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Epitaxial (LaBa)Co2O5+δ thin films were grown on (001) LaAlO3 single-crystal substrates using pulsed laser deposition. Microstructure characterizations from X-ray diffraction and electron microscopy indicate that the films are highly c-axis oriented with cube-on-cube epitaxy. Transport property measurements indicate that the films have typical semiconductor behavior with a novel phase transition and hysteresis phenomena at 540 K. The chemical dynamic studies reveals that the resistance of the film changes drastically with the change of redox environment, i.e., the magnitude of resistance changes, ΔR = 1 × 102 ⇔ 1 × 106 Ω, is found within a short response time (∼700 ms). These phenomena suggest that the as-grown (LaBa)Co2O5+δ film have extraordinary sensitivity to reducing-oxidizing environment and the exceedingly fast surface exchange rate.

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AC complex impedance spectroscopy studies were conducted between 600 and 800°C on symmetrical cells that employed strontium-and-magnesium-doped lanthanum gallate electrolyte, La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 ͑LSGM͒. The objective of the study was to identify the materials system for fabrication and evaluation of intermediate-temperature ͑600-800°C͒ solid oxide fuel cells ͑SOFCs͒. The slurry-coated electrode materials had fine porosity to enhance catalytic activity. Cathode materials investigated include La 1−x Sr x MnO 3 ͑LSM͒, LSCF ͑La 1−x Sr x Co y Fe 1−y O 3 ͒, a two-phase particulate composite consisting of LSM-dopedlanthanum gallate ͑LSGM͒, and LSCF-LSGM. The anode materials were Ni-Ce 0.85 Gd 0.15 O 2 ͑Ni-GDC͒ and Ni-Ce 0.6 La 0.4 O 2 ͑Ni-LDC͒ 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°C͒, 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.