Characterizing pressure-induced coordination changes in CaAl ₂O ₄ Glass Using ²⁷Al NMR

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 ( ^[4]Al ? 78.8 ppm, ^[5]Al ? 46.3 ppm, ^[6]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 ^[4]Al. The chemical shift of ^[4]Al suggests that the aluminate network remains fully polymerized in glasses quenched from pressures up to 16 GPa.