Glasses are monolithic materials and their extended structure ranges from the physics and chemistry played out on the atomic scale and nanoscale to the engineering dimensions of cast products. Very few defects are generated during glass solidification, apart from microcracks at the surface, making glassy materials and their extended structures uniquely different from crystalline materials. This account draws together experimental techniques that probe on many length scales the structures of insulating network glasses, as well as those of metallic glasses. The extended structure has common elements for nonconducting as well as conducting glasses. It ranges from average static atomic nearest-neighbor arrangements, correlations between free volume voids, to many-atom structural dynamics and density fluctuations. The latter are signatures of the non-ergodicity of the supercooled state captured close to the glass transition. As individual experimental techniques necessarily underdetermine glass structure, computational modeling is essential to assemble three-dimensional structures that agree with different independent experiments. This is particularly important in studying complex glasses that are invariably not homogeneous, even on the atomic scale. Indeed, clarifying this heterogeneity helps to throw light on the different applications of glasses. In bringing together observation and modeling of glass structures, the main aim of this chapter is to visualize their extended nature, starting on the scale of atoms and molecules, in order to try and understand functionality on the macroscale.

Well-defined density functional theory (DFT) calculations are performed as the first exploratory study for the atomic and electronic mechanism of defect mediated morphology and optical propertiesof CdnSen (n=3, 10, 13, and 33) quantum dots (QDs) in inorganic amorphous matrix. The intrinsic defects of pristine CdSe QDs, and the interfacial defects between the QDs and surrounding amorphous matrix, were systematically studied. The calculated electronic structure suggested that the pristine CdSe QDs capped by the structural modifiers or non-bridging oxygen in the amorphous matrix gave rise to the structure reconstruction and paired defect states at the edge of the valence and conduction bands. The orbital analysis elucidated that the redistribution of the majority of HOMO and LUMO electron density was localized over the bonds formed by capping atoms and QDs. These changes in the electronic structures were further demonstrated by CdSe QDs embedded sodium silicate glasses. It turned out that Se atoms at QDs/glass interface were much more active than those found on the surface of organically passivated CdSe QDs. The results serve as a new paradigm in materials research to explore structural origins of defect emission from QDs and a new strategy to develop glasses containing QDs with high photoluminescence quantum efficiency.

In the version of this Review Article originally published, parentheses were misplaced and the longitudinal and transverse speeds were inverted in two expressions for Poisson’s ratio in Box 2; the expressions should have read, respectively, ν = (3 B / G – 2)/(6 B / G + 2) and ν = [½( V l / V t ) 2 − 1]/[( V l / V t ) 2 − 1].

Despite forming the critical basis for technologies in separation, catalysis, nuclear waste containment and biomedical applications, the relationship between the structural topology of the microporous framework materials and energetics of their formation and stability remain poorly understood.In this study, microporous materials including ZIF-8 and inorganic zeolites are being investigated using molecular dynamics methods and density functional theory (DFT) to reveal the structural changes and possible phase transitions in these structures at high pressure.In order to detect if phase transitions occur, the changes in the volume of the simulation cell are recorded with increasing pressure.In addition, the reversibility of the transition are followed by de-pressurizing compressed structures.Molecular dynamics snapshots at different stages in compression and decompression are used to identify pressure-induced phase transitions, including pressure-induced amorphization, and their decompression to the crystalline starting point.The diffraction patterns, radial distribution functions, and vibrational density of states calculated from the simulations are compared with experimental data.DFT simulations of ZIF-8 at high pressure, for example, have provided insight into changes associated with pressure-induced amorphization involving a low density amorphous (LDA) phase and a high density amorphous (HDA) phase.

We have theoretically investigated the elastic properties of three topologically identical zeolitic imidazolate frameworks: ZIF-4, ZIF-62 and TIF-4, by means of ab initio calculations. The ZIFs are a subset of metal organic frameworks (MOFs), whose versatile functionality is providing exciting opportunities in solid state science. Understanding the relationship between structure and elastic properties of hybrid materials is making it possible to develop a new generation of functional materials. In this work we have determined the bulk (K), shear (G) and Young's moduli (E), together with Poisson's ratio(υ), and the universal elastic anisotropy index (A^U) from the computed elastic coefficients. Tensorial analysis of the elastic constants reveals unusual and highly anisotropic elastic behaviour. All three materials exhibit low Young's and shear moduli. In addition, their flexibility incorporates regions of negative Poisson's ratio (NPR) and negative linear compressibility (NLC). The elastic properties of these ZIF crystals are are affected by the substituted organic linkages.

Crystalline solids dominate the field of metal-organic frameworks (MOFs), with access to the liquid and glass states of matter usually prohibited by relatively low temperatures of thermal decomposition. In this work, we give due consideration to framework chemistry and topology to expand the phenomenon of the melting of 3D MOFs, linking crystal chemistry to framework melting temperature and kinetic fragility of the glass-forming liquids. Here we show that melting temperatures can be lowered by altering the chemistry of the crystalline MOF state, which provides a route to facilitate the melting of other MOFs. The glasses formed upon vitrification are chemically and structurally distinct from the three other existing categories of melt-quenched glasses (inorganic nonmetallic, organic, and metallic), and retain the basic metal-ligand connectivity of crystalline MOFs, which connects their mechanical properties to their starting chemical composition. The transfer of functionality from crystal to glass points toward new routes to tunable, functional hybrid glasses.

Periodic and molecular cluster models are presented for anorthite (CaAl2Si2O8), a cement forming glass with desirable thermal and mechanical properties also tested in dental applications. Both the crystalline and amorphous structures were characterised by ab initio molecular dynamics and found to be in good agreement with experiment. Additional investigations of the elongation and fracture of the glass were also made. The recovery of material properties signaled the failure of the periodic method to generate acceptable fracture surfaces to model cement forming-sites. Isolated molecular cluster models of anorthite were therefore investigated with electronic structure methods and showed sound structural matches with the traditional periodic structures. The equilibrated glass clusters were used to develop cement models, through binding of short acid oligomers to selected Al-centres, simulating the glass-polymer interface. Overall, the anorthite glass structures emerging from periodic and cluster models were in close agreement. Results suggest that bare molecular cluster models represent an alternative avenue for accurately investigating amorphous systems, providing more realistic descriptions of edge and corner sites, as well as interfaces.

The nanostructured Ce ion substituted cryptomelane-type octahedral molecular sieve (OMS-2) catalyst exhibits strong absorption in the entire solar spectrum region. The Ce ion substituted OMS-2 catalyst can efficiently transform the absorbed solar energy to thermal energy, resulting in a considerable increase of temperature. By combining the efficient photothermal conversion and thermocatalytic activity of the Ce ion substituted OMS-2 catalyst, we carried out full solar spectrum, visible-infrared, and infrared light driven catalysis with extremely high efficiency. Under the irradiation of full solar spectrum, visible-infrared, and infrared light, the Ce ion substituted OMS-2 catalyst exhibits extremely high catalytic activity and excellent durability for the oxidation of volatile organic pollutants such as benzene, toluene, and acetone. Based on the experimental evidence, we propose a novel mechanism of solar light driven thermocatalysis for the Ce ion substituted OMS-2 catalyst. The reason why the Ce ion substituted OMS-2 catalyst exhibits much higher catalytic activity than pure OMS-2 and CeO2/OMS-2 nano composite under the full solar spectrum irradiation is discussed.

The G338 ionomer glass is a fluoro-alumino-silicate system, which is used as the powder component of glass ionomer cements (GICs) in dental applications. However, despite progress in understanding the nature of this glass, chemical identity of its separated amorphous phases has not yet been conclusively determined. In this work, we identify these phases by performing differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses on both the as-received glass and heat-treated samples. We detected three glass transitions in the as-received G338 glass during DSC upscanning, implying the co-existence of three amorphous phases. Towards resolving the chemical identity of the three phases, we performed XRD analyses on samples subjected to dynamic heating, while further DSC and XRD analyses were performed on samples subjected to isothermal treatment. The results suggest that the three amorphous phases in G388 are Ca/Na–Al–Si–O, Ca–Al–F and Ca–P–O–F phases, respectively. However, the exact chemical compositions of the three phases still require further exploration. The results of this work are important for understanding the impact of phase separation within ionomer glasses on the setting behavior of GICs, and hence improving performances of GICs by optimizing the glass production conditions.

We report on a compact laser-heated aerodynamic levitation facility which can be used for studies of thermophysical properties like density, surface tension and viscosity of liquid oxides at high temperatures. The facility is characterized by employing an acoustic excitation system for controlled excitation of droplet oscillations which is key for measurements of surface tension and viscosity. Results of measurements of density and viscosity of pure liquid Al 2 O 3 as well as CaAl 2 O 4 are presented. The data are discussed in the context of available literature data. It is shown that with the present setup the experimentally accessible temperature ranges could be enlarged. For viscosity high precision data for high melting point and highly reactive oxide melts can now be obtained using aerodynamic levitation.

We have investigated the effects of helium ion irradiation energy and sample temperature on the performance of grain boundaries as helium sinks in ultrafine grained and nanocrystalline tungsten. Irradiations were performed at displacement and non-displacement energies and at temperatures above and below that required for vacancy migration. Microstructural investigations were performed using Transmission Electron Microscopy (TEM) combined with either in-situ or ex-situ ion irradiation. Under helium irradiation at an energy which does not cause atomic displacements in tungsten (70 eV), regardless of temperature and thus vacancy migration conditions, bubbles were uniformly distributed with no preferential bubble formation on grain boundaries. At energies that can cause displacements, bubbles were observed to be preferentially formed on the grain boundaries only at high temperatures where vacancy migration occurs. Under these conditions, the decoration of grain boundaries with large facetted bubbles occurred on nanocrystalline grains with dimensions less than 60 nm. We discuss the importance of vacancy supply and the formation and migration of radiation-induced defects on the performance of grain boundaries as helium sinks and the resulting irradiation tolerance of ultrafine grained and nanocrystalline tungsten to bubble formation.

We examine the route of structural collapse and re-crystallization of faujasite-type (Na,K)-LSX zeolite. As the first step, a rather stable amorphous high density phase HDAcollapse is generated through an order-disorder transition from the original zeolite via a low density phase LDAcollapse, at around 790 °C. We find that the overall amorphization is driven by an increase in the bond angle distribution within T-O-T and a change in ring statistics to 6-membered TO4 (T = Si(4+), Al(3+)) rings at the expense of 4-membered rings. The HDAamorph transforms into crystalline nepheline, though, through an intermediate metastable carnegieite phase. In comparison, the melt-derived glass of similar composition, HDAMQ, crystallizes directly into the nepheline phase without the occurrence of intermediate carnegieite. This is attributed to the higher structural order of the faujasite-derived HDAcollapse which prefers the re-crystallization into the highly symmetric carnegieite phase before transformation into nepheline with lower symmetry.

The effect of helium implantation fluences in French nuclear borosilicate glass on He bubble nucleation and growth mechanisms was characterised using in-situ TEM experiments. Observations of implanted glass at 143K indicate that a helium concentration of around 3 at.% is required to nucleate a significant density of nanosized bubbles. He bubble growth is observed for He concentration higher than the estimated number of helium host (> 4 at.%). These results highlight the large capacity of the glassy network for incorporating helium atoms.

Using experiments and computer simulations, we find that 80keV Xe ion irradiation of Au nanorods can produce sputtering yields exceeding 1000, which to our knowledge are the highest yields reported for sputtering by single ions in the nuclear collision regime. This value is enhanced by more than an order of magnitude compared to the same irradiation of flat Au surfaces. Using MD simulations, we show that the very high yield can be understood as a combination of enhanced yields due to low incoming angles at the sides of the nanowire, as well as the high surface-to-volume ratio causing enhanced explosive sputtering from heat spikes. We also find, both in experiments and simulations, that channeling has a strong effect on the sputtering yield: if the incoming beam happens to be aligned with a crystal axis of the nanorod, the yield can decrease to about 100.

This article explores Poisson's ratio, starting with the controversy concerning its magnitude and uniqueness in the context of the molecular and continuum hypotheses competing in the development of elasticity theory in the nineteenth century, moving on to its place in the development of materials science and engineering in the twentieth century, and concluding with its recent re-emergence as a universal metric for the mechanical performance of materials on any length scale. During these episodes France lost its scientific pre-eminence as paradigms switched from mathematical to observational, and accurate experiments became the prerequisite for scientific advance. The emergence of the engineering of metals followed, and subsequently the invention of composites-both somewhat separated from the discovery of quantum mechanics and crystallography, and illustrating the bifurcation of technology and science. Nowadays disciplines are reconnecting in the face of new scientific demands. During the past two centuries, though, the shape versus volume concept embedded in Poisson's ratio has remained invariant, but its application has exploded from its origins in describing the elastic response of solids and liquids, into areas such as materials with negative Poisson's ratio, brittleness, glass formation, and a re-evaluation of traditional materials. Moreover, the two contentious hypotheses have been reconciled in their complementarity within the hierarchical structure of materials and through computational modelling.

The development of novel contactless aerodynamic laser heated levitation techniques is reported that enable thermophysical properties of refractory liquids to be measured in situ in the solid, liquid, and supercooled liquid state and demonstrated here for alumina. Starting with polished crystalline ruby spheres, we show how, by accurately measuring the changing radius, the known density in the solid state can be reproduced from room temperature to the melting point at 2323 K. Once molten, by coupling the floating liquid drop to acoustic oscillations via the levitating gas, the mechanical resonance and damping of the liquid can be measured precisely with high-speed high-resolution shadow cast imaging. The resonance frequency relates to the surface tension, the decay constant to the viscosity, and the ellipsoidal size and shape of the levitating drop to the density. This unique instrumentation enables these related thermophysical properties to be recorded in situ over the entire liquid and supercooled range of alumina, from the boiling point at 3240 K, until spontaneous crystallization occurs around 1860 K, almost 500 below the melting point. We believe that the utility that this unique instrumentation provides will be applicable to studying these important properties in many other high temperature liquids.

Graphitic materials and graphite composites experience dimensional change when exposed to radiation-induced atomic displacements. This has major implications for current and future technological ranging from nuclear fission reactors to the processing of graphene-silicon hybrid devices. Dimensional change in nuclear graphites is a complex problem involving the filler, binder, porosity, cracks and atomic-level effects all interacting within the polygranular structure. An improved understanding of the atomistic mechanisms which drive dimensional change within individual graphitic crystals is required to feed into the multiscale modelling of this system.In this study, micromechanically exfoliated samples of highly oriented pyrolytic graphite have been ion irradiated and studied in situ using transmission electron microscopy (TEM) in order to gain insights into the response of single graphitic crystals to displacing radiation. Under continuous ion bombardment, a complex dynamic sequence of deformation evolves featuring several distinct stages from the inducement of strain, the creation of dislocations leading to dislocation arrays, the formation of kink band networks and localised doming of the sample. Observing these ion irradiation-induced processes using in situ TEM reveals previously unknown details of the sequence of microstructural developments and physics driving these phenomena. A mechanistic model consistent with the microstructural changes observed is presented. (C) 2013 Elsevier Ltd. All rights reserved.

Aerodynamic levitation is an effective way to suspend samples which can be heated with CO2 lasers. The advantages of this containerless technique are the simplicity and compactness of the device, making it possible to integrate it easily in different kinds of experiments. In addition, all types of materials can be used, including metals and oxides. The integration of aerodynamic levitation at synchrotron and neutron sources provides powerful tools to study the structure and dynamics of molten materials. We present here an overview of the existing techniques and of the developments made at the CEMHTI in Orléans, as well as a few examples of experimental results already obtained.