Na1 + xAlxGe2 − xP3O12 (x = 0.5) glass–ceramic as a solid ionic conductor for sodium ion

• A Na+-conducting glass–ceramic containing crystalline NASICON phase was successfully prepared.
• Al cation enters the structure of NASICON by replacing Ge4 + ions.
• The highest sodium ionic conductivity of the glass–ceramic is up to 9.27 × 10− 5 S cm− 1 at 140 °C.
• The reasons for the increase of the ionic conductivity in the glass–ceramic are discussed.

Sodium-ion conducting glass–ceramics composed of Na1 + xAlxGe2 − xP3O12 (x = 0.5) crystalline conducting phase were successfully prepared by heat-treating the parent glass at different temperature and time, and were characterized with DSC, XRD, CV, SEM and alternative current impedance. The relationship between the ionic conductivity and crystallization conditions (time and temperature) of the sodium aluminum germanium phosphate (NAGP) glass–ceramic was investigated. Results show that the NASICON phases containing Al3 + in all these glass–ceramics are isomorphous with NaGe2P3O12 and stable against sodium metal. The highest total conductivity of the glass–ceramic material, 9.27 × 10− 5 S cm− 1 at 140 °C, is obtained by highly crystallizing the glass at 750 °C for 12 h. The reasons for the enhancement of the ionic conductivity in the glass–ceramics are discussed in view of the dependence of microstructure morphology on the heating condition. It could be attributed to its good crystallization of the conductive phase NAGP, uniform grain size and possible optimizing conductive pathway of Na+ ions.