Parallel- and perpendicular-polarized Raman, MAS, and static 31P NMR spectra were collected to investigate phosphate speciation in potassium aluminosilicate glasses. Phosphate speciation is critically dependent on the K/(K + Al) (K*) ratio. In peralkaline melts (K* = 0.75), a series of high-frequency Raman bands are assigned to phosphate structural units of different degrees of polymerization (from monomer to dimer). The 31P NMR spectra confirm the assignments. The MAS and static 31P NMR spectra indicate that P resides in an AlPO4-type environment outside the tetrahedra (SiO4)-K(AlO4) network in peraluminous melts (K* = 0.35). AlOP bonds (AlPO4 type) and KOP bonds (KPO3 type) form the dominant structural units in subaluminous melts (K* = 0.5).

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