Different roles of phosphorus in the nucleation of lithium aluminosilicate glasses

Glasses in the Li2O-Al2O2-SiO2 (LAS) system with different Al2O3/Li2O ratio and with or without addition of P2O5 have been synthesized and characterized by thermal analysis. The glass structure and the phosphorus environments in the glasses and their evolutions with annealing have been studied by P-31 Solid-State Nuclear Magnetic Resonance (NMR) and Al-27{P-31} D-HMQC (Dipolar Hetero-nuclear Multiple-Quantum Coherences) NMR correlation technique. The crystallization behavior has been studied by X-ray diffraction, NMR and Raman spectroscopy. The results showed a different role for P2O5 depending on the Al2O3/Li2O ratio. For low alumina content, P2O5 plays a nucleating role while it acts as crystallization inhibitor for high alumina content. These different roles are related to different local environments of the phosphorus in the as-cast glasses. Our study emphasizes the importance of POAl complexes in the crystallization of aluminosilicate glasses.