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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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