Impact of Spark Plasma Sintering on the Ionic Conductivity of La‐Doped NaNbO 3

ABSTRACT Oxide‐ion‐conducting electrolytes are pivotal for intermediate‐temperature solid oxide fuel cells (IT‐SOFC). In this work, La‐doped NaNbO 3 (Na (1‐3x) La (x) NbO (3‐δ) ) ceramics were synthesized by conventional sintering ( x = 0, 0.05, 0.075, and 0.10) and by spark plasma sintering (SPS) of undoped i.e., (NaNbO 3 ), and optimally doped ( x = 0.075) compositions. Comprehensive structural, microstructural, chemical, and electrochemical characterizations were performed to investigate the effect of La substitution and SPS on ionic transport. Rietveld refinement of x‐ray diffraction data confirmed the coexistence of orthorhombic Pbma and P2 1 ma phases, while bond‐valence‐sum analysis indicated enhanced oxygen under‐bonding with La substitution. Conductivity spectra follow Jonscher's universal power law and indicate a correlated barrier hopping conduction mechanism. Among the conventionally sintered samples, x = 0.075 exhibited the highest conductivity and was therefore selected for SPS processing. SPS‐processed Na 0.775 La 0.075 NbO 3‐δ achieved a maximum total conductivity of 4.88 × 10 −3 S cm −1 at 700°C. Electron paramagnetic resonance (EPR) validates the presence of oxygen vacancies, and x‐ray photoelectron spectroscopy (XPS) analysis confirmed an increased concentration of oxygen vacancies with La‐doping, while DC polarization measurements indicated that ion transport is the dominant conduction mechanism. These findings demonstrate the potential of SPS‐processed La‐doped NaNbO 3 as a promising solid oxide electrolyte for IT‐SOFC.