Mixed ionic-electronic conductors can be used in applications like permeation membranes and fuel cell electrodes. Reduction stability and oxygen permeability are two of the major features deciding about the use of an MIEC-composition in a certain application. From this reason different compositions belonging to the K2NiF4-type structure (Ln(2)Ni(0.8)Cu(0.2)O(4) Ln = La, Pr, Nd) were synthesized and characterized regarding their reduction stability in nitrogen as well as in reducing atmosphere. Furthermore disc-shaped samples of a definite thickness and surface roughness were manufactured and characterized regarding their oxygen permeability in an air-nitrogen/oxygen partial pressure gradient. (C) 2008 Elsevier B.V. All rights reserved.