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

Abstract

Lithium zinc silicate glasses of composition (mol%): 17.5Li 2O–(72− x)SiO 2– xZnO−5.1Na 2O−1.3P 2O 5−4.1B 2O 3, 5.5⩽ x⩽17.7, were prepared by conventional melt-quenched technique and converted to glass-ceramic by controlled crystallization process. 29Si and 31P 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 29Si 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 31P 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 (Li 2Si 2O 5), lithium zinc ortho-silicate (Li 3Zn 0.5SiO 4), tridymite (SiO 2) and cristobalite (SiO 2) were identified as major silicate crystalline phases. Using 29Si MAS-NMR, quantification of these silicate crystalline phases is carried out and correlated with the ZnO content in the glass-ceramics samples. In addition, 31P spectra unambiguously revealed the presence of crystalline Li 3PO 4 and (Na,Li) 3PO 4 in the glass-ceramics.