Ordered to defect fluorite structural transition in Ce_1-xNd_xO_2-δ system and its influence on ionic conductivity

The structural transformation from fluorite – defect fluorite – hexagonal phase on the heavily doped ceria system (Ce_1-xNd_xO_2-δ X = 0, 25, 50, 75 and 100 mol%) has been investigated in this study. The oxygen ionic conductivity increased with dopant content till 50 mol% due to the formation of rare earth C-type superstructure defect fluorite. The co-formation of rare earth C-type structure along with the fluorite increase the anion vacancies and facilitates the barrier free ion migration. The long-range ordering and the existence of mixed phases in the heavily doped (75 mol%) system lowered the oxide ion conductivity. Ce_0.5Nd_0.5O_1.75 in disordered fluorite structure exhibits a superior ionic conductivity of 6.0 mS/cm with an activation energy of 0.93 eV which has a potential as electrolyte in solid oxide fuel cells application.