Transmission electron microscopic (TEM) studies have revealed SrZrO3 formation and growth at La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)/Ce0.9Gd0.1O2 (GDC)/yttria-stabilized zirconia (YSZ) interfaces in solid oxide fuel cells (SOFCs). SrZrO3 forms first at the GDC/YSZ interface: at the interface between the GDC dense layer and the YSZ, at grain boundaries in the GDC dense layer, and on the surface of the GDC dense layer during the sintering of LSCF at 1100°C. Then, SrZrO3 grows to both sides of the YSZ electrolyte and the porous GDC layer. Electron energy loss spectroscopy revealed the inter-diffusion of La, Ce, and Gd as well as Sr and Zr in the vicinity of the GDC/YSZ interface. La was a solute in SrZrO3, and SrZrO3 exhibited a tetragonal crystal structure with a double pseudo-cubic perovskite sub-cell. Nucleation and growth of the SrZrO3 orthorhombic phase was observed at 800°C under an O2 atmosphere in an environmental TEM.