The structure of aluminophosphate glasses revisited:: Application of modern solid state NMR strategies to determine structural motifs on intermediate length scales

In this paper we report a reinvestigation of the network organization in aluminophosphate glasses. Samples were prepared along the 50K(2)O-xAl(2)O(3)-(50-x)P2O5 composition line with 0 < x < 20%. The evolution of the glass structure upon alumina incorporation into the phosphate network is monitored employing a combination of advanced solid state NMR strategies including P-31{Al-27}-CP-HETCOR NMR, P-31[Al-27-REAPDOR NMR, Al-27{P-31}-REDOR NMR and 2D P-31-J-RESolved NMR spectroscopy. Details of the employed NMR protocol are given elsewhere. The network organization on intermediate length scales as a function of the alumina content is then described employing a modified Q notation, Q(m,AlOx)(n), where n denotes the number of connected tetrahedral phosphate, m gives the number of aluminate species connected to a central phosphate unit and x specifies the nature of the bonded aluminate species (i.e., AlO4-, AlO5- or AlO6-species). (c) 2007 Elsevier B.V. All rights reserved.