Lars Rosgaard Jensen

The development of high-modulus glasses is essential for advanced lightweight applications, requiring a fundamental understanding of how different oxide components dictate elastic performance. To maximize stiffness, oxides must be strategically introduced to enhance both network connectivity and volumetric packing density; hence, Y2O3, ZnO, and CeO₂ are investigated here due to their high single-bond dissociation energies and strong cationic field strengths. Magnesium aluminosilicate glasses (MAS) modified with Y2O3, ZnO, and CeO2 were systematically investigated to establish composition–structure–property relationships. A constrained ternary mixture design (Y2O3–ZnO–CeO2 = 14 wt.%) was used to span the compositional space efficiently. The measured Young’s modulus ranged from 97.5 to 113.8 GPa, while the specific modulus varied between 36.6 and 41.7 ×10⁶ N·m/kg. The highest values were obtained for compositions adding Y2O3 alone or Y₂O₃–ZnO. Raman spectroscopy revealed systematic changes in the Si–O stretching band, including shifts in band position and variations in band width depending on composition. These changes indicate structural reorganization of the glass network. A correlation between Raman peak position and the specific modulus (R² = 0.24, ρ = 0.033, n = 19) indicates that structural connectivity effects contribute to stiffness, whereas the corresponding correlation with Young's modulus does not reach significance at α = 0.05 (R² = 0.19, p = 0.064). Additional factors such as packing density and cation field strength are therefore also relevant. The results show that Y2O3 is the most effective oxide for increasing stiffness, ZnO exhibits composition-dependent behaviour, and CeO2 reduces the specific modulus. The combined analysis provides an experimental and structural basis to designing high-modulus glass systems.

Melting and glass formation of metal-organic frameworks (MOFs) allow them to be processed into bulk materials. However, two major challenges remain: only a small fraction of MOF crystals undergo melting and glass-formation, and no well-established strategies exist for tuning MOF glass structures and properties. Here, we address both challenges through co-melting of zeolitic imidazole frameworks (ZIFs), a subset of MOFs, with heterocycle-based halide salts. The salt acts as a chemical “modifier”, akin to the role of alkali modifiers in traditional silicate glasses, e.g., allowing the melting of ZIF-8 that otherwise decomposes prior to melting. Through experimental and computational analyses, we show that the salts depolymerize the ZIFs, enabling continuous tuning of the fraction of bridging to non-bridging imidazolate linkers and, thereby, the thermal and mechanical properties. The proposed strategy enables diversification of MOF glass chemistry, tunable structures and properties, and ultimately an increased number of glass-forming MOFs with improved functionalities.

Methods to improve the fracture toughness of oxide glasses are needed since low fracture toughness is a major bottleneck for their applications. To overcome this, it is critically important to investigate the effect of both short- and medium-range structural features on fracture toughness. Recent work reported a record-high fracture toughness for a bulk lithium aluminoborate glass subjected to hot compression. Here, we further explore the structural origin of this high fracture toughness by subjecting different alkali aluminoborate glasses to hot compression. Through a combination of x-ray total scattering experiments and atomistic simulations, we find that hot compression causes significant changes to both the short- and medium-range order structure of the glasses, e.g., increased coordination numbers (CNs) of network forming species and decreased average size of ring-type structures. To this end, we reveal positive correlations between the pressure-induced increase in fracture toughness and (i) the increase in average CN of network forming species and (ii) the area of the first sharp diffraction peak in the structure factor. Our study thus improves the understanding of which structural features benefit intrinsic toughening of oxide glasses.