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The Nd 2− x Sr x NiO 4+δ (x00.1-0.5) solid solutions prepared by combustion synthesis are of submicron/superfine crystallite size. The crystal structure estimated by Rietveld analysis reveals increase in space in the rock salt layer on partial replacement of Nd 3+ by Sr 2+ . The transition from negative temperature coefficient to positive temperature coefficient of conductivity is observed at 913 K. The maximum dc conductivity (σ01.3±0.02 Scm −1 at 973 K) is obtained for x00.2 in Nd 2− x Sr x NiO 4+δ . The low dc conductivity compared with reported (≈100 Scm −1 ) is due to high porosity (low relative density) resulting from agglomeration of submicron crystallites. The variation in the conductivity with Sr content in Nd 2−x Sr x NiO 4+δ is understood on the basis of defect chemistry. The electrochemical properties of the cathode materials are studied using electrochemical impedance spectroscopy at various temperatures and oxygen partial pressures. Nd 1.8 Sr 0.2 NiO 4+δ cathode exhibits lowest-area-specific resistance 00.52 ± 0.015 Ohm cm 2 at 973 K. At low P O 2 (<1,000 Pa), oxygen ion transfer from Nd 1.8 Sr 0.2 NiO 4+δ cathode to gadolinium-doped ceria electrolyte is the rate-limiting step, whereas, charge-transfer reaction on the cathode becomes more important at high oxygen partial pressures and temperature (973 K).

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