Impedance studies of dense polycrystalline thin films of La2NiO4+δ

Abstract

The cathodic kinetics of 3000 Å thick La₂NiO_4+δ (LNO) films were studied using AC impedance spectroscopy at 400–620 °C and in 0.01–1.0 atm O₂. The dense polycrystalline LNO films were deposited on both sides of yttrium stabilized zirconia (YSZ) (100) single crystal substrates by pulsed laser deposition (PLD). Three distinct features were observed in their AC impedance spectra. The high frequency (HF) feature is assigned to the oxygen ion conduction of the YSZ electrolyte, the medium frequency (MF) feature to the interfacial resistance between the film and the electrolyte, and the low frequency (LF) feature to the oxygen reduction reaction at the film surface. For the LNO film, we conclude that the electrode reaction is limited by the surface exchange reaction. The surface exchange coefficient, k_i, is calculated from the LF resistance. The values of k_i agree well with those obtained previously for a ceramic sample.