부산대학교 도서관

Atomistic simulations of the structures and defect energetics of two mixed-conducting strontium ferrite materials, Sr2Fe2O5and Sr4Fe6O13, are reported. Oxygen Frenkel defects are found to be the predominant intrinsic defects in both materials, with the Frenkel energy in the intergrowth structure, Sr4Fe6O13, being much less than that in Sr2Fe2O5or other known oxide ion conductors. Formation of electronic defects under oxidizing and reducing conditions is calculated to be more favourable in the Sr4Fe6O13intergrowth structure than in Sr2Fe2O5. Comparison of solution energies for cobalt incorporation shows Sr4Fe6O13has a slight preference for Co2being located on lower coordination sites, whereas in Sr2Fe2O5, Co2ions located on tetrahedral sites are most favourable. Binding energy calculations suggest the possible formation of Co2–vacancy clusters with increasing Co2concentration. The rapid oxide ion conductivity in Sr4Fe6−xCoxO13±δmembranes is thought to arise from a combination of factors: a low oxygen Frenkel energy to produce an intrinsic population of mobile interstitial oxide ions and vacancies, low migration energy barriers, and ease of distortion of polyhedra.