The intermediate operating temperature solid oxide fuel cells (SOFCs) are actually under research; one of the system developments consists in adding an interlayer between the electrodes and the electrolyte materials. In the cathodic sequence, one possible solution to improve the electrochemical performance consists of a yttria-stabilized zirconia (YSZ) and a samaria-doped ceria (SDC) bilayer. But this layer sequence is still problematic due to solid-state reactions and interdiffusion at the YSZ/SDC interface. The phase formation and element diffusion have been studied when samples are sintered at different atmospheres (oxidizing, inert, and reducing) and temperatures (1100, 1200, and 1300 degrees C) by X-ray powder diffraction, scanning electron microscopy/energy dispersive X-ray analysis/wavelength dispersive X-ray analysis, and electrochemical impedance spectroscopy. The reaction and interdiffusion are preceded by the migration of the cerium to the YSZ lattice. Structural, microstructural, and electrochemical results can be improved when the deposited SDC is sintered at 1200 degrees C in air atmosphere. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3133244] All rights reserved.