New glasses in the alumina-calcia-monazite (LaPO$_{4})$ system: structural evidence from NMR, Raman scattering and thermal properties

A new group of glasses has been synthesized from the well-known compounds CaAl$_{2}$O$_{4}$ and (CaO)$_{12}$(Al$_{2}$O$_{3})_{7}$, melted together with monazite (LaPO$_{4})$ in compositions containing 2 to $>$75{\%} of the latter. Raman and $^{31}$P NMR spectra in the solid state show that PO$_{4}$ groups do not share bridging oxygens, i.e. that the materials are orthophosphates. Thermal properties and $^{27}$Al NMR in both liquid and solid states indicate the presence of a strong aluminate network, based upon AlO$_{4}$ tetrahedra sharing corners. P/Al TRAPDOR NMR measurements show that P and Al are in close proximity in the glasses, most likely sharing P-O-Al linkages. However, clear and unambiguous signatures of the aluminate network are still sought. Models for the structures of these glasses, drawn from experiment, will be presented.