Sol-gel routes leading to nasicon ceramics

Nasicon and Titzicon compositions have been obtained as powders or monolithic, optically clear gels by sol-gel processes. Variations of the synthesis method have been explored by changing the proportion of metal organic reagents and the hydrolysis rate. The structural evolution as a function of temperature can be correlated with the specific area variations: the Nasicon phase is gradually formed between 800 and 1050°C. The target compositions were achieved with only a small Zr deficiency. The previously reported rhombohedral → monoclinic (R/M) transition is only observed in materials manufactured above 1100°C where traces of monoclinic zirconia also appear. Higher sintering temperatures give better defined R/M transitions, which shift to higher temperatures. Titzicon preparations, however, contain much vitreous phase (30%). Well-densified (>96%) Nasicon ceramics can be obtained by fast sintering (>200°C/h) at low temperatures (<900°C); thin specimens are optically translucent. However, it is necessary to establish a balance between lowering sintering temperatures and maintaining the target structural state (and properties).