Discovery of Ultra-Crack-Resistant Oxide Glasses with Adaptive Networks
TL;DR: In this article, a melt-quenched lithium aluminoborate glass featuring the highest crack resistance for a bulk oxide glass is reported, which is based on combined mechanical and structural characterizations.
Abstract: Despite their transformative role in our society, oxide glasses remain brittle. Although extrinsic postprocessing techniques can partially mitigate this drawback, they come with undesirable side effects. Alternatively, topological engineering offers an attractive option to enhance the intrinsic strength and damage resistance of glass. On the basis of this approach, we report here the discovery of a novel melt-quenched lithium aluminoborate glass featuring the highest crack resistance ever reported for a bulk oxide glass. Relying on combined mechanical and structural characterizations, we demonstrate that this unusual damage resistance originates from a significant self-adaptivity of the local atomic topology under stress, which, based on a selection of various oxide glasses, is shown to control crack resistance. This renders the lithium aluminoborate glass a promising candidate for engineering applications, such as ultrathin, yet ultrastrong, protective screens.
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TL;DR: In this article, Raman microspectroscopy was used to characterize amorphous silica plastic behavior and a map of the local residual indentation-induced densification was obtained.
Abstract: Raman microspectroscopy was used to characterize amorphous silica plastic behavior. Using a correlation between Raman spectrum and density, a map of the local residual indentation-induced densification is obtained. The existence of a densification-induced hardening is also evidenced through a diamond anvil cell experiment. Such observations are not accounted for by the previously proposed hardening-free pressure-dependent yield criterion based on indentation curves. These results open the way to more accurate description of a constitutive law for amorphous silica.
108 citations
TL;DR: This approach combines molecular dynamics simulations with topological constraint theory with a simple, yet powerful framework that can be used to predict the compositional dependence of glass properties or pinpoint promising compositions with tailored functionalities.
70 citations
01 Mar 2019
TL;DR: In this article, the authors reviewed the experimental work on identification and quantification of indentation deformation in glasses, as well as probing the accompanying structural changes in the glassy network.
Abstract: Improving the fracture resistance of oxide glasses through adjustment of the chemical composition remains a challenging task, although composition-mechanical property relations have been established for simple model systems. The glass mechanical properties are, among other methods, conventionally tested using instrumented indentation, which is a fast and convenient technique that mimics the real-life damage for certain applications, although interpretation can be challenging due to the complex stress fields that develop under the indenter. Early indentation experiments have shown that oxide glasses exhibit pronounced tendency to densify under compressive load compared to metals and ceramics. After decades of investigations, it is now known that the extent of densification is strongly dependent on the glass' chemical composition and in turn its atomic packing density and Poisson's ratio. Spectroscopic techniques have shed light on the mechanism of densification, which include changes in the bond angle distributions as well as an increase in the coordination number of the network-forming cations. Knowledge of such details is crucial for understanding the link between chemical composition and resistance to cracking in oxide glasses, since densification is an efficient way to dissipate the elastic energy applied to the material during indentation. Here, we review the experimental work on identification and quantification of indentation deformation in glasses, as well as on probing the accompanying structural changes in the glassy network. We also include the conclusions drawn from computer simulation studies, which can provide atomistic details of the indentation deformation mechanisms. Finally, we discuss the link between the mechanism of deformation and the crack resistance.
70 citations
TL;DR: From direct observation of deformation‐induced variations on the characteristic length‐scale of molecular heterogeneity, it is revealed that rigidity fluctuation mediates the deformation process of inorganic glasses.
Abstract: Microscopic deformation processes determine defect formation on glass surfaces and, thus, the material's resistance to mechanical failure. While the macroscopic strength of most glasses is not directly dependent on material composition, local deformation and flaw initiation are strongly affected by chemistry and atomic arrangement. Aside from empirical insight, however, the structural origin of the fundamental deformation modes remains largely unknown. Experimental methods that probe parameters on short or intermediate length-scale such as atom-atom or superstructural correlations are typically applied in the absence of alternatives. Drawing on recent experimental advances, spatially resolved Raman spectroscopy is now used in the THz-gap for mapping local changes in the low-frequency vibrational density of states. From direct observation of deformation-induced variations on the characteristic length-scale of molecular heterogeneity, it is revealed that rigidity fluctuation mediates the deformation process of inorganic glasses. Molecular field approximations, which are based solely on the observation of short-range (interatomic) interactions, fail in the prediction of mechanical behavior. Instead, glasses appear to respond to local mechanical contact in a way that is similar to that of granular media with high intergranular cohesion.
49 citations
TL;DR: A fracture pattern of a MOF glass upon indentation is obtained, and anomalous cracking behavior is revealed, which is attributed to the easy breakage of the coordinative bonds (Zn−N) in ZIF glasses, since these bonds are much weaker than the ionic and covalent bonds in network glasses.
Abstract: Metal-organic framework (MOF) glasses are a newly emerged family of melt-quenched glasses. Recently, several intriguing features, such as ultrahigh glass-forming ability and low liquid fragility, have been discovered in a number of zeolitic imidazolate frameworks (ZIFs) that are a subset of MOFs. However, the fracture behavior of ZIF glasses has not been explored. Here we report an observation of both cracking pattern and shear bands induced by indentation in a representative melt-quenched ZIF glass, that is, ZIF-62 glass (ZnIm1.68bIm0.32). The shear banding in the ZIF glass is in strong contrast to the cracking behavior of other types of fully polymerized glasses, which do not exhibit any shear bands under indentation. We attribute this anomalous cracking behavior to the easy breakage of the coordinative bonds (Zn-N) in ZIF glasses, since these bonds are much weaker than the ionic and covalent bonds in network glasses.
40 citations
Cites background from "Discovery of Ultra-Crack-Resistant ..."
...In previous studies, the indentation modulus of ZIF-62 glass was determined to be about 6 GPa, by means of nanoindentation (8), while its Poisson’s ratio was found, by Brillouin scattering, to be 0.45 (10)....
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...65 GPa, and it is thus much softer than inorganic network glasses, for example, oxide glasses that possess a range of hardness of 3 GPa to 9 GPa (36)....
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...1B, the hardness first decreases drastically from 0.65 GPa to 0.53 GPa with increasing load from 0.1 N to 0.2 N, and then gradually decreases from 0.53 GPa to 0.50 GPa for higher indentation loads....
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...1, the hardness of bulk ZIF-62 glass lies in the range of 0.5 GPa to 0.65 GPa, and it is thus much softer than inorganic network glasses, for example, oxide glasses that possess a range of hardness of 3 GPa to 9 GPa (36)....
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TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
51,997 citations
TL;DR: In this paper, the authors used a Berkovich indenter to determine hardness and elastic modulus from indentation load-displacement data, and showed that the curve of the curve is not linear, even in the initial stages of the unloading process.
Abstract: The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
22,557 citations
TL;DR: In this article, the authors investigated the effect of surface scratches on the mechanical strength of solids, and some general conclusions were reached which appear to have a direct bearing on the problem of rupture, from an engineering standpoint, and also on the larger question of the nature of intermolecular cohesion.
Abstract: In the course of an investigation of the effect of surface scratches on the mechanical strength of solids, some general conclusions were reached which appear to have a direct bearing on the problem of rupture, from an engineering standpoint, and also on the larger question of the nature of intermolecular cohesion. The original object of the work, which was carried out at the Royal Aircraft Establishment, was the discovery of the effect of surface treatment—such as, for instance, filing, grinding or polishing—on the strength of metallic machine parts subjected to alternating or repeated loads. In the case of steel, and some other metals in common use, the results of fatigue tests indicated that the range of alternating stress which could be permanently sustained by the material was smaller than the range within which it was sensibly elastic, after being subjected to a great number of reversals. Hence it was inferred that the safe range of loading of a part, having a scratched or grooved surface of a given type, should be capable of estimation with the help of one of the two hypotheses of rupture commonly used for solids which are elastic to fracture. According to these hypotheses rupture may be expected if (a) the maximum tensile stress, ( b ) the maximum extension, exceeds a certain critical value. Moreover, as the behaviour of the materials under consideration, within the safe range of alternating stress, shows very little departure from Hooke’s law, it was thought that the necessary stress and strain calculations could be performed by means of the mathematical theory of elasticity.
10,162 citations
TL;DR: The most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows, are described and some relevant procedures of the software are carried out.
Abstract: In this work we briefly describe the most relevant features of WSXM, a freeware scanning probe microscopy software based on MS-Windows. The article is structured in three different sections: The introduction is a perspective on the importance of software on scanning probe microscopy. The second section is devoted to describe the general structure of the application; in this section the capabilities of WSXM to read third party files are stressed. Finally, a detailed discussion of some relevant procedures of the software is carried out.
6,996 citations
TL;DR: The onset of a sharp change in ddT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature.
Abstract: Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in d dT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature T(K), and the fragility of the liquid, may thus be connected.
4,016 citations