Volume and structural relaxation in compressed sodium borate glass

Area of Science:

• Materials Science
• Solid State Chemistry
• Glass Science

Background:

• Glass properties can be altered by compression near the glass transition temperature (Tg).
• These modifications are typically lost upon annealing at ambient pressure.
• Understanding the relationship between structural relaxation and property changes is crucial.

Purpose of the Study:

• To investigate the correlation between local and medium-range structural relaxation and property relaxation in compressed glass.
• To study the volume and structural relaxation of sodium borate glass after pressure quenching and subsequent annealing.

Main Methods:

• Pressure quenching of sodium borate glass at Tg from 1 GPa.
• Annealing at ambient pressure under varying temperature-time conditions.
• Analysis using 11B Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and Raman spectroscopy.

Main Results:

• Pressure-induced densification involves conversion of six-membered rings to non-ring trigonal boron (BIII) units (medium-range order) and increased tetrahedral boron (BIV) fraction (short-range order).
• These structural changes are reversible during annealing near Tg but depend on annealing temperature.
• Structural unit conversions alone do not explain densification; packing of units is the primary mechanism.

Conclusions:

• The study elucidates the complex interplay between structural rearrangements and property relaxation in compressed glass.
• Packing of structural units, rather than just conversions, is identified as the key driver for pressure-induced densification.
• Findings provide insights into controlling and understanding glass behavior under varying pressure and temperature conditions.