摘要
Unlike traditional silicate glasses,germanate glasses often feature non-monotonic variations in mate-rial properties(e.g.,elastic moduli and glass transition temperature)with varying chemical composition,temperature,and pressure.However,the underlying atomic-scale structural origins remain poorly under-stood.This is because,in most oxide glasses,the structural changes are quantified through solid-state NMR spectroscopy,but unfortunately the only NMR active germanium isotope(73 Ge)has very unfavor-able NMR properties.Here,we circumvent this problem by using high-energy X-ray and neutron total scattering coupled with ab initio molecular dynamics simulations as input for Reverse Monte Carlo mod-eling.In detail,we study the structure and properties of two sodium germanate glasses(10Na2 O-90GeO2 and 20Na2 O-80GeO2)subjected to permanent densification through hot compression up to 2 GPa at the glass transition temperature.While density as well as Young’s and bulk modulus increase with pressure as expected,shear modulus first increases and then decreases slightly at higher pressures.The refined atomistic structure models suggest that the glasses feature a distribution of 4,5,and 6 coordinated Ge with a majority of 4 and 5 coordinated species.Only minor changes in the Ge-O coordination occur upon hot compression,but a notable transformation of edge-to corner-sharing Ge-polyhedra is found.This anomalous polyhedral packing causes a lower number of angular constraints upon higher pressure treatment,explaining the non-monotonic trend of shear modulus with pressure.We also find that the rings become smaller and less circular upon compression,contributing to the volumetric compaction.These findings may aid the future design of germanate glasses with tailored properties and the general understanding of structure-property relations in oxide glasses.
基金
supported by grants from the European Union(ERC,NewGLASS,No.101044664)
the MSCA Postdoctoral Fel-lowship(No.101062110)from the Horizon Europe Framework Pro-gramme
the computational resources sup-plied by EuroHPC Joint Undertaking with access to Vega at IZUM,Slovenia(No.EHPC-REG-2022R02-224)
Aalborg University(No.CLAAUDIA)
Mikkel Juelsholt and Kirsten M.Ø.Jensen are grate-ful for funding from the Villum Foundation(No.VKR00015416).
