Silica incorporation into sodium aluminum phosphate glasses: Structural characterization by Raman spectroscopy and multinuclear solid-state NMR

Abstract

Optical fiber glasses in the system (59-xP2O5)-xSiO2–13Al2O3-28Na2O show non-linear trends in the glass-transition temperatures, thermal expansion coefficients, and weathering stabilities. The structural origins have been studied using solid-state NMR and Raman spectroscopies on a series of bulk glasses with 0 ≤ x ≤ 13. Two types of P2 units – those dominantly interacting with Na+and those interacting more strongly with Al can be differentiated by 31P{23Na} and 31P{27Al} double resonance experiments. Silicon is four-coordinated, fully polymerized, and engaged in Si-O-P linkages. Trends in the 29Si chemical shifts and the 31P-31P dipolar interaction strengths are related to the Si-O-P, Si-O-Al, and P-O-P connectivity distributions, providing a rationale for changes in macroscopic properties.