The Ruddlesden-Popper (RP) phases La2Ni1-xFexO4+delta (x = 0.02, 0.1) and La4Ni3-xFexO10-delta (x = 0.3, 0.9) were successfully synthesized via the sol-gel route. Even though X-ray diffraction did not show any secondary phases for La2Ni0.9Fe0.1O4+delta, approximately 5-10% of the higher order RP phase La4Ni2.1Fe0.9O10-delta were detected in backscattered electron contrast imaging, whereas La2Ni0.98Fe0.02O4+delta exhibits no foreign phases. This was also confirmed by transmission electron microscopy (TEM). Furthermore, the oxygen permeation performance and electrical conductivity of La2Ni1-xFexO4+delta were found to decrease slightly with increasing iron content. The Mossbauer spectra of La2Ni1-xFexO4+delta (X=0.02, 0.1) are dominated by a quadrupole-split doublet. With increasing temperature, however, a minority iron species is detected. The dominating doublet reveals an unusual high-temperature behavior of quadrupolar interactions, which was observed by in-situ Mossbauer measurements at high temperatures and different oxygen partial pressures. This is most likely related to ordering phenomena of oxygen. (C) 2012 Elsevier B.V. All rights reserved.