Figure 3.

(a) Schematics of a pore moving with the grain boundary and possible material-transport mechanisms (blue: surface diffusion, green: lattice diffusion, and red: evaporation/condensation). (Reprinted with permission from [40]. Copyright 2003 CRC PRESS LLC). (b) A pore moving along with the grain boundary at the moment of separation from the boundary (NaNbO₃ sintered for 2 h at 1350 °C; scanning electron microscopy (SEM) image) (Reprinted with permission from [45]. Copyright 2011 The American Ceramic Society).