Class Of Amorphous Materials Research Articles

Accessing versatile tensile ductility of amorphous materials by fractal nanoarchitecture design

Amorphous materials have been known to be intrinsically brittle under tensile stress. This is especially true in silicon-based and metallic-based glasses. In particular, for the latter, they quite often show promising mechanical properties superior to their crystalline counterparts. However, lacking tensile ductility strongly prohibits them from servicing the societies. Although with decades of immense research efforts, we are still waiting for a sophisticated solution. To march in this direction, in this work, we are dedicated to finding a practical method by smart fractal nano-architecture design through advanced computational modeling. This mainly aims to circumvent the intrinsic strain localization at the nano-scale to avoid catastrophic failure. By distributing the external strain to numerous self-confined nano-branches, we successfully achieve astonishing and tunable tensile ductility. This strategy proves to be very effective for different classes of amorphous materials. We found that the tensile properties of the nano-architectured glasses depend on both the constituent elements and the nanostructure. This demonstrates our flexible capability to design desired mechanical properties for a specific material at any spatial length scale. The current findings will inspire experimental realization by cutting-edge 3D-printing techniques and call for optimal design by top-notch graph neural network deep learning algorithms. This work also proposes a new ’structure’-property relationship to efficiently bridge experimental fabrication and computational design.

Metal-Organic Network-Forming Glasses.

The crystal-liquid-glass phase transition of coordination polymers (CPs) and metal-organic frameworks (MOFs) offers attractive opportunities as a new class of amorphous materials. Unlike conventional glasses, coordination chemistry allows the utilization of rational design concepts to fine-tune the desired properties. Although the glassy state has been rare in CPs/MOFs, it exhibits diverse advantages complementary to their crystalline counterparts, including improved mass transport, optical properties, mechanical properties, and the ability to form grain-boundary-free monoliths. This Review discusses the current achievements in improving the understanding of anomalous phase transitions in CPs/MOFs. We elaborate on the criteria for classifying CP/MOF glasses and comprehensively discuss the three common strategies employed to obtain a glassy state. We include all CP/MOF glass research progress since its inception, discuss the current challenges, and express our perspective on future research directions.

Mechanics, Ionics, and Optics of Metal-Organic Framework and Coordination Polymer Glasses.

Melt and glassy states of coordination polymers (CPs)/metal-organic frameworks (MOFs) have gained attention as a new class of amorphous materials. Many bridging ligands such as azolate, nitrile, thiocyanide, thiolate, pyridine, sulfonate, and amide are available to construct crystals with melting temperatures in the range of 60-593 °C. Here, we discuss the mechanism of crystal melting, glass structures, and mechanical properties by considering both experimental and theoretical studies. High and exclusive H+ or Li+ conductivities in moldable CP glasses have been proven in the all-solid-state devices such as fuel cells or secondary batteries. Transparent glasses with wide composition and available dopants are also attractive for nonlinear optics, photoconductivity, emission, and light-harvesting. The ongoing challenge in the field is to develop the design principles of CP/MOF melts and glasses, corresponding functions of mass (ion, electron, photon, phonon, and so forth). transport and conversion, and the integration of devices with the use of their tunable mechanical properties.

Emerging properties of non-crystalline phases of graphene and boron nitride based materials

We review recent developments on the synthesis and properties of two-dimensional materials which, although being mainly of an sp 2 bonding character, exhibit highly disordered, non-uniform and structurally random morphologies. The emergence of such class of amorphous materials, including amorphous graphene and boron nitride, have shown superior properties compared to their crystalline counterparts when used as interfacial films. In this paper we discuss their structural, vibrational and electronic properties and present a perspective of their use for electronic applications.

A New Dimension for Coordination Polymers and Metal-Organic Frameworks: Towards Functional Glasses and Liquids.

There are two categories of coordination polymers (CPs): inorganic CPs (i-CPs) and organic ligand bridged CPs (o-CPs). Based on the successful crystal engineering of CPs, we here propose noncrystalline states and functionalities as a new research direction for CPs. Control over the liquid or glassy states in materials is essential to obtain specific properties and functions. Several studies suggest the feasibility of obtaining liquid/glassy states in o-CPs by design principles. The combination of metal ions and organic bridging ligands, together with the liquid/glass phase transformation, offer the possibility to transform o-CPs into ionic liquids and other ionic soft materials. Synchrotron measurements and computational approaches contribute to elucidating the structures and dynamics of the liquid/glassy states of o-CPs. This offers the opportunity to tune the porosity, conductivity, transparency, and other material properties. The unique energy landscape of liquid/glass o-CPs offers opportunities for properties and functions that are complementary to those of the crystalline state.

Spatial structure of quasilocalized vibrations in nearly jammed amorphous solids

The low-temperature properties of amorphous solids are widely believed to be controlled by low-frequency quasi-localized modes. What governs their spatial structure and density is however debated. We study these questions numerically in very large systems as the jamming transition is approached and the pressure p vanishes. We find that these modes consist of an unstable core in which particles undergo the buckling motions and decrease the energy, and a stable far-field component which increases the energy and prevents the buckling of the core. The size of the core diverges as $p^{-1/4}$ and its characteristic volume as $p^{-1/2}$ These features are precisely those of the anomalous modes known to cause the Boson peak in the vibrational spectrum of weakly-coordinated materials. From this correspondence we deduce that the density of quasi-localized modes must go as $g_{\mathrm{loc}}(\omega) \sim \omega^4/p^2$ , in agreement with previous observations. Our analysis thus unravels the nature of quasi-localized modes in a class of amorphous materials.

Structure and Properties of Nanoglasses

Nanoglasses represent a novel structural modification of amorphous materials, exhibiting properties and structural details that are markedly different from those observed in metallic glasses prepared by rapid quenching. In this review, the synthesis method and the techniques used for charactering the structure of nanoglasses are described together with our current understanding of their salient microstructural features. It is believed that the structure of nanoglasses consists of two distinct amorphous regions give rise to mechanical, thermal, and magnetic properties that are significantly different from those observed in rapidly quenched (RQ) metallic glasses. Nanoglasses, therefore, constitute a distinct new class of amorphous materials and thus opening up new opportunities for their potential use in a number of structural and functional applications.

Multiscale structures and phase transitions in metallic glasses: A scattering perspective**Project supported by Shenzhen Science and Technology Innovation Commission of China (Grant No. R-IND8701) and the Croucher Foundation (Project No. CityU 9500020). Si Lan is partially supported by the Fundamental Research Funds for the Central Universities of China (Grant No. 30915015103) and the National Natural Science Foundation of China (Grant

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.

Melt-cast organic glasses as high-efficiency fast neutron scintillators

In this work we report a new class of organic-based scintillators that combines several of the desirable attributes of existing crystalline, liquid, and plastic organic scintillators. The prepared materials may be isolated in single crystalline form or melt-cast to produce highly transparent glasses that have been shown to provide high light yields of up to 16,000 photons/MeVee, as evaluated against EJ-200 plastic scintillators and solution-grown trans-stilbene crystals. The prepared organic glasses exhibit neutron/gamma pulse-shape discrimination (PSD) and are compatible with wavelength shifters to reduce optical self-absorption effects that are intrinsic to pure materials such as crystalline organics. The combination of high scintillation efficiency, PSD capabilities, and facile scale-up via melt-casting distinguishes this new class of amorphous materials from existing alternatives.

SILICON OXYCARBIDE GLASSES FROM POLYSILOXANES

Silicon oxycarbide glasses (SiOC) are a class of amorphous materials with a similar silica glass structure, in which oxygen atoms are partially replaced by tetracoordenated carbon atoms. The presence of carbon atoms covalently bound to the silicon atoms creates a more interconnected structure with better strength, and excellent chemical stability than conventional silica. SiOCs are easily prepared by the pyrolysis of polysiloxanes and can potentially be implemented in several technological applications that require high temperatures. This paper mainly addresses the preparation, structure, and properties of SiOC. Furthermore, potential applications of SiOC are also introduced.

Equilibrium ultrastable glasses produced by random pinning

Ultrastable glasses have risen to prominence due to their potentially useful material properties and the tantalizing possibility of a general method of preparation via vapor deposition. Despite the importance of this novel class of amorphous materials, numerical studies have been scarce because achieving ultrastability in atomistic simulations is an enormous challenge. Here, we bypass this difficulty and establish that randomly pinning the position of a small fraction of particles inside an equilibrated supercooled liquid generates ultrastable configurations at essentially no numerical cost, while avoiding undesired structural changes due to the preparation protocol. Building on the analogy with vapor-deposited ultrastable glasses, we study the melting kinetics of these configurations following a sudden temperature jump into the liquid phase. In homogeneous geometries, we find that enhanced kinetic stability is accompanied by large scale dynamic heterogeneity, while a competition between homogeneous and heterogeneous melting is observed when a liquid boundary invades the glass at constant velocity. Our work demonstrates the feasibility of large-scale, atomistically resolved, and experimentally relevant simulations of the kinetics of ultrastable glasses.

Relaxation of Bulk Metallic Glasses Studied by Mechanical Spectroscopy

The relaxational dynamics in metallic glasses (MGs) is investigated by using mechanical spectroscopy. The spectra show that in MGs there are two relaxations: (i) the α relaxation, linked to the glass transition, as observed in other classes of amorphous materials; and (ii) the β relaxation, well observed below the glass transition, with an intensity strongly dependent on the MG composition, the nature of which has been linked to the local microstructure of MGs. For the investigated MGs we find that the intensity and relaxation time of the β relaxation depends, in a reproducible fashion, on the thermal history of the samples. During aging experiments, the intensity decreases (as well as the τβ) with a time dependence described well by a stretched exponential, with an exponent β(aging) independent of the driving frequency. Moreover, we find that the activation energy Uβ and the peak temperature Tβp of the β relaxation follow the approximate relationship: Uβ ≈ 31.5RTβp (for driving frequency 1 Hz), indicating that the high temperature limit of the peak frequency is approximately the same for all the MGs investigated. Finally, the frequency separation of the α and β processes in the mechanical loss spectra for La-and Pd-based metallic glasses is tested against the prediction of the Coupling Model.

Thermodynamics and fragility of glass-forming alloys

Abstract The existing correlation between the extensive properties, Δ H and Δ S , the enthalpy and entropy difference between liquid and crystal phases has been checked to relate metallic glasses to other classes of amorphous materials. Expressing the specific heat difference, Δ C p , of molten and crystalline metallic glass-formers as a function of temperature with different functional trends, parametric expressions of fragility are derived using relevant temperatures for alloys. It is shown that relationships between the Δ S g /Δ C p,g ratio and such temperatures are useful to estimate unknown quantities when the experimental determination of the specific heat is possible. Thermodynamic indicators of fragility are compared to the kinetic fragility obtained from viscosity data accounting for the estimated errors on parameters which are derived from extrapolations. The outcome of the analysis indicates that a relationship between thermodynamic and kinetic parameters exists. Moreover a systematic scatter for some alloys indicates a diverse behavior which can be ascribed to structure modification either in the liquid or in the solid reference state.

Structural Models of Selenite Glasses Containing Ag<sup>+</sup> and Cu<sup>2+</sup> Ions

Selenite glasses are a new class of amorphous materials which are interesting mainly from a scientific point of view and they are not yet fully examined. Selenite glasses containing other non-traditional glass formers (TeO2, V2O5 and MoO3) as well as network modifiers (Ag+, Cu2+, Zn2+, etc.) were obtained. The aim of the present study is to explain the glass formation ability in selenite systems with the participation of modifiers (Ag+ and Cu2+) and MoO3.

Pressure-Induced Structural Transformation in Radiation-Amorphized Zircon

We study the response of a radiation-amorphized material to high pressure. We have used zircon ZrSiO4 amorphized by natural radiation over geologic times, and have measured its volume under high pressure, using the precise strain-gauge technique. On pressure increase, we observe apparent softening of the material, starting from 4 GPa. Using molecular dynamics simulation, we associate this softening with the amorphous-amorphous transformation accompanied by the increase of local coordination numbers. We observe permanent densification of the quenched sample and a nontrivial "pressure window" at high temperature. These features point to a new class of amorphous materials that show a response to pressure which is distinctly different from that of crystals.

Conductivity of maltose–water–KCl mixtures in the supercooled liquid and glassy states

The conductivities of low water content amorphous maltose–water–KCl mixtures have been measured using both direct current and alternating current techniques at temperatures ranging from –60 °C to 85 °C. The mixtures all contained 11.6% w/w water and between 0.0052% w/w and 0.52% w/w KCl which resulted in mixtures with a calorimetric glass-transition temperature, Tg, of –5 °C. In the supercooled region, as the temperature is reduced to Tg, the activation energy of the conductivity increases from 80–85 kJ mol–1 to 155–165 kJ mol–1 and the conductivity is found to depend upon the viscosity to the power –0.52, which indicate that the conductivity is uncoupled from the viscosity. In the glassy region, as the temperature is reduced below Tg, the conductivity falls at a reduced rate with an activation energy of 60–75 kJ mol–1, a value which is similar to the activation energy of the secondary dielectric relaxation process in the glass. Qualitatively similar conductivity behaviour has been observed in other classes of amorphous materials, such as polymers and ionic glasses. The ability of conduction measurements to probe translational mobility in supercooled and glassy states makes it suitable for investigating the effects of molecular structure and size on mobility.

Holographic time-of-flight measurements of the hole-drift mobility in a photorefractive polymer.

The holographic time-of-flight (HTOF) technique is applied in a photorefractive polymer. The electric-field, temperature, and drift-length dependencies of the hole-drift mobility are shown to be consistent with previously published data. It is suggested that the shape of the HTOF signal reflects the degree of charge-transport disorder in this class of amorphous materials.

Atomic disorder produced in cobalt aluminide by mechanical milling

This chapter focuses on amorphous magnetic rare earth alloys. These metal-metalloid amorphous alloys are produced typically by either rapid quenching from the liquid state, electro-deposition from solution, electro-less deposition, or evaporation onto cooled substrates. In late 1972, a new class of amorphous materials was produced: the rare earth-transition metal amorphous alloys (e.g. Tb0.33 Fe0.66 or simply TbFe2) that contained no metalloid or glass-former atoms. The rare earth amorphous alloys were found to possess a number of unique features, mostly related to their magnetic state, including magnetic bubble domain propagation, a giant coercive field behavior at low temperatures, evidence of angstrom-sized magnetic micro-domains, and a unique dependence of bulk magnetic ordering temperatures (Curie points) on magnitude of the rare earth effective spin. This chapter discusses these and other aspects of the rare earth transition metal amorphous materials.

Production of nanocrystals by high energy ball milling

This chapter focuses on amorphous magnetic rare earth alloys. These metal-metalloid amorphous alloys are produced typically by either rapid quenching from the liquid state, electro-deposition from solution, electro-less deposition, or evaporation onto cooled substrates. In late 1972, a new class of amorphous materials was produced: the rare earth-transition metal amorphous alloys (e.g. Tb0.33 Fe0.66 or simply TbFe2) that contained no metalloid or glass-former atoms. The rare earth amorphous alloys were found to possess a number of unique features, mostly related to their magnetic state, including magnetic bubble domain propagation, a giant coercive field behavior at low temperatures, evidence of angstrom-sized magnetic micro-domains, and a unique dependence of bulk magnetic ordering temperatures (Curie points) on magnitude of the rare earth effective spin. This chapter discusses these and other aspects of the rare earth transition metal amorphous materials.

Ion-Beam-Induced Amorphization of Complex Ceramic Materials—Minerals

As early as 1893, mineralogist W.C. Broegger recognized the first example of the transition from the crystalline to aperiodic (amorphous) state in minerals and defined the term “metamikte.” Metamict minerals were considered to be one of three classes of amorphous materials (porodine and hyaline being the other two), but distinguishable as phases that were originally crystalline, as evidenced by well-developed crystal faces. The amorphous state was determined on the basis of a characteristic conchoidal fracture and optical isotropy. There was no mention of radiation damage as a potential cause. In 1914, Hamberg first suggested that metamictization is a radiation-induced, periodic-to-aperiodic phase transition caused by alpha-decay of the constituent radioactive uranium and thorium. In the late 1930s, Stackelberg and Rottenbach tried to test this hypothesis directly by bombarding a thin slab of zircon with alpha particles. Although unsuccessful, the experiment must have been one of the first in which an “ion beam” was used to “modify” a material. After this early effort, there was little research on metamict minerals, and they remained a mineralogical curiosity.R.C. Ewing's interest in this topic began in the early 1970s. Since then, there has been a continuing research program using modern analytical techniques on minerals that have received α-decay doses up to 1026α-decay events/m3over geologic time periods up to 109years. As an example, electron diffraction patterns have shown that naturally occurring zirconolites (CaZrTi2O7) containing varying concentrations of thorium oxide (up to 19 wt% ThO2) are amorphized to different degrees depending on their age and the resulting α-decay event dose (Figure 1).