Figure 5 shows the single-pulse ^{31}P MAS NMR spectra measured for the NAGP materials with x = 0: (a) as-prepared glass; (b) glass annealed at T_{TT} = 873 K for 0.25 h; (c) glass annealed at T_{TT} = 876~K for 0.5 h; (d) crystalline material.