Preparation of partially Y- or Yb-substituted SrFeO3- with cubic perovskite structure and its electrical conduction properties

SrFeO 3- δ prepared in air exhibits a tetragonal or orthorhombic perovskite crystal structure with an ordered distribution of oxide-ion vacancies at room temperature. Changing the crystal structure to cubic perovskite with a random distribution of oxide-ion vacancies is expected to improve the hole or oxide-ion conductivity. In this study, the crystal structure of SrFeO 3- δ was altered by partially substituting Y or Yb at the Sr or Fe sites. X-ray diffraction and X-ray absorption spectroscopy revealed that Y partially substituted only at the Sr site, whereas Yb could substitute at both the Sr and Fe sites. Both substitutions resulted in a cubic perovskite structure. Mössbauer spectroscopy detected charge delocalization from the Y- or Yb-substitution in the cubic phase. The degree of delocalization was higher in the Sr-site-substituted specimen than in the Fe-site-substituted specimen. The cubic phases of Sr 1- x Y x FeO 3- δ , Sr 1- x Yb x FeO 3- δ , and SrFe 1- x Yb x O 3- δ exhibited a semiconducting temperature dependence devoid of phase transition effects. The lower electrical conductivity of SrFe 1- x Yb x O 3- δ compared with that of Sr 1- x Yb x FeO 3- δ corresponded to the lower delocalization degree observed by Mössbauer spectroscopy. Sr 0.9 Y 0.1 FeO 3- δ and Sr 0.9 Yb 0.1 FeO 3- δ exhibited electrical conductivity comparable with that of cubic SrFeO 2.75 above 420 °C without the structural phase transition influence, indicating their application potential, e.g., for gas separation and electrodes in solid oxide fuel cells. • Cubic Sr 1- x Y x FeO 3- δ , Sr 1- x Yb x FeO 3- δ , and SrFe 1- x Yb x O 3- δ (0.1 ≤ x ≤ 0.2) were prepared. • Mean Fe valence of cubic phase was almost 3.50+ regardless of the substitution site. • Charge in Sr 1- x Y x FeO 3- δ and Sr 1- x Yb x FeO 3- δ delocalized more than in SrFe 1- x Yb x O 3- δ. • Delocalization is the cause of higher conductivity in Sr 1- x Ln x FeO 3- δ ( Ln :Y, Yb). • The influence of the phase transition was not observed in electrical conductivity.