TRAPDOR NMR investigations of phosphorus-bearing aluminosilicate glasses

The local environment of phosphorus in aluminosilicate glasses of variable sodium/aluminum ratio has been investigated using double-resonance magic an gle spinning (MAS) nuclear magnetic resonance spectroscopy. The studied gla sses have the general composition xNa(2)O-(1-x)Al2O3-2SiO(2) and contain ap proximately 4 mol% P2O5 The short-range dipolar couplings of phosphorus ato ms to aluminum and sodium are used to deduce the connectivities of phosphat e units to AlO4 tetrahedra and/or sodium by observing the effects on a P-31 MAS echo spectrum caused by simultaneous irradiation of the Al-27 or Na-23 resonance frequency. In this way, different phosphorus environments were i dentified. The observed resonances can be assigned to Na3PO4 and Na4P2O7 un its, as well as phosphate tetrahedra coordinated to n aluminum atoms in the aluminosilicate framework (with n varying from 1 to 3). The results provid e unambiguous evidence for the interaction of P with aluminum even in peral kaline compositions, confirming a recently proposed model describing the so lution of phosphorus in aluminosilicate melts. (C) 1999 Elsevier Science B. V. All rights reserved.