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Metal-organic framework glasses are gaining interest, but large samples are difficult to fabricate and mechanical properties are not well understood. Here, the authors use experiments and simulations to assess fracture toughness and flexural strength of a zeolitic imidazolate framework glass.

Poisson’s ratio (ν) defines a material’s propensity to laterally expand upon compression, or laterally shrink upon tension for non-auxetic materials. This fundamental metric has traditionally, in some fields, been assumed to be a material-independent constant, but it is clear that it varies with composition across glasses, ceramics, metals, and polymers. The intrinsically elastic metric has also been suggested to control a range of properties, even beyond the linear-elastic regime. Notably, metallic glasses show a striking brittle-to-ductile (BTD) transition for ν-values above ~0.32. The BTD transition has also been suggested to be valid for oxide glasses, but, unfortunately, direct prediction of Poisson’s ratio from chemical composition remains challenging. With the long-term goal to discover such high-ν oxide glasses, we here revisit whether previously proposed relationships between Poisson’s ratio and liquid fragility (m) and atomic packing density (Cg) hold for oxide glasses, since this would enable m and Cg to be used as surrogates for ν. To do so, we have performed an extensive literature review and synthesized new oxide glasses within the zinc borate and aluminoborate families that are found to exhibit high Poisson’s ratio values up to ~0.34. We are not able to unequivocally confirm the universality of the Novikov-Sokolov correlation between ν and m and that between ν and Cg for oxide glass-formers, nor for the organic, ionic, chalcogenide, halogenide, or metallic glasses. Despite significant scatter, we do, however, observe an overall increase in ν with increasing m and Cg, but it is clear that additional structural details besides m or Cg are needed to predict and understand the composition dependence of Poisson’s ratio. Finally, we also infer from literature data that, in addition to high ν, high Young’s modulus is also needed to obtain glasses with high fracture toughness.

Abstract Background Financial risk protection is a core dimension of universal health coverage. Hardship financing, defined as borrowing and selling land or assets to pay for healthcare, is a measure of last recourse. Increasing indebtedness and high interest rates, particularly among unregulated money lenders, can lead to a vicious cycle of poverty and exacerbate inequity. Methods To inform efforts to improve Cambodia’s social health protection system we analyze 2019–2020 Cambodia Socio-economic Survey data to assess hardship financing, illness and injury related productivity loss, and estimate related economic impacts. We apply two-stage Instrumental Variable multiple regression to address endogeneity relating to net income. In addition, we calculate a direct economic measure to facilitate the regular monitoring and reporting on the devastating burden of excessive out-of-pocket expenditure for policy makers. Results More than 98,500 households or 2.7% of the total population resorted to hardship financing over the past year. Factors significantly increasing risk are higher out-of-pocket healthcare expenditures, illness or injury related productivity loss, and spending of savings. The economic burden from annual lost productivity from illness or injury amounts to US$ 459.9 million or 1.7% of GDP. The estimated household economic cost related to hardship financing is US$ 250.8 million or 0.9% of GDP. Conclusions Such losses can be mitigated with policy measures such as linking a catastrophic health coverage mechanism to the Health Equity Funds, capping interest rates on health-related loans, and using loan guarantees to incentivize microfinance institutions and banks to refinance health-related, high-interest loans from money lenders. These measures could strengthen social health protection by enhancing financial risk protection, mitigating vulnerability to the devastating economic effects of health shocks, and reducing inequities.

The apparent relationship between Poisson's ratio and fracture energy has been used to guide the discovery of ductile glasses with a brittle-to-ductile (BTD) transition at Poisson's ratio around 0.32. Most organic and metallic glasses possess Poisson's ratio above 0.32, and thus, feature fracture energy that is around three orders of magnitude higher than that of oxide glasses, which feature Poisson's ratio typically below 0.30. However, whether the BTD transition can also be observed in oxide glasses remains unknown due to the lack of fracture energy measurements on oxide glasses with high Poisson's ratio. In this work, we measure the fracture energy of six oxide glasses with high Poisson's ratio between 0.30 and 0.34. We find no clear relationship between the two parameters even in those that possess the same Poisson's ratio as ductile metallic glasses. This suggests that Poisson's ratio is not the main property to enhance the fracture energy of oxide glasses. To this end, we instead find a positive relation between fracture energy and Young's modulus of oxide glasses, and even for some metallic glasses, which could explain their absence of ductility. [ABSTRACT FROM AUTHOR]

Deciphering the structure–property relations of densified oxide glasses is a problem of longstanding interest. For example, it is important for understanding the fracture mechanism under sharp contact loading as well as fabricating glasses with tunable physical characteristics. Recent advances in both experimental and simulation techniques have prompted research breakthroughs in understanding the response of glasses to high pressure. In this Perspective, we first briefly discuss the facilities for the high-pressure treatment of glasses, including in situ and ex situ investigations. The recent work on pressure-induced structural changes of archetypical oxide glass families (silicates, germanates, borates, aluminates, phosphates) is discussed and compared to the changes in macroscopic properties induced by densification, as densification treatment can be used to produce oxide glasses with improved hardness, stiffness, and toughness. We also discuss the new insights from atomistic simulations combined with topological analysis tools to unravel the densification mechanism of oxide glasses on the medium-range order length scale. Drawing on these recent studies, we clarify how densification treatment has proved to be an important tool to both understand the disordered nature of glasses and tune their physical properties, although many open questions and challenges remain that require further investigations. [ABSTRACT FROM AUTHOR]

Deciphering the structure-property relations of densified oxide glasses is a problem of longstanding interest. For example, it is important for understanding the fracture mechanism under sharp contact loading as well as fabricating glasses with tunable physical characteristics. Recent advances in both experimental and simulation techniques have prompted research breakthroughs in understanding the response of glasses to high pressure. In this Perspective, we first briefly discuss the facilities for the high-pressure treatment of glasses, including in situ and ex situ investigations. The recent work on pressure-induced structural changes of archetypical oxide glass families (silicates, germanates, borates, aluminates, phosphates) is discussed and compared to the changes in macroscopic properties induced by densification, as densification treatment can be used to produce oxide glasses with improved hardness, stiffness, and toughness. We also discuss the new insights from atomistic simulations combined with topological analysis tools to unravel the densification mechanism of oxide glasses on the medium-range order length scale. Drawing on these recent studies, we clarify how densification treatment has proved to be an important tool to both understand the disordered nature of glasses and tune their physical properties, although many open questions and challenges remain that require further investigations. [ABSTRACT FROM AUTHOR]

In this work, we study the structure–topology–property relations of a series of melt‐quenched lithium germanate glasses. These glasses exhibit the so‐called germanate anomaly, that is, the germanium atoms feature a distribution of four‐coordinated and higher coordinated germanium species, manifesting itself as anomalies in several material properties. Here, we couple variations in the number of atomic bond constraints with measured variations in thermal and mechanical properties, including thermal conductivity, Vickers hardness, and fracture toughness. For thermal conductivity, a strong correlation is found with sound velocity as well as with the volumetric constraint density. For hardness, a good correlation with volumetric constraint density is found, whereas, for fracture toughness, variations in network topology alone are insufficient to explain the composition–property relation. To account for this, we apply a recent model which incorporates knowledge of local structure, mechanical properties, and fracture patterns to predict the fracture toughness, showing a good qualitative agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Revealing the deformation mechanism of brittle materials under sharp contact loading (indentation) is important for their applications since this knowledge is crucial for identifying the origin of flaw and scratch formation on their surfaces. As a newly emerged glass family, metal–organic framework (MOF) glasses have not been studied concerning the mechanism of their indentation-induced deformation. Here, we explore this mechanism for ZIF-62 glass (a typical MOF glass system). The fractions of densification and shear flow during indentation were determined by atomic force microscopy, while the elastic deformation was measured via nanoindentation. The results show that ZIF-62 glass deforms primarily through densification and elastic deformation under the sharp contact loading. Significant pile-ups around indents were not observed, indicating that no or limited shear flow occurs in the glass during indentation. This behavior could be attributed to three structural factors, namely, high free volume, easily densified glass structure, and limited translational mobility of structural units. [ABSTRACT FROM AUTHOR]

Understanding of the fracture mechanism of metal–organic framework glasses remains limited. Using reactive molecular dynamics simulations, we here find that three zeolitic imidazolate framework glasses exhibit pronounced nanoductility upon fracture. This fracture behavior is confirmed by fracture toughness predictions. The results indicate that a model based on a purely brittle fracture significantly underestimates the simulated fracture toughness. We ascribe the nanoductility to a Zn–N bond switching mechanism, which is found to be more pronounced for smaller organic linkers. Thus, this study provides insights into the fracture mechanism of the low-toughness, yet nanoductile metal–organic framework glasses. [ABSTRACT FROM AUTHOR]

Developing less brittle oxide glasses is a grand challenge in the field of glass science and technology, as it would pave the way toward new glass applications and limit the overall raw material usage and energy consumption. However, in order to achieve this goal, more insight into the correlation between the chemical composition and material properties is required. In this work, we focus on the mechanical properties of quaternary sodium aluminoborosilicate glasses, wherein systematic changes in glass chemistry yield different resistances to indentation crack initiation. We discuss the origin of the composition dependence of indentation cracking based on an evaluation of the deformation mechanism taking place during the indentation event. To this end, we use a simple metric, the extent of indent side length recovery upon annealing, to quantify the extent of reversible volume deformation. Finally, we also compare the compositional trend in crack initiation resistance to that in crack growth resistance (fracture toughness), showing no simple correlation among the two. [ABSTRACT FROM AUTHOR]

Four different SiOC glass ceramics were synthesized and their fracture toughness (KIc) and fracture surface energy (γ) were assessed by means of the single‐edge precracked beam (SEPB) method. In addition, the elastic moduli were measured and the Vickers indentation behavior (hardness and microcracking) was characterized. In particular, the dependence of KIc on the free carbon content and on the fraction of crystallized nanoparticles (SiC, ZrO2, HfO2) was investigated. An increase in KIc, from about 0.73 to 0.99 MPa √m is observed as the free carbon content is increased from less than 1 to 12 vol%. The addition of Hf and Zr (resulting in 4.5 to 7.8 vol% HfO2 and ZrO2 nanoparticles) was found to increase KIc to an extent similar to the free carbon content. Moreover, predicted KIc values, assuming that the crack travels through all phases accounting for their respective volume fractions, disrupting the weakest links within the structural units, are in agreement with the experimental values. [ABSTRACT FROM AUTHOR]

Due to an increasing demand for oxide glasses with a better mechanical performance, there is a need to improve our understanding of the composition‐structure‐mechanical property relations in these brittle materials. At present, some properties such as Young's modulus can to a large extent be predicted based on the chemical composition, while others—in particular fracture‐related properties—are typically optimized based on a trial‐and‐error approach. In this work, we study the mechanical properties of a series of 20 glasses in the quartenary Na2O–Al2O3–B2O3–SiO2 system with fixed soda content, thus accessing different structural domains. Ultrasonic echography is used to determine the elastic moduli and Poisson's ratio, while Vickers indentation is used to determine hardness. Furthermore, the single‐edge precracked beam method is used to estimate the fracture toughness (KIc) for some compositions of interest. The compositional evolutions of Vickers hardness and Young's modulus are in good agreement with those predicted from models based on bond constraint density and strength. Although there is a larger deviation, the overall compositional trend in KIc can also be predicted by a model based on the strength of the bonds assumed to be involved in the fracture process. [ABSTRACT FROM AUTHOR]

Among the factors that influence the diversity of ectoparasites on bat hosts are the kind of roost and the host's social behavior. Other factors such as sex, reproductive condition and host size may influence the distribution and abundance of ectoparasites. The aim of the present study was to analyze the variation in Streblidae ectoparasites on the bat Phyllostomus hastatus, according to sex and roost type. We caught bats in four houses on Marambaia Island, municipality of Mangaratiba, and in one house at the Federal Rural University of Rio de Janeiro, municipality of Seropédica. We caught 65 females and 50 males of P. hastatus and 664 streblids of four species: Aspidoptera phyllostomatis, Strebla consocia, Trichobius“dugesii” complex and Trichobius longipes. The species T. longipes accounted for more than 99% of all the ectoparasites caught. Female bats were more parasitized than males, in terms of both prevalence and average intensity. The total number of parasites did not vary between resident and non-resident bats. The relationship between the number of individuals of T. longipes and sex and roost type was significant for resident bats. The total number of parasites on males did not differ between bachelor roosts and mixed-sex roosts. The differences found between roosts reflected the differences between the sexes.