Exaggerated grain growth

Sodium ion conduction in /S"-alumina is anisotropic and ceramic electrolytes produced from this material not only can be sensitive to exposure to moisture but also are somewhat difficult to densify (e.g., because of problems related to NaaO evaporation, conversion to single-phase / -alumina, and control of exaggerated grain growth). For these reasons. Serious attempts have been made to find alternative materials that have Na" ion conductivities comparable to or higher than / "-alumina but are easier and/or potentially more economical to fabricate. Here we review attempts to develop alternatives. They fall into two classes of materials the crystalline NASICON family of compounds and conducting glasses. 

Yan, M. F. Johnson, D. W. (1978). Impurity-induced exaggerated grain growth in Mn-Zn ferrites. Journal of the American Ceramic Society, 61,342-9. 

FIGURE 24.22 Using a single-crystal sphere to model exaggerated grain growth in AI2O3 doped with 1 wt% MgO at 1800°C for 60 minutes. 

Templated growth of materials like BaTiOs presents an attractive route to producing a textured ceramic. Templated grain growth of alumina was discussed above. The principle involved here is the use of a seed to initiate exaggerated grain growth. 

---