Superionic conducting Na5SmSi4O12-type glass-ceramics: Crystallization condition and ionic conductivity

Glass-ceramics of the phosphorus-containing Na5RSi4O12 (N5)-type (R = rare earth element; Sm) Na+-superionic conductors (NaRPSi) were prepared by crystallization of glasses with the composition Na3.9Sm0.6P0.3Si2.7O9. The optimum conditions for crystallization were discussed with respect to the conduction properties and the preparation of uncracked N5-type glass-ceramics. Most of the N5-type NaSmPSi compounds were obtained as uncracked glass-ceramics when the heating time for nucleation was more than 6 h. Also studied were the microstructural effects on the conduction properties, which were dependent upon the heating conditions of crystallization. Large enhancement of electrical conductivity was observed in the glass-ceramics as the grain growth was promoted with the increase of the heating time for crystallization. The ionic conductivity of the glass-ceramic Na3.9Sm0.6P0.3Si2.7O9 heated at 900 °C for 42 h was 9.07 × 10−2 S/cm at 300 °C.