Fig. 2. Selected characteristics of the bilayer electrolyte.

(A) TEM micrograph of the 2 mol % Fe-added YSZ/GDC bilayer electrolyte after sintering at 1250°C (Fig. 1E). (B) Diffraction patterns in the selected regions [1 to 4 marked by yellow squares in (A)] obtained via FFTs. The given numbers are the lattice parameters calculated from the corresponding diffraction patterns. (C) EDS maps for Gd, Ce, Y, and Zr at the Fe-YSZ/GDC interface to examine the interdiffusion (ID) layer. (D to I) Fe composition across the GBs in Fe-YSZ [(D) to (F), region 6 in (A)] and GDC [(G) to (I), region 7 in (A)] measured by APT. TEM micrographs of needle-shaped samples before APT analysis (D and G), APT 3D reconstruction of atomic Fe species (E and H), and concentration contour maps for Fe in which the red and purple colors correspond to higher and lower concentrations, respectively (F to I).