Medium-range Order Structure Research Articles

Transmittance enhancement of amorphous SiO2 via ultraviolet irradiation to eliminate atomic defects

Optical absorption defects seriously degrade the performance of amorphous-SiO2. Laser/UV conditioning (LC/UC) emerge as promising methods for defects elimination, yet its mechanism is still debated due to insufficient defect characterization methods. In this study, the experiments and machine learning potential were used to characterize the defects in Raman, phonon/vibrational density of states, and XRD spectra, the UC mechanism was implied. The UC transforms the atomic defects into medium-range order structure (n-fold rings) to reduce the absorption, the mobile oxygen O0 reduces the energy barrier in the reaction and shorter wavelength of UC is suggested. Experimental results validated that the absorption coefficient below 300 nm after 254 nm UC decreases 62% higher than that after 365 nm UC.

Influence of Zr element on the atomic structure of Al-Cu alloy liquid

The relationship among chemical composition, structure and glass-forming ability in multicomponent alloys is a long-standing puzzle due to the complexity of compositions. In this work, Al77.8Cu22.2 and Al70Cu20Zr10 amorphous alloy liquids were investigated by combining high-energy X-ray diffraction at a synchrotron facility, ab-initio molecular dynamics and reverse Monte Carlo simulations. The analysis of short- and medium-range order structures of two liquid alloys show that the addition of Zr element increases the number of cluster types and makes the distribution of cluster content more uniform, and enhances the structural heterogeneity and correlation of clusters with high five-fold symmetry. These findings reveal the influence of Zr element on the atomic structure of the Al-Cu liquid alloy and deepen the understanding of Al-based metallic glasses formation.

Revealing in situ stress-induced short- and medium-range atomic structure evolution in a multicomponent metallic glassy alloy

Deformation behaviour of multicomponent metallic glasses are determined by the evolution/reconfiguration of the short- and medium-range order (SRO and MRO) atomic structures. A precise understanding of how different atom species rearrange themselves in different stress states is still a great challenge in materials science and engineering. Here, we report a systematic and synergetic research of using electron microscopy imaging, synchrotron X-ray total scattering plus empirical potential structure refinement (EPSR) modelling to study in situ the deformation of a Zr-based multicomponent metallic glassy alloy with 5 elements. Systematic and comprehensive analyses on the characteristics of the SRO and MRO structures in 3D and the decoupled 15 partial PDFs at each stress level reveal quantitatively how the SRO and MRO structures evolve or reconfigure in 3D space in the tensile and compressive stress states. The results show that the Zr-centred atom clusters have low degree of icosahedra and are the preferred atom clusters to rearrange themselves under the tensile and compressive stresses. The Zr-Zr is the dominant atom pair in controlling the shear band's initiation and propagation. The evolution and reconfiguration of the MRO clusters under different stress states are realised by changing the connection modes between the Zr-centred atom clusters. The coordinated changes of both bond angles and bond lengths of the Zr-centred clusters are the dominant factors in accommodating the tensile or compressive strains. While other solute-centred MRO clusters only play minor roles in the atomic structure reconfiguration/evolution. The research has demonstrated a synergetic and multimodal materials operando characterization methodology that has great application potential in design and development of high performance multiple-component engineering alloys.

Medium-range order structure analysis of metallic glasses based on reverse Monte Carlo modeling

The elucidation of amorphous alloy characteristics presents a formidable challenge due to the absence of crystalline arrangements and enigmatic imperfections. This study aimed to tackle this challenge through a comprehensive investigation utilizing synchrotron X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), ab initio molecular dynamics (AIMD) simulations, and reverse Monte Carlo (RMC) modeling. The primary objective was to delve into the medium range order (MRO) structure of metallic glasses (MGs) containing CuXZr100-X, wherein X represents values of 50, 56, 60, and 64. The results obtained from this research demonstrate that an increase in the Cu atom concentration within Cu-Zr MGs leads to the formation of complete icosahedral clusters and high-coordination polyhedral connections, thereby bolstering the stability and heterogeneity of local structures. Examination of the stiff full icosahedral bones shows that defects exist in the network connections on the MRO, resulting in a lack of connectivity in the positive icosahedron. Conversely, the density of defects decreases with an increase in Cu content. The observation suggests that the observed low MRO defects in Cu64Zr36 MGs may be accountable for their excellent glass-forming ability and kinetic stability.

Fabrication of Ni–Mo–Nb metallic glass/micro-nano lattice composite for nonenzymatic glucose sensing

The rising global diabetic population has ignited significant interest in enzyme-free electrochemical glucose sensors. However, their widespread usage has been severely impeded by the lack of sensing probes with both high sensitivity and stability. In this work, we present a novel approach for conformally depositing a Ni–Mo–Nb metallic-glass film onto a three-dimensional printed polymer skeleton for glucose detection. The printing template is designed based on a six-membered tricapped trigonal prism (6M-TTP) structure, which is derived from a medium-range order structure motif observed in amorphous alloys. The fabricated composite combines the high electrochemical activity of Ni–Mo–Nb amorphous alloy with the stability afforded by the micro-nano lattice structure, resulting in a high sensitivity (482 ​μA mM−1cm−2), a wide linear range (0–1 ​mM and 1–5 ​mM), a low detection limit (2.94 ​μM), and good long-term stability and selectivity in alkaline solution. Our work has proposed a new avenue to fabricate complex micro-nano electrodes, potentially offering significant versatility and great promise for widespread applications in the field of electrochemistry.

Medium-Range Order Structure Controls Thermal Stability of Pores in Zeolitic Imidazolate Frameworks.

Metal-organic framework (MOF) glasses have multiple potential applications, as they combine advantages of traditional glasses with those of MOFs. The melt-quenching process used to form MOF glasses typically leads to a significant decrease in porosity, but the structural origin of this thermally induced pore collapse remains largely unknown. Here, we study the melting process of three zeolitic imidazolate frameworks (ZIFs), namely ZIF-4, ZIF-62, and ZIF-76, using ab initio molecular dynamics (MD) simulations. By analyzing the MD data using topological data analysis, we show that while the three ZIF systems exhibit similar short-range order structural changes upon heating, they exhibit significant differences in their medium-range order structure. Specifically, ZIF-76 retains more of its medium-range order structures in the liquid state compared to the other glass-forming ZIF systems, which allows it to remain more porous than ZIF-4 and ZIF-62. As such, our results may aid in understanding the structural features that govern the ability to maintain porosity in the melt-quenched glassy state.

Short- and medium-range structure synergistically control fracture toughness of densified aluminoborate glasses

Methods to improve the fracture toughness of oxide glasses are needed since low fracture toughness is a major bottleneck for their applications. To overcome this, it is critically important to investigate the effect of both short- and medium-range structural features on fracture toughness. Recent work reported a record-high fracture toughness for a bulk lithium aluminoborate glass subjected to hot compression. Here, we further explore the structural origin of this high fracture toughness by subjecting different alkali aluminoborate glasses to hot compression. Through a combination of x-ray total scattering experiments and atomistic simulations, we find that hot compression causes significant changes to both the short- and medium-range order structure of the glasses, e.g., increased coordination numbers (CNs) of network forming species and decreased average size of ring-type structures. To this end, we reveal positive correlations between the pressure-induced increase in fracture toughness and (i) the increase in average CN of network forming species and (ii) the area of the first sharp diffraction peak in the structure factor. Our study thus improves the understanding of which structural features benefit intrinsic toughening of oxide glasses.

Revealing the relationship between liquid fragility and medium-range order in silicate glasses

Despite decades of studies, the nature of the glass transition remains elusive. In particular, the sharpness of the dynamical arrest of a melt at the glass transition is captured by its fragility. Here, we reveal that fragility is governed by the medium-range order structure. Based on neutron-diffraction data for a series of aluminosilicate glasses, we propose a measurable structural parameter that features a strong inverse correlation with fragility, namely, the average medium-range distance (MRD). We use in-situ high-temperature neutron-scattering data to discuss the physical origin of this correlation. We argue that glasses exhibiting low MRD values present an excess of small network rings. Such rings are unstable and deform more readily with changes in temperature, which tends to increase fragility. These results reveal that the sharpness of the dynamical arrest experienced by a silicate glass at the glass transition is surprisingly encoded into the stability of rings in its network.

Persistent homology: A tool to understand medium-range order glass structure

Glass structure remains puzzling to scientists, especially due to the challenges in characterizing their structural order beyond the first coordination shell, i.e., the so-called medium-range order. Structural method development is therefore needed to advance our understanding of, e.g., structure-property relations in these disordered materials. To this end, we here review the fundamentals, applications and perspectives of an interesting new approach, namely persistent homology , which is a type of topological data analysis. This method allows for the analysis of both ring- and void-type structures in materials without making any assumptions of the network structure. As discussed herein, it has recently been used to analyze atomic position data (as obtained from atomistic simulations or reverse Monte Carlo) of glasses, especially regarding their medium-range order structure. We also discuss the opportunities in coupling persistent homology analyses with machine learning calculations as well as the open questions and challenges that require further investigations. • We provide an introduction to the use of persistent homology. • Recent uses of persistent homology in glass science are reviewed. • Perspectives on applying persistent homology in glass science are identified.

Fabricating polymer/HEA-hybrid topological lattice structure for enhanced mechanical properties

Metamaterials such as architected lattice structures have aroused broad interest in being applied as mechanical supports for their lightweight and custom-shaped capabilities. Although various prior efforts have been devoted, a multiscale fabrication of micro-nano lattice structures without penalizing the mechanical properties is still a challenging but highly desirable task. Here we put forward a strategy to produce a mechanically enhanced micro-nano lattice structure by conformally depositing a CoCrFeNiTi high-entropy alloy (HEA) coating layer onto a three-dimensional (3D) printed polymer skeleton. The template for the 3D printing employs a six-membered tricapped trigonal prism (6M-TTP) structure derived from a medium-range order structure motif in amorphous alloys. The topological complexity of the 6M-TTP can substantially avoid the stress concentration by offering stress-release channels, while the HEA film incorporating with amorphous and nanocrystalline constituents can further reinforce the lattice architecture through its size hardening effect. Benefitting from the above, the fabricated polymer/HEA-hybrid lattice exhibits a high specific compressive strength (∼0.055 ​MPa ​kg-1 m3 at a density below 500 ​kg ​m-3), a superior elastic recoverability (∼70% recovery rate under >30% compression), an enhanced plasticity (40% strain) and a high specific modulus (0.135 ​MPa ​kg-1 m3). Our strategy initiates a perspective way to fabricate multiscale micro-nano lattice structures with improved mechanical properties, which could be extended to widespread metamaterial research.

Liquid-liquid transition and inherited signatures in Zr-Cu-Ni-Al metallic glasses

Up to now, the research of liquid-liquid transition (LLT) has significantly improved the understanding of its liquid structure and evolution, which is crucial to addressing the longstanding problem with glass formation. However, it remains unclear how LLT affects the vitrification and structures of glasses, due to the challenge in experimentally exploring LLT in high-temperature melt well above the liquidus temperature. In the present study, an experiment is conducted to observe LLT in three Zr-Cu-Ni-Al melts at around 1450 K from both dynamic and thermodynamic perspectives. It is discovered that superheated fragility is closely associated with glass-forming ability. By controlling the melt temperature, two types of metallic glasses are obtained, showing difference in crystallization behaviors, which is attributed to the competition between crystal-like clusters and icosahedral-like clusters. Prior to the LLT, the formation of crystal-like clusters is dominant. Afterwards, the LLT promoted formation of icosahedral-like clusters becomes dominant. Due to the inherited signatures in glass, LLT is manifested by the changes in both medium-range order structure and short-range order structure. This study further reveals the pattern of microstructural evolution accompanied by LLT in high-temperature multi-component melts, which is conducive to the control on structure and properties of glasses from liquids.

Structure dependence of fracture toughness and ionic conductivity in lithium borophosphate glassy electrolytes for all-solid-state batteries

Glass materials are potential candidates as solid electrolytes for batteries, but the atomistic origins of the variations in their properties and functionalities with composition are not well understood. Here, based on combined experimental and simulation techniques, we investigate the structural origin of the variation in fracture toughness and ionic conductivity of lithium borophosphate glass electrolytes with varying compositions. We focus on these properties since they are critically important for mechanical stability and electrochemical performances of glassy electrolytes. To this end, we have performed molecular dynamics simulations combined with X-ray total scattering experiments to provide the atomic picture of the disordered structure of borophosphate glass. The mechanical properties have been characterized through single-edge precracked beam measurements and axial tensile simulations. We find that the deformation and fracture behaviors of the electrolytes are governed by bond switching events of boron, which dissipate the strain energy during fracture. The migration of lithium ions in the electrolyte network is facilitated by hopping between superstructural rings, which reflects the important role of medium-range order structure in determining the lithium-ion diffusion. These findings have important implications for the design of future glassy electrolytes.

Outside-in disintegration of medium-range order in nano metallic glasses during torsion deformation revealed by molecular dynamics simulations

Medium-range order (MRO) is a substantial structure unit in understanding the structural characteristics, properties, and yield mechanism of amorphous solids. In this work, the evolution of MRO structures in nano metallic glasses under torsion deformation was studied by using molecular dynamics simulations. Upon torsion deformation, an interesting outside-in disintegration of MROs was detected, with most of the reduced icosahedral clusters in MRO structures transforming into other types of clusters while few of them become disconnected and turn into isolated icosahedral clusters. In addition, the proportion of face or volume-sharing icosahedra decreases, while the proportion of vertex or edge-sharing icosahedra increases. Specially, the average number of nearest neighboring icosahedra of <0,0,12,0> clusters also decreases. It was revealed that the significantly heterogeneous distribution of local shear stress was responsible for the outside-in disintegration of MROs, with a stress threshold for degradation of about 1.9 GPa.

Medium-range order structure of FeNiGaB alloys with good soft magnetic properties

In this paper, Fe40Ni38Mo4B18 and Fe40Ni38GaxB22-x (x=4, 6, 8 and 10) ribbons have been fabricated using the melt spinning method, and the effects of annealing temperature on the microstructure and magnetic properties have been investigated. Unlike the coarse grains of γ-(Fe, Ni) phase in annealed Fe40Ni38Mo4B18 ribbon, extremely refined nanostructure was found in the annealed Fe40Ni38GaxB22-x (x=4, 6, 8 and 10) ribbons, owing to that the charge transfer between Fe, Ni and Ga raised the binding forces of the atoms and thus greatly inhibited atoms diffusion. The novel nanostructure was identified as a single γ-(Fe, Ni, Ga) phase, in which a medium-range order structure and the conventional nano-grains were formed together. The soft magnetic properties were improved due to the grain refinement. Besides, the formation of the medium-range order structure in the alloys could have the great potential to inhibit the influence of the aging process on the soft magnetic properties.

A universal dimensionless length scale in medium range order amorphous structures

Our theoretical analysis reveals the existence of a previously unknown universality, namely, a dimensionless length scale, related to a ratio of medium and short range order structures of amorphous systems that originates from a conspiracy between dispersion forces among molecules and their phonon mediated coupling. The scale in turn gives rise to the structure lying underneath the low temperature universalities of many other properties e.g. specific heat, internal friction, boson peak characteristics, Meissner–Berret ratio etc.

BELLO: A post-processing tool for the local-order analysis of disordered systems

The characterization of the atomic structure of disordered systems, such as amorphous, glasses and (bio)molecule in solution, is a fundamental step for most theoretical investigations. The properties of short- and medium-range local order structures are responsible for the electronic, optical and transport properties of these systems. Here, we present the BELLO open source code, a post-processing script-tool created for the automatic analysis and extraction of structural characteristics of disordered and amorphous systems. BELLO is agnostic to the code that generated single configurations or trajectories, it provides an intuitive access through a graphical user interface (GUI), and it requires minimal computational resources. Its capabilities include the calculation of the order parameter q, the folded structure identification, and statistical analysis tools such as atomic coordination number and pair/angle-distribution functions. The working principles of the code are described and tested on ab initio molecular dynamics trajectories of amorphous chalcogenides.

Hot-melt extrudability of amorphous solid dispersions of flubendazole-copovidone: An exploratory study of the effect of drug loading and the balance of adjuvants on extrudability and dissolution

The FDA-approved anthelmintic flubendazole has shown potential to be repositioned to treat cancer and dry macular degeneration; however, its poor water solubility limits its use. Amorphous solid dispersions may overcome this challenge, but the balance of excipients may impact the preparation method and drug release. The purpose of this study was to evaluate the influence of adjuvants and drug loading on the development of an amorphous solid dispersion of flubendazole-copovidone by hot-melt extrusion. The drug, copovidone, and adjuvants (magnesium stearate and hydroxypropyl cellulose) mixtures were statistically designed, and the process was performed in a twin-screw extruder. The study showed that flubendazole and copovidone mixtures were highly extrudable, except when drug loading was high (>40%). Furthermore, magnesium stearate positively impacted the extrusion and was more effective than hydroxypropyl cellulose. The extruded materials were evaluated by modulated differential scanning calorimetry and X-ray powder diffraction, obtaining positive amorphization and physical stability results. Pair distribution function analysis indicated the presence of drug-rich domains with medium-range order structure and no evidence of polymer-drug interaction. All extrudates presented faster dissolution (HCl, pH 1.2) than pure flubendazole, and both adjuvants had a notable influence on the dissolution rate. In conclusion, hot-melt extrusion may be a viable option to obtain stable flubendazole:copovidone amorphous dispersions.

Unveiling the role of Y content in glass-forming ability and soft magnetic properties of Co-Y-B metallic glasses by experiment and ab initio molecular dynamics simulations

The effects of Y content on glass-forming ability (GFA) and soft magnetic properties of Co75-xYxB25 (x = 0, 3.5, 5) metallic glasses (MGs) were investigated by experiment and ab initio molecular dynamics (AIMD) simulations, and the relationship between local atomic structures and properties was discussed. The GFA and magnetic softness of Co75B25 alloy are improved by 3.5 at.% Y addition in our experiment. By calculating the local atomic structures (pair distribution function, coordination numbers, chemical short-range order, Voronoi polyhedron, structure factor, and the ratio of voids), dynamic behavior, electronic structure, magnetic moment, and magnetic anisotropy energy (MAE), we have found that the local atomic structures of Co-Y-B MGs are dominated by the B-centered prism units, and Y plays a vital role in the formation of the densely packed structures. In particular, the strongest chemical affinity of B-B, Co-Y, and B-Y pairs in Co71.5Y3.5B25 alloy is the critical factor for enhancing GFA and magnetic softness, which improves the degree of atomic packing in the first shell, the viscosity of supercooling melts, the stability of the local atomic structures, and reduces the MAE of the system. However, the excessive addition of Y (5 at.%) leads to a reduction of the GFA and magnetic softness, which may contribute to the highest fraction of deformed body-centered cubic (bcc) structures and the largest size of the medium-range order (MRO) structure in Co70Y5B25 alloy. This study shows a valuable perspective to understand the correlation between local atomic structures and properties of Co-based MGs, and also provides ideas for designing high-performance soft-magnetic MGs.

The role of TCP structures in glass formation of Ni50Ag50 alloys

A molecular dynamics simulation of rapid cooling at a cooling rate of 1011 K/s for Ni50Ag50 alloys was conducted. The rapid cooling process was analyzed by using the system energy, the pair distribution function, and the largest standard cluster analysis. It is found that with a crystallization-like energy curve the solidification of Ni50Ag50 alloy experiences a liquid-liquid and a liquid-solid transition (LLT and LST), finally result in an amorphous solid. In LLT stage the topologically close-packed (TCP) short-range order structures of both crystal (S666) and glass (S555) increase; whereas only glass medium-range order structures are formed. TCP-based long-range order (LRO) structures of glass do not increase until the beginning of the LST. Even in solid (T < Tg) the LRO parameter based on ICO structures fluctuates violently, while that based on TCP structures is quite stable. Therefore, TCP not only is the basic structural characteristics of disordered system but also reasonably represents the metastability of metallic glasses. These findings not only clarify the importance of LLT for the glass forming ability of alloys, but also fully demonstrate the effectiveness and necessity of TCP structures for describing the structure of amorphous systems.

Connecting short-range order for the liquid-solid transition of Al-Cu-Fe alloys

Liquid-solid transition processes have always been mysterious, especially those with the participation of quasicrystal (QC) structures, and are generally far less understood than the conventional solidification process. Here, the liquid structure variation of ternary QC-forming Al60Cu37Fe3 with crystal-forming Al50Cu40Fe10 alloy liquids was compared using synchrotron radiation based on high-energy X-ray diffraction (HE-XRD) and reverse Monte Carlo simulation (RMC). It was noted that the types of short-range order structures are almost the same in the Al60Cu37Fe3 and Al50Cu40Fe10 alloy liquids, while the former has more icosahedral short-range order (ISRO) and the latter has less. The medium-range order (MRO) was characterized by the cluster correlation method and visualization analysis. More obvious structural heterogeneity was found in the Al60Cu37Fe3 liquid, which is due to the strong correlation between clusters with high icosahedral order and the weak correlation between crystal clusters. Moreover, strongly correlated ISRO clusters can form icosahedral medium-range order (IMRO) structures by interpenetrating connections forming a stable structure upon cooling, and some other clusters can even enhance the IMRO stability. Such IMRO will be retained in the liquid upon cooling, leading to QC formation. All the findings provide a further understanding of the liquid-solid transition with ISRO participation.