Characterisation of a new NZP material prepared from reactive sintering of a phosphate based glass

NZP materials are based on the NaZr2(PO4)3 type structure, but are difficult to fabricate into monoliths, due to the high temperatures and long sintering times required for the synthesis. We propose reactive sintering of a phosphate based glass (60NaPO3.20SnO.20WO3) as an alternative route to prepare a new tungsten (IV) and tin (IV) containing crystalline compound with the NZP structure. Using various techniques, we have shown that different parameters influence the achievement of a single crystalline phase with the NZP structure, such as the initial glass composition, glass particle size or curing atmosphere. Compared to the parent glass, the glass-ceramic exhibits an important increase of Tg and of the dilatometric softening point. The elastic properties are also enhanced, while the coefficient of thermal expansion decreases. Leaching tests show that NZP phase is not soluble, in contrast to the glass phase. Indexing of the diffraction pattern was carried out in order to determine the unit cell parameters and the space group. Rietveld refinement of the diffraction pattern, combined with analysis by energy-dispersive x-ray spectroscopy, demonstrates that tungsten is incorporated on a mixed tin and tungsten site, and almost 90% of these octahedral MIVO6 sites are occupied by Sn4+ ions, and the remaining 10% by W4+ ions.