Crystallization and sodium-ion conduction properties of glass-ceramic solid solutions of Na5FeSi4O12 and Na4ZrSi4O12

This study focused on the effect of Zr-inclusion on Na[Formula: see text] conduction properties of the newly developed glass–ceramic solid solutions of Na 5 FeSi 4 [Formula: see text] and Na 4 ZrSi 4 [Formula: see text]. We experimentally confirmed formation of an all proportional solid solution in the range of [Formula: see text]= 0 and 1.0 with the composition Na[Formula: see text]Fe[Formula: see text][Formula: see text]Si 4 [Formula: see text]. Glass–ceramic with a fast Na[Formula: see text]-conducting Na 5 YSi 4 [Formula: see text]-type single phase was obtained in all the solid solutions. The conduction properties of the glass–ceramics were improved with increasing content of Zr, and Na 4 ZrSi 4 [Formula: see text] was the most conductive glass–ceramic. The ionic conductivities were as high as 1.9 × 10[Formula: see text] S cm[Formula: see text] and 9.3 × 10[Formula: see text] S cm[Formula: see text] at temperatures of 25 ∘ C and 300 ∘ C, respectively. The improved conductivity was attributed to the expansion of the conduction path by larger Zr ions replacing FeO 6 octahedra.