6-Coordinated Si⁴⁺ in SiO₂-PO_5/2 Glasses

²⁹Si MAS NMR Method

Abstract

²⁹Si MAS NMR spectra were measured in SiO₂-PO_5/2 crystals and glasses. MAS NMR spectrum of SiP₂O₇ crystal indicated only one peak at about -215ppm, which was assigned to 6-coordinated Si⁴⁺. In the spectrum of Si₅O(PO₄)₆ crystal, two peaks were observed at about -215ppm and -120ppm. The latter was assigned to 4-coordinated Si⁴⁺. In 28mol% PO_5/2 72mol% SiO₂ glass, only the peak at about -120ppm was found and 4-coordinated Si⁴⁺ was present. The amount of 6-coordinated Si⁴⁺ was zero or very small. In 50mol% PO_5/2-50mol% SiO₂ glass, the MAS NMR spectrum indicated two peaks at about -120ppm and -215ppm. Both 4-coordinated and 6-coordinated Si⁴⁺ coexisted in this glass.