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Glasses and glass–ceramics from the BaO–TiO2–SiO2 systems have potential applications in piezoelectric and photonic devices. However, more studies on their crystallization and mechanical properties are needed to put the materials into service. In this work, seven grades of glasses with 30BaO–xTiO2–(70-x)SiO2 (mol%) were prepared. The crystallization behavior and mechanical properties were investigated. The 30BaO–20TiO2–50SiO2 glass composition, possessing a glass transition temperature of 759 °C and a crystallization onset temperature of 877 °C, shows a prominent surface nanocrystallization. Heat treatments at 800 °C for different durations result in various depths for the crystalline phase layer. Depths of about 1 µm and 200 µm were obtained by heat treatments for 3 h and 70 h, respectively. The nucleation rate is found to be around 1016 to 1018 m−3 s−1, which is comparable to that of the fresnoite stoichiometric composition (Ba2TiSi2O8). The hardness and Young's modulus of the crystalline layer are about 100% and 50%, respectively, higher than those of the parent glass. The fracture behavior of this layer is highly anisotropic, as a result of the crystallization texture. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

• We study the structure and mechanical properties of sodium gallioborate glasses. • We compare the effect of adding Ga 2 O 3 to that of adding Al 2 O 3. • Both additions decrease the fraction of tetrahedral B units. • Ga 2 O 3 for B 2 O 3 exchange increases crack resistance, while it is opposite for Al 2 O 3. The role of Ga 2 O 3 in oxide glasses remains poorly understood compared to other network forming oxides. To address this, we here study the structure and mechanical properties of sodium gallioborate glasses and compare our findings to those of sodium aluminoborate glasses. The substitutions of both Ga 2 O 3 for B 2 O 3 and Al 2 O 3 for B 2 O 3 increase the fraction of tetrahedral Ga or Al units and decrease the fraction of tetrahedral B. However, unlike in the case of aluminoborate glasses, higher-coordinated polyhedra (i.e., GaV and GaVI) are not observed even in the pergallic region. In both glass series, most mechanical properties exhibit a change in their trend at the peralkaline-to-pergallic transition. The substitution of Ga 2 O 3 for B 2 O 3 decreases the crack initiation resistance, while the substitution of Al 2 O 3 for B 2 O 3 results in an increase in resistance. In the sodium gallioborate glasses, the fracture toughness increases in the peralkaline region and decreases in the pergallic region. [ABSTRACT FROM AUTHOR]

We show that the Single-Edge Precracked Beam (SEPB) test is not only suitable to the determination of the fracture toughness ( K Ic ) of glass, but also offers a unique opportunity to assess the slow crack growth behavior in a single experiment lasting for few minutes. Besides, we found that it is possible to get either a stable or an unstable final fracture regime (pre-cracked specimen) depending on the testing parameters, and that the unstable case is preferable for the estimation of K Ic . The "pop-in" precrack was found mostly to close completely once the load was suppressed on the bridge-flexure device. This led to a reopening event on the loading curves. It is noteworthy that all these original observations were made possible thanks to the design of a very stiff testing apparatus (6.7 MN m −1 ) allowing for a cross-head speed as small as 0.01 μm s −1 . Results obtained on four grades of commercially available glasses are compared to those stemming from Vickers indentation cracking and chevron notched experiments. [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]

Many bats use isolated houses and buildings within forested areas as daytime shelters. The large use of buildings suggests that these may be attractive for many bat species to provide protection against predators and are suitable for reproductive and social interactions. We present an overview of published (since 2000) and unpublished data (2010-2013) on the use of buildings by bats in southeastern Brazil. Thirty-one published works were analyzed. Together with the authors' data, we document 42 sites and 37 species of bats recorded to roost in buildings. Twenty-three species share shelters with other species. Molossus molossus was common in constructions of disturbed areas, was the most commonly captured insectivorous species in southeastern Brazil, and the one most frequently found under roofs. In other types of buildings, the most common species was Desmodus rotundus, observed in cohabitation with nine other species. Sampling in these roosts is important for providing data on the interactions between species. Additionally, this information could contribute to optimal management for minimizing public health problems. [ABSTRACT FROM AUTHOR]

• We show the environment dependence of K Ic for seven different glasses. • Brittle-to-ductile transition temperature is around T g. • Viscoplasticity zone is for the first time observed in experiment. • SEPB, both precracking and fracturing should be performed in inert environment. • Post-fractography in SEPB can be used to analyze the indentation cracking pattern. The role of temperature (T) and moisture on fracture toughness (K Ic) of glasses, as measured by the single-edge precracked beam method (SEPB), is investigated. The brittle to ductile temperature, shown by an increase of K Ic , is ~ T g. At T below 0.9 T g , the decrease of the bond strength with T results in the decrease of both the fracture surface energy and Young's modulus, so that K Ic decreases with T. From above T g to below 1.1 T g , the work of fracture increases because of dissipative processes, including confined viscoplasticity and blunting at the crack front. From 1.1 T g , viscous flow extends to the whole specimen and becomes more uniform, resulting in the macroscopic deformation of the specimen, eventually preventing against fracture. The results on humidity sensitive glasses show that both precracking and final fracture steps need to be performed in inert environment to meet the intrinsic K Ic value, unless the test is fast enough. [ABSTRACT FROM AUTHOR]

The resistances of glasses to crack initiation and crack growth are both important parameters for evaluating their mechanical performance. However, it is important to distinguish them as they refer to different mechanical phenomena. In this work, we study the difference in resistance to crack initiation and growth by determining the load required to induce indentation cracking (named crack resistance, CR) and the fracture toughness (K Ic), respectively, for six oxide glasses with a wide range of CR values from as low as 0.05 N to above 100 N. These new data as well as existing literature data suggest that there is no systematic relation between CR and K Ic , and as such, we conclude that these two terms should not be used interchangeably. We discuss the origin of the lacking relation by considering the competing effects of glass structure, rigidity, and atmospheric humidity on crack initiation and growth. [ABSTRACT FROM AUTHOR]

The effect of spherulitic crystallization on the elastic moduli and fracture toughness of a barium aluminum silicate glass was investigated. The crystallization process results in Ba 2 Si 3 O 8 phase and is initiated from Ba rich nuclei. Nucleation is optimal in the 690-720 °C interval. Young's modulus is increased by 12.5% when the glass-ceramic conversion is nearly complete. Nevertheless, as the size and the volume fraction of crystals are increased, some microcracking shows up upon cooling from the crystallization temperature. An optimal improvement of the fracture toughness (SEPB method) by 27 % is observed for a 49 % volume fraction of 5 to 10 μm large spherulites. [ABSTRACT FROM AUTHOR]

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. [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]

• We perform heat treatment of phase-separated modifier-free glasses. • Heat-treatment tunes the size and composition of the droplet phase. • Treatment enhances crack initiation resistance and maintains fracture toughness. • Nanoscale phase-separation can retain the high transparency of oxide glasses. In this work, we use heat treatment to vary the size of nanoscale droplets in a phase-separated B 2 O 3 -SiO 2 -Al 2 O 3 -P 2 O 5 glass without traditional modifiers and explore the effect of phase separation on the mechanical properties. The melt-quenched version of this glass already exhibits phase separation with a droplet phase rich in B 2 O 3. The glass transition temperature (T g) of the droplet phase is lower than that of silica-rich glass matrix. Upon heat treatment at a temperature below the T g of the droplet phase, the size of droplets decreases but the fraction of the droplet phase increases. Consequently, the crack initiation resistance more than doubles. Upon heat treatment at the T g of the matrix phase, the fracture toughness increases from 0.61 to 0.73 MPa·m0.5, which is primarily due to the aggregation of individual droplets. Upon the different heat treatments, the phase-separated glasses retain their optical transparency, while the hardness increases slightly. [ABSTRACT FROM AUTHOR]

The pH-dependent mechanism of the reduction of the nicotinamide adenine dinucleotide (NADH) model complex [Ru(bpy)2(5)]2+ (5 = 3-(pyrid-2'-yl)-4-azaacridine) was compared to the mechanism of the previously studied geometric isomer (Ru(bpy)2(pbn)]2+ (pbn = 2-(pyrid-2'-yl)-1-azaacridine, previously referred to as 2-(pyrid-2'-yl)-benzo[b]-1 ,5-naphthyridine) in aqueous media. The exposure of [Ru(bpy)2(5)]2+ to CO2- leads to the formation of the one-electron reduced species (k = 4.4 × 109 M-1 s-1). At pH < 11.2, the one-electron reduced species can be protonated, k = 2.6 × 104 s-1 in D2O. Formation of a C-C bonded dimer is observed across the pH range of 5-13 (k = 4.5 × 108 M-1 s-1). At pH < 11, two protonated radical species react to form a stable C-C bonded dimer. At pH > 11, dimerization of two one-electron reduced species is followed by disproportionation to one equivalent starting complex [Ru(bpy)2(5)]2+ and one equivalent (Ru(bpy)2(5HH)]2+. The structural difference between (Ru(bpy)2(pbn)]2+ and (Ru(bpy)2(5)]2+ dictates the mechanism and product formation in aqueous medium. The exchange of the nitrogen and carbon atoms on the azaacridine ligands alters the accessibility of the dimerization reactive site, thereby changing the mechanism and the product formation for the reduction of the [Ru(bpy)2(5)]2+ compound. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]