Morphology of CaF2 nanocrystals and elastic properties in transparent oxyfluoride crystallized glasses

An oxyfluoride glass with the composition of 25CaF2–5CaO–20Al2O3–50SiO2 (mol%) and crystallized glasses containing CaF2 nanocrystals (10–70 nm) are fabricated. The size and morphology of CaF2 nanocrystals is examined using transmission electron microscopy and atomic force microscopy (AFM), and elastic properties of crystallized glasses are evaluated using a cube resonance method. The large increase in the glass transition temperature in crystallized glasses suggests that the Al2O3–SiO2 based glass network having a high thermal stability is created due to the formation of CaF2 nanocrystals. It is suggested from AFM observations that the chemical bonding between CaF2 nanocrystals and oxide glass matrix is weak. Young’s modulus (E) increases with increasing heat treatment temperature, i.e., E = 88.4 GPa for the glass and E = 93.3 GPa for the sample heat-treated at 700 °C for 1 h. The present study demonstrates that oxyfluoride crystallized glasses containing CaF2 nanocrystals have good elastic (mechanical) properties, being available in practical device applications even from the mechanical point of view.

► Morphology of CaF2 nanocrystals in oxyfluoride crystallized glasses was examined.
► Elastic properties of oxyfluoride crystallized glasses were evaluated.
► Young’s modulus increases with increasing heat treatment temperature.
► The chemical bonding between CaF2 nanocrystals and oxide glass matrix is weak.