Network Modification of Glassy AlPO4: Sol-Gel Synthesis and Structural Characterization of the System Na2O–AlPO4

Abstract

Abstract Gels and glasses along the compositional tie line Na2O–AlPO4 have been synthesized using an aqueous sol-gel route, using aluminum lactate, sodium phosphate, H3PO4 and sodium acetate (NaAc) precursors. The structural evolution from the solution to gel and the final glass is monitored ex-situ by multinuclear high-resolution liquid and solid state NMR techniques. The results indicate that the aluminophosphate network structure initially formed in solution is preserved in the gel and only subsequently disrupted upon annealing above 350 °C. A structural model of the AlPO4 network modification for these glasses has been developed on the basis of compositional trends observed in the 23Na, 27Al, and 31P single and double resonance NMR spectra. Addition of the Na2O network modifier to the tetrahedral AlPO4 network reduces the extent of Al–O–P connectivity, resulting in the increased formation of Na-bound phosphate species and aluminum in higher coordination states (AlO5 and AlO6 units).