Journal of the American Ceramic Society, Vol.103, No.9, 4969-4982, 2020
Structural evolution at short and medium range distances during crystallization of a P2O5-Li2O-Al2O3-SiO2 glass
Li2O-Al2O3-SiO2 (LAS) glass-ceramics have important industrial applications and bulk nucleation is usually achieved by using nucleating agents. In particular, P2O5 is an efficient agent in glasses containing a low level of Al2O3 but its role in the first stages of nucleation is not well established. In this study, we combine structural investigations from local to mesoscales to describe the structural evolution during crystallization of LAS glass-ceramics. Local environment is probed using Si-29 and P-31 MAS-NMR, indicating organization of P in poorly crystallized Li3PO4 species prior to any crystallization. To better understand the detailed nanoscale changes of the glass structure, P-31-P-31 DQ-DRENAR homonuclear correlation experiments have been carried out, revealing the gradual segregation of P atoms associated with the formation of disordered Li3PO4. Small-angle neutron scattering data also show the apparition of nanoscale heterogeneities associated with Li3PO4 species upon heating treatments and allow the determination of their average sizes. These new structural information enhance our understanding of the role of P in nucleation mechanisms. Nucleation is initiated by gradual change in P environment implying P segregation upon heating treatments, forming disordered Li3PO4 heterogeneities. The segregation of P atoms enables the precipitation of meta- and disilicate phases.