MAS-NMR investigations of the crystallization behaviour of lithium aluminum silicate (LAS) glasses containing P2O5 and TiO2 nucleants

Lithium aluminum silicate (LAS) glass of composition (mol%) 20.4Li(2)O-4 0Al(2)O(3)-68 6SiO(2)-3 OK2 O-2.6B(2)O(3)-0.5P(2)O(5)-0 9TiO(2) was prepared by melt quenching. The glass was then nucleated and crystallized based on differential thermal analysis (DTA) data and was characterized by (29)S1, P-31, B-11 and (27)AI MAS-NMR. XRD and Si-29 NMR showed that lithium metasilicate (Li2SiO3) is the first phase to c form followed by cnstobalite (SiO2) and lithium disilicate (Li2Si2O5) Si-29 MAS-NMR revealed a change in the network structure already for the glasses nucleated at 550 degrees C. Since crystalline Li3PO4, as observed by P-31 MAS-NMR, forms concurrently with the silicate phases, we conclude that crystalline Li3PO4 does not act as a nucleating agent for lithium silicate phases. Moreover, P-31 NMR indicates the formation of M-PO4 (M=B, Al or Ti) complexes The presence of BO3 and BO4 structural units in all the glass/glassceramic samples is revealed through B-11 MAS-NMR. B remains in the residual glass and the crystallization of silicate phases causes a reduction in the number of alkali ions available for charge compensation As a result, the number of trigonally coordinated B (BO3) increases at the expense of tetrahedrally coordinated B (BO4) The (27)AI MAS-NMR spectra indicate the presence of tetrahedrally coordinated Al species, which are only slightly perturbed by the crystallization (C) 2010 Elsevier Inc. All rights reserved