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[EN] Glass-ceramics feature excellent mechanical properties but tend to lack transparency due to the presence of large crystals with a different refractive index from the matrix glass. Here, we investigate the relationship between the heterogeneous microstructure, mechanical properties (hardness, crack resistance, and fracture toughness), and transparency in Na2O–P2O5–SiO2 glass-ceramics. The mechanical properties are determined by the combination of crystal type, content, and size, as well as the remaining glass-matrix structure. The crystal fraction and size increase upon heat treatment, whereas the network connectivity of the residual glass-matrix phase decreases. These observed changes have opposite effects on crack resistance and fracture toughness. Changes in crystallization behavior have a more significant effect on crack resistance relative to that on fracture toughness, while changes in crystal size have a more pronounced effect on fracture toughness. The glass-ceramic samples feature excellent transmittance and reach a maximum fracture toughness of 1.1 MPa m 0.5.

Metal-organic framework glasses feature unique thermal, structural, and chemical properties compared to traditional metallic, organic, and oxide glasses. So far, there is a lack of knowledge of their mechanical properties, especially toughness and strength, owing to the challenge in preparing large bulk glass samples for mechanical testing. However, a recently developed melting method enables fabrication of large bulk glass samples (>25 mm3) from zeolitic imidazolate frameworks. Here, fracture toughness (KIc) of a representative glass, namely ZIF-62 glass (Zn(C3H3N2)1.75(C7H5N2)0.25), is measured using single-edge precracked beam method and simulated using reactive molecular dynamics. KIc is determined to be ~0.1 MPa m0.5, which is even lower than that of brittle oxide glasses due to the preferential breakage of the weak coordinative bonds (Zn-N). The glass is found to exhibit an anomalous brittle-to-ductile transition behavior, considering its low fracture surface energy despite similar Poisson's ratio to that of many ductile metallic and organic glasses.

Metal-organic framework glasses feature unique thermal, structural, and chemical properties compared to traditional metallic, organic, and oxide glasses. So far, there is a lack of knowledge of their mechanical properties, especially toughness and strength, owing to the challenge in preparing large bulk glass samples for mechanical testing. However, a recently developed melting method enables fabrication of large bulk glass samples (>25 mm3) from zeolitic imidazolate frameworks. Here, fracture toughness (KIc) of a representative glass, namely ZIF-62 glass (Zn(C3H3N2)1.75(C7H5N2)0.25), is measured using single-edge precracked beam method and simulated using reactive molecular dynamics. KIc is determined to be ~0.1 MPa m0.5, which is even lower than that of brittle oxide glasses due to the preferential breakage of the weak coordinative bonds (Zn-N). The glass is found to exhibit an anomalous brittle-to-ductile transition behavior, considering its low fracture surface energy despite similar Poisson's ratio to that of many ductile metallic and organic glasses.