27Al NMR is used to quantify coordination changes in CaAl 2O 4 glass pressure cycled to 16 GPa. The structure and coordination environments remain unchanged up to 8 GPa, at which 93% of the recovered glass exists as four-fold Al, whereas the remaining population exists as [5,6]Al. Upon densification, [5,6]Al comprises nearly 30% of observed Al, most likely through the generation of three-coordinated oxygen. Negligible changes are observed for the isotropic chemical shift ( Al ? 78.8 ppm, Al ? 46.3 ppm, Al ? 12.6 ppm) and average quadrupole coupling strengths with pressure. 3QMAS spectra suggest less distortion within the newly formed Al environments in comparison with Al. The chemical shift of Al suggests that the aluminate network remains fully polymerized in glasses quenched from pressures up to 16 GPa.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films