Oxygen transport kinetics of the misfit layered oxide Ca3Co4O9+δ

The oxygen transport kinetics of the misfit-layered cobaltite, Ca3Co4O9+delta, known for its thermoelectric properties, was investigated by combined application of O-18/O-16 isotope exchange and electrical conductivity relaxation techniques. Although oxygen diffusion is found to be two orders of magnitude lower than in well-investigated lanthanum nickelates, e. g., La2NiO4+delta, the mixed ionic-electronic conductor Ca3Co4O9+delta is found to exhibit fast surface exchange kinetics (k* = 1.6 x 10(-7) cm s(-1) at 700 degrees C to be compared to 1.3 x 10(-7) cm s(-1) for the nickelate), rendering it a promising electrode for application as an air electrode in solid oxide cells. In parallel, the chemical nature of the outermost surface of Ca3Co4O9+delta was characterized by means of Low Energy Ion Scattering (LEIS) spectroscopy. The absence of cobalt at the sample's outermost surface suggests that the Ca2CoO3-delta rock salt layers in the structure may play a key role in the oxygen exchange mechanism.