Glass Formation at the Limit of Insufficient Network Formers

TLDR

In inorganic glasses, covalent networks are normally formed, yet conventional wisdom holds that alkaline orthosilicates cannot vitrify because they lack sufficient SiO₂ to create an interconnected network. The authors produced a bulk magnesium orthosilicate glass by containerless melting and cooling. They found that distorted Mg‑O species with 4‑, 5‑, and 6‑coordination act as network formers, suggesting that similar glassy phases could exist in interstellar environments.

Abstract

Inorganic glasses normally exhibit a network of interconnected, covalent-bonded, structural elements that has no long-range order. In silicate glasses, the network formers are based on SiO4 tetrahedra interconnected through oxygen atoms at the corners. Conventional wisdom implies that alkaline and alkaline-earth orthosilicate materials cannot be vitrified, because they do not contain sufficient network-forming SiO2 to establish the needed interconnectivity. We studied a bulk magnesium orthosilicate glass obtained by containerless melting and cooling. We found that the role of network former was largely taken on by corner and edge sharing of highly distorted, ionic Mg-O species that adopt 4-, 5-, and 6-coordination with oxygen. The results suggest that similar glassy phases may be found in the containerless environment of interstellar space.