The perovskite-type materials, Ln(2)NiO(4+delta), were prepared by a modified Pechini method and their electrochemical properties investigated using ac impedance and dc polarization methods from 300 to 800 degrees C under different oxygen partial pressures. Schouler methodology based on the frequency relaxation has been used to assign different electrochemical processes. A transfer process related to oxygen ions moving between the electrolyte and electrode interface was found in the mixed ionic and electronic conducting electrode/electrolyte system. The study shows that the Nd1.95NiO4+delta compound exhibits promising electrode properties due to its high chemical stability and low polarization resistance. The oxygen diffusion process is the rate-limiting step at low oxygen partial pressure, whereas the charge-transfer process becomes more important at higher oxygen partial pressure. (c) 2006 The Electrochemical Society.