Understanding Structure-Property Relations of Compressed Glasses through Relaxation Studies: Invited Talk

When a glassy material or its liquid state is subjected to sufficiently high pressure, significant changes can take place in the short- and medium-range structure, vibrational density of states, and physical properties. It is crucial to determine and understand the structure-property relations under high pressure from both scientific and technological perspectives, since the glass structures frozen-in under elevated pressure may give rise to properties unattainable under ambient pressure. However, the structural and topological origins of the pressure-induced changes in macroscopic properties are not yet well understood. Here, we address this problem by subjecting various isostatically compressed glasses to isothermal annealing at ambient pressure and monitor the relaxation of glass structure and properties as a function of time and temperature. For different glass systems, density is found to relax in a stretched exponential manner with an exponent close to the Phillips value of 3/5 for relaxation in three dimensions when both short- and long-range interactions are activated [1]. For a compressed soda lime borate glass, we find that upon annealing at 0.9Tg, the pressure-induced increase in boron coordination remains unchanged, while the pressurized values of macroscopic properties such as density, refractive index, and hardness are relaxing [2]. Hence, the pressure-induced changes in macroscopic properties are not necessarily attributed to changes in the short-range order in the glass, but rather to changes in overall atomic packing density and medium-range structures. Moreover, we show that the relaxation mechanism depends on the annealing temperature and different physical properties (e.g., density and hardness) are found to relax on different timescales.

[1] M. M. Smedskjaer, S. J. Rzoska, M. Bockowski, J. C. Mauro, Journal of Chemical Physics 140, 054511 (2014).
[2] M. M. Smedskjaer, R. E. Yougnman, S. Striepe, M. Potuzak, U. Bauer, J. Deubener, H. Behrens, J. C. Mauro, Y. Z. Yue, Scientific Reports 4, 3770 (2014).