MAS-NMR study of lithium zinc silicate glasses and glass-ceramics with various ZnO content

Lithium zinc silicate glasses of composition (mol%): 17.5Li(2)O-(72-x)SiO2-xZnO-5.1Na(2)O-1.3P(2)O(5)-4.1B(2)O(3), 5.5 <= x <= 17.7, were prepared by conventional melt-quenched technique and converted to glass-ceramic by controlled crystallization process. Si-29 and P-31 MAS-NMR was used to characterize the structure of both glass and glass-ceramic samples. Despite the complex glass composition, Q(2), Q(3) and Q(4) sites are identified from Si-29 MAS-NMR, which relative intensities are found to vary with the ZnO content, indicating a network depolymerization by ZnO. Moreover, well separated Q(3) and Q(4) resonances for low ZnO content indicates the occurrence of phase separation. From P-31 MAS-NMR, it is seen that phosphorus is mainly present in the form of ortho-(Q(0)) and pyro-phosphate (Q(1)) structural units and variation of ZnO content did not have much effect on these resonances, which provides an additional evidence for phase separation in the glass. On conversion to glass-ceramics, lithium disilicate (Li2Si2O5), lithium zinc ortho-silicate (Li3Zn0.5SiO4), tridymite (SiO2) and cristobalite (SiO2) were identified as major silicate crystalline phases. Using Si-29 MAS-NMR, quantification of these silicate crystalline phases is carried out and correlated with the ZnO content in the glass-ceramics samples. In addition, P-31 spectra unambiguously revealed the presence of crystalline Li3PO4 and (Na,Li)(3)PO4 in the glass-ceramics. (c) 2007 Elsevier Inc. All rights reserved.