Atomic and Electronic Structure in MgO-SiO₂

Understanding disordered structure is difficult due to insufficient information in experimental data. Here, we overcome this issue by using a combination of diffraction and simulation to investigate oxygen packing and network topology in glassy (g-) and liquid (l-) MgO-SiO₂ based on a comparison with the crystalline topology. We find that packing of oxygen atoms in Mg₂SiO₄ is larger than that in MgSiO₃, and that of the glasses is larger than that of the liquids. Moreover, topological analysis suggests that topological similarity between crystalline (c)- and g-(l-) Mg₂SiO₄ is the signature of low glass-forming ability (GFA), and high GFA g-(l-) MgSiO₃ shows a unique glass topology, which is different from c-MgSiO₃. We also find that the lowest unoccupied molecular orbital (LUMO) is a free electron-like state at a void site of magnesium atom arising from decreased oxygen coordination, which is far away from crystalline oxides in which LUMO is occupied by oxygen's 3s orbital state in g- and l-MgO-SiO₂, suggesting that electronic structure does not play an important role to determine GFA. We finally concluded the GFA of MgO-SiO₂ binary is dominated by the atomic structure in terms of network topology.