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This study provides atomic scale insight to understand the role of aliovalent dopants on oxygen vacancies clustering and dissociation mechanism in ceria system in order to enhance the performance of oxy-ion conductor. Dopants induced microscale changes in ceria are probed by extended X-ray absorption fine structure spectroscopy, X-ray absorption near edge spectra, and Raman spectroscopy. The results are explored to establish a correlation between atomic level structural changes (coordination number, interatomic spacing) → formation of dimer and trimer type cation-oxygen vacancies defect complex (intrinsic and extrinsic) → dissociation of oxygen vacancies from defect cluster → ionic conductivity temperature. It is a strategic approach to understand key physics of ionic conductivity mechanism in order to reduce operating temperature of electrolytes for intermediate temperature (300–450 °C) electrochemical devices for the first time.

The work provides key insight of extrinsic and intrinsic oxygen vacancies clustering, dissociation mechanism and their influence on oxy-ion conductivity in co-doped ceria system. For present attempt, we develop aliovalent co-doped ceria system Ce 0.85 Ca 0.15/2 M 0.15/2 O 2-δ (M = Sm, Gd, Nd Dy and Sr) with optimize compositions as electrolytes for IT-SOFCs. Structure of all samples are confirmed by X-ray diffraction (XRD) and analyzed by Rietveld refinement using Full-Prof suite. Oxygen vacancies clustering are observed by X-ray absorption techniques (EXAFS & XANES) and Raman spectroscopy. Two separate Raman mode related to extrinsic and intrinsic oxygen vacancies defect spaces are detected; dissociation of oxygen vacancies from the defect clustering are realized from systematic decrease in intensity of the respective Raman mode with temperature. The EXAFS study demonstrates reduction in coordination number with enhancement in interatomic spacing, and disorder factor with increasing temperature. The results are evidenced for oxygen vacancies dissociation from cluster. XANES study reveals co-dopants in ceria causes: (i) suppression of reducing ability of Ce 4+ to Ce 3+ and (ii) asymmetric distribution of Ce-O in CeO 8 polyhedron. Oxy-ion conductivity of co-doped ceria systems are determined by using complex impedance spectroscopy. Co-dopant induced atomic-scale restructuring and oxygen vacancies dissociations are found strongly influence on conduction mechanism.

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Signature of oxygen ion conductivity in hydrothermally synthesized Ce 1−x La x O 2−δ (0 ≤ x ≤ 0.50) solidelectrolyte samples has been investigated. Room-temperature Raman spectroscopy clearly shows the presence of intrinsic and extrinsic defect modes related to oxygen vacancies. Evidence of delocalization of oxygen vacancies has been analyzed through the combination of temperature-dependent Raman spectroscopy and optical absorption spectroscopy for the first time in these solid ionic conductors. Therefore, the temperature-dependent softening of oxygen defect mode in Raman spectroscopy and broadening of a feature related to oxygen defects in optical absorption spectroscopy can be an efficient tool to probe the signature of oxygen ion conductivity.