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Common Origin of Thermo-Mechanical Anomalies in Different Network Glasses

Liping Huang and John Kieffer. Department of Materials Science & Engineering, University of Michigan, 3062 H.H. Dow, Ann Arbor, MI 48104

Using molecular dynamics (MD) simulations, we have elucidated the structural origin of several long-standing problems in glass science, such as the anomalous thermo-mechanical properties (e.g., elastic moduli increase upon heating and decrease upon compression), irreversible densification, and polyamorphic transitions in network glasses. These simulations have been facilitated by the development of a reactive force field that realistically accounts for the charge redistribution associated with changes in bonding structure, and accommodates multiple coordination states during the MD simulations. Our simulations show that the anomalous thermo-mechanical behaviors can be explained by analogous mechanisms, whether the network structures are formed from tetrahedral or trigonal structural units (as demonstrated for amorphous silica and boron oxide). Accordingly, the origin of atypical temperature and pressure dependencies of materials properties is universal, and hence, structures can be engineered to create materials with tunable thermal and mechanical properties.