It is well established that the ionic diffusion in a given glass depends on the field strength of different ions. The diffusion of Al3+ ion is slower than that of Zn2+ in present work, due to the difference in field strength (1.77 for Al3+ and 0.91 for Zn2+).19 and 20 Therefore, the diffusion of Al3+ from the bulk of glass–ceramics to the interface increases with longer heat-treatment time, which leads to the increasing Al/Zn ratio at the interface when the heat-treatment time increases from 7 days to 30 days. In addition, the greater fraction of solid solution phase at the sealing interface than that in the bulk of glass–ceramics (Fig. 5 and Fig. 6) can be attributed to the enhanced diffusion of Al3+ ions by the presence of oxygen vacancy in doped-ceria ceramics. Moreover, the smaller Al/Zn ratio in both glass–ceramics (Table 1) and reaction couples (Table 2) with increasing ZnO dopant can be related to the accelerated diffusion of Zn2+ ions in glasses with greater concentration gradient of Zinc.21