AC complex impedance spectroscopy studies were conducted between 600 and 800 C on symmetrical cells that employed strontium-and-magnesium-doped lanthanum gallate electrolyte, La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM). The objective of the study was to identify the materials system for fabrication and evaluation of intermediate-temperature (600-800 degrees C) solid oxide fuel cells (SOFCs). The slurry-coated electrode materials had fine porosity to enhance catalytic activity. Cathode materials investigated include La1-xSrxMnO3 (LSM), LSCF (La1-xSrxCoyFe1-yO3), a two-phase particulate composite consisting of LSM-doped-lanthanum gallate (LSGM), and LSCF-LSGM. The anode materials were Ni-Ce0.85Gd0.15O2 (Ni-GDC) and Ni-Ce0.6La0.4O2 (Ni-LDC) composites. Experiments conducted with the anode materials investigated the effect of having a barrier layer of GDC or LDC in between the LSGM electrolyte and the Ni-composite anode to prevent adverse reaction of the Ni with lanthanum in LSGM. For proper interpretation of the beneficial effects of the barrier layer, similar measurements were performed without the barrier layer. The ohmic and the polarization resistances of the system were obtained over time as a function of temperature (600-800 degrees C), firing temperature, thickness, and the composition of the electrodes. The study revealed important details pertaining to the ohmic and polarization resistances of the electrode as they relate to stability and the charge-transfer reactions that occur in such electrode structures. (c) 2005 The Electrochemical Society.