Nuclear magnetic resonance investigations of aluminum containing phosphate glass-ceramics

Glasses and glass-ceramics of the system P2O5–CaO–Na2O–{Al2O3} have been studied by 31P and 27Al and two-dimensional correlation nuclear magnetic resonance. The basic glasses have a chain-like structure including amorphous diphosphate and longer chains having at least four units. The Q1/Q2 group ratios depend on both the content of network-modifying oxides and aluminum oxide. Crystallization of the glasses involves the conversion of glassy metaphosphate sites into crystalline pyro- and orthophosphate sites. 27Al correlation experiments do not detect the presence of Al–O–Al bonds in the glasses and in the glass-ceramics.