mechanical alloying occurs in one stage at a concentration of up to 30 at % Cr and in three stages at higher concentrations. The change in the mechanism of mechanical alloying occurs as iron is saturated with chromium and is caused by the inversion of the sign of the mixing energy from negative to positive.

Evolution of short-range order in chemically and physically grown thin film bilayer structures for electronic applications.

Functional thin films are commonly integrated in electronic devices as part of a multi-layer architecture. Metal/oxide/metal structures e.g. in resistive switching memory and piezoelectric microelectrochemical devices are relevant applications. The films are mostly fabricated from the vapour phase or by solution deposition. Processing conditions with a limited thermal budget typically yield nanocrystalline or amorphous layers. For these aperiodic materials, the structure is described in terms of the local atomic order on the length scale of a few chemical bonds up to several nanometres. Previous structural studies of the short-range order in thin films have addressed the simple case of single coatings on amorphous substrates. By contrast, this work demonstrates how to probe the local structure of two stacked functional layers by means of grazing incidence total X-ray scattering and pair distribution function (PDF) analysis. The key to separating the contributions of the individual thin films is the variation of the incidence angle below the critical angle of total external reflection, In this way, structural information was obtained for functional oxides on textured electrodes, i.e. PbZr0.53O0.47O3 on Pt[111] and HfO2 on TiN, as well as HfO2-TiOx bilayers. For these systems, the transformations from disordered phases into periodic structures via thermal teatment are described. These examples highlight the opportunity to develop a detailed understanding of structural evolution during the fabrication of real thin film devices using the PDF technique.

Evolution of short range order in Ar: Liquid to glass and solid transitions–A computational study

The evolution of the short range order (SRO) as a function of temperature in a Lennard-Jones model liquid with Ar parameters was determined and juxtaposed with thermodynamic and kinetic properties obtained as the liquid was cooled (heated) and transformed between crystalline solid or glassy states and an undercooled liquid. The Lennard-Jones system was studied by non-equilibrium molecular dynamics simulations of large supercells (approximately 20000 atoms) rapidly cooled or heated at selected quenching rates and at constant pressure. The liquid to solid transition was identified by discontinuities in the atomic volume and molar enthalpy; the glass transition temperature range was identified from the temperature dependence of the self-diffusion. The SRO was studied within the quasi-crystalline model (QCM) framework and compared with the Steinhardt bond order parameters. Within the QCM it was found that the SRO evolves from a bcc-like order in the liquid through a bct-like short range order (c/a=1.2) in the supercooled liquid which persists into the glass and finally to a fcc-like ordering in the crystalline solid. The variation of the SRO that results from the QCM compares well with that obtained with Steinhardt’s bond order parameters. The hypothesis of icosahedral order in liquids and glasses is not supported by our results.

Comparative study of crystallization process in metallic melts using ab initio molecular dynamics simulations

The crystallization process of liquid metals is studied using ab initio molecular dynamics simulations. The evolution of short-range order during quenching in Pb and Zn liquids is compared with body-centered cubic (bcc) Nb and V, and hexagonal closed-packed (hcp) Mg. We found that the fraction and type of the short-range order depends on the system under consideration, in which the icosahedral symmetry seems to dominate in the body-centered cubic metals. Although the local atomic structures in stable liquids are similar, liquid hcp-like Zn, bcc-like Nb and V can be deeply supercooled far below its melting point before crystallization while the supercooled temperature range in liquid Pb is limited. Further investigations into the nucleation process reveal the process of polymorph selection. In the body-centered cubic systems, the polymorph selection occurs in the supercooled state before the nucleation is initiated, while in the closed-packed systems it starts at the time of onset of crystallization. Atoms with bcc-like lattices in all studied supercooled liquids are always detected before the polymorph selection. It is also found that the bond orientational ordering is strongly correlated with the crystallization process in supercooled Zn and Pb liquids.

Thermally induced failure mechanism transition and its correlation with short-range order evolution in metallic glasses

The effect of temperature on the short-range order (SRO) structures, deformation mechanisms and failure modes of metallic glasses (MGs) is of fundamental importance for their practical applications. However, due to lack of direct structural information at the atomistic level from experiments and the absence of previous molecular dynamics (MD) simulations to reproduce experimental observations over a wide range of temperature, this issue has not been well understood. Here, by carefully constructing the atomistic models of Cu64Zr36 and Fe80W20 MGs, we are able to reproduce the major deformation modes observed experimentally, i.e. single shear banding (SB) at low temperatures, multiple shear-bandings at intermediate temperatures and homogeneous plastic flow at elevated temperatures. By examining the evolution of SRO, we find that the different failure modes exhibit distinctively different full-icosahedron (FI) evolution pathways at different temperatures. Specifically, at low temperatures, the FI concentration first deceases to a minimum, then recovers slightly, and finally comes to a plateau; at intermediate temperatures, it first decreases and then reaches a plateau; while at elevated temperatures, it decreases simply monotonically. These different pathways arise from the dynamic competition between the destruction and recovering of FI clusters. We further show that the local softening caused by the destructions of FI clusters is crucial for the formation of localized shear planes and further shear bands. Since our simulations exhibit the same trend for both MG systems, it is expected that these findings may be generic for a wide range of MGs.

The crystallization process of liquid vanadium studied by ab initio molecular dynamics

We present a study of the crystallization process in liquid vanadium over a temperature range from 3000 K down to 1500 K using ab initio molecular dynamics simulations. Short-range order evolution during solidification is studied using various structural analysis methods. We show that the icosahedral-like short-range order is detected in the stable liquid phase and grows upon supercooling. The system undergoes a first-order phase transition (from a liquid to a solid state) at a temperature of about 1600 K. The crystal nucleation process is further studied using the time–temperature transformation mechanism by annealing the system at 1650 K. The nucleation is examined using bond-orientational order and density fluctuation analysis. Our finding is that various precursors appear in the region of high bond-orientational order with the majority having body-centered cubic (bcc)-like symmetry. This bcc-like region grows on annealing via thermal fluctuations. Our results reveal that the bond-orientational order precedes the density fluctuation, and is the main driving factor for nucleation.

Ab initio molecular dynamics simulation of binary Ni62.5Nb37.5 bulk metallic glass: validation of the cluster-plus-glue-atom model

We have performed ab initio molecular dynamics simulation of Ni62.5Nb37.5 alloy at descending temperatures (from 1800 to 300 K) and discussed the evolution of short-range order with temperature. The pair-correlation functions, coordination numbers, and chemical compositions of the most abundant local clusters have been analyzed. We found that icosahedral short-range order exists in the liquid, undercooled, and amorphous states, and it becomes dominant in the amorphous states. Moreover, we demonstrated the existence of Ni-centered Ni7Nb6 icosahedral clusters as the major local structural unit in the Ni62.5Nb37.5 amorphous alloy. This finding agrees well with our previous “cluster-plus-glue-atom” model for the Ni–Nb bulk metallic glasses. The positions of the first peaks of Ni–Nb pair correlation functions are lower than the sum of the metallic radii of Ni and Nb, suggesting enhanced chemical bonding between Ni and Nb atoms in Ni62.5Nb37.5 alloy. Analysis of electronic structures further revealed that the Nb-to-Ni charge transfer is responsible for the enhanced Ni–Nb bonding.

Ab initio molecular dynamics simulation of binary Cu64Zr36 bulk metallic glass: Validation of the cluster-plus-glue-atom model

We have performed ab initio molecular dynamics simulation of Cu64Zr36 alloy at descending temperatures (from 2000 K to 400 K) and discussed the evolution of short-range order with temperature. The pair-correlation functions, coordination numbers, and chemical compositions of the most abundant local clusters have been analyzed. We found that icosahedral short-range order exists in the liquid, undercooled, and glass states, and it becomes dominant in the glass states. Moreover, we demonstrated the existence of Cu-centered Cu8Zr5 icosahedral clusters as the major local structural unit in the Cu64Zr36 amorphous alloy. This finding agrees well with our previous cluster model of Cu-Zr-based BMG as well as experimental evidences from synchrotron x ray and neutron diffraction measurements.

Chemical and topological short-range order evolution of Mg65Cu25Gd10 alloy in the process of rapid solidification

The structural evolution of Mg65Cu25Gd10 alloy from liquid to glass state was investigated by ab initio molecular dynamics simulations. From 500 K, the splitting of the second peaks of the three partial pair correlation functions related to Mg has been perceived which implicates that short-range order is strengthened owing to the atomic rearrangement during the quenching process; medium-range order up to 7.59 Å has been observed from gcc(r) curves. The Gd-centered Voronoi polyhedron with index of 〈 0, 1, 10, 5 〉 was observed to increase drastically to an extraordinary level as the melt transformed to glass at 500 K, suggesting that it plays important role to keep the amorphous system stable. The variation of diffusion coefficients indicates that the solidification occurred at the temperature between 750 and 500 K.

Short-range order evolution in S-rich Ge–S glasses by X-ray photoelectron spectroscopy

The structure of binary Ge x S 100 − x chalcogenide glasses (10 < x < 30) is determined by high-resolution X-ray photoelectron spectroscopy (XPS). On the basis of compositional dependence of fitting parameters for Ge and S core level XPS spectra, the ratio between edge- and corner-shared tetrahedra is determined. It is shown that short-range order of these glasses includes fragments of high-temperature crystalline form of GeS 2. When subjected to X-irradiation, the structure of investigated glasses appears to become more homogeneous than that of the as-prepared samples.