Mechanical property optimization of a zinc borate glass by lanthanum doping

All known oxide glasses are inherently brittle, but their resistance to damage such as hardness and crack resistance varies strongly as a function of the chemical composition. The damage resistance is in turn related to the underlying deformation mechanism, which is at least partly related to the Poisson's ratio. That is, glasses with high Poisson's ratio tend to mostly deform through shear flow relative to densification, which leads to ductility in metallic glasses for Poisson's ratio above ~0.33. In this study, we investigate the structure and mechanical properties of a binary zinc borate glass with a relatively high Poisson's ratio (0.30), which we modify by partial substitution of ZnO with La ₂O ₃. Glass transition temperature, density, Vickers hardness and crack resistance, as well as elastic constants are studied, in addition to the short and intermediate range structure as probed by ¹¹B solid-state NMR and Raman spectroscopy. We find that the substitution of La for Zn leads to a monotonic increase in Poisson's ratio and elastic moduli, while local maxima are recorded in the trends of glass transition temperature, hardness, and crack resistance. Correlations between the mechanical and structural properties are discussed to shed light onto the structural origin of damage resistance in oxide glasses with high Poisson's ratio.