Structural change around Si atoms in P₂O₅-SiO ₂ binary glasses before and after annealing by²⁹Si MAS NMR spectroscopy

The ²⁹Si MASNMR spectra of P₂O₅-SiO ₂ binary glasses were measured before and after annealing to examine the local structure around Si atoms in the glasses. The glasses were composed of SiO₆ octahedra and Q₄ (SiO₄ tetrahedra with four bridging oxygens). By increasing the P₂O₅ content, the fractions of SiO₆ octahedra increased and those of Q₄ decreased. The fractions of SiO₆ octahedra increased by 6-8% in the range of 29.7 to 47.4 mol % P₂O₅ by annealing for 5 h. This result was found for the first time in binary glasses. On the basis of the results obtained, the local structure around Si atoms in the glasses and the structural change by annealing are discussed.