Effect of Ni doping on structural, electrical and electrochemical properties of Nd1.8Ce0.2Cu1 − xNixO4 + δ mixed ionic–electronic conductor

• Nd1.8Ce0.2Cu1 – xNixO4, when x = 0.0 – 0.9 synthesized by combustion yield sub-micron size grains
• Single phase solid solutions with tetragonal cuprate forms when x< 0.5 and nickelate when x> 0.5
• Minimum ASR obtained when x = 0.5 is attributed to highest dc conductivity
• Nd1.8Ce0.2Cu0.5Ni0.5 may be a potential cathode material

Mixed conducting oxides of Nd1.8Ce0.2Cu1 − xNixO4 + δ for varying values of x = 0.0, 0.1, 0.3, 0.5, 0.7 and 0.9 were synthesized by combusting mixed precursor materials under microwave heating. The Nd1.8Ce0.2Cu1 − xNixO4 + δ solid solutions are tetragonal structures in one single phase across the composition range, but it is convenient to divide the range into tetragonal Nd2CuO4 — cuprate for compositions corresponding to x ≤ 0.5 and while for x > 0.5, the same phase is described as tetragonal Nd2NiO4 — nickelate compositions. In this Nd–Ce–Cu–Ni–O system, the maximum d.c. conductivity σ = 0.619 S cm− 1, at a selected temperature of 700 °C, was obtained at a composition corresponding to x = 0.5, represented by the chemical formula Nd1.8Ce0.2Cu1 − xNixO4 + δ. At this composition, the lowest value of activation energy (Ea = 0.11 eV) was measured over a temperature range of 500 to 700 °C. Symmetric cells in the configuration given by— electrode/electrolyte/electrode—, with Nd1.8Ce0.2Cu1 − xNixO4 + δ (for x = 0.3, 0.5 and 0.7) as the electrodes were fabricated by spin coating. The minimum area specific resistance (ASR) value of 0.44 Ω cm2 was obtained at a temperature of 700 °C, for the solid solution corresponding to x = 0.5 and directly correlating with the maximum in d.c. conductivity.