Mixed conducting oxides of Nd1.8Sr0.2Ni1 - xCuxO4+ (delta) (x = 0.0, 0.2, 0.4, and 0.5) system are synthesized by combusting homogeneously mixed precursors under microwave heating. The Nd1.8Sr0.2Ni1 - xCuxO4+ (delta) solid solutions are of tetragonal structure in one single phase across the compositional range 0 <= x <= 0.5. The samples at x 0.5 are multiphase. Nd1.8Sr0.2Ni0.6Cu0.4O4.01 exhibits maximum dc conductivity (sigma = 42.7(3) S cm(-1) at 640 degrees C) and minimum activation energy (E-a = 0.07(3) eV). Minimum electrode polarization resistance value of 0.20(4) Omega cm(2) (at 700 degrees C) is obtained for Nd1.8Sr0.2Ni0.6Cu0.4O4+ (delta). Low-frequency complex impedance spectra corresponding to symmetric cells are modeled using Gerischer impedance. Oxygen partial pressure-dependent electrode polarization study suggests that the oxygen dissociation is the cathode reaction rate-limiting step. (C) 2015 Elsevier B.V. All rights reserved.