New Oxide-Ion Conductor SrYbInO4 with Partially Cation-Disordered CaFe2O4-Type Structure

In the present work, we have discovered a new oxide-ion conductor SrYbInO4 with CaFe2O4-type structure. SrYbInO4 is the first example of CaFe2O4-type pure oxide-ion conductors where the oxide-ion conduction is dominant. It was found that the activation energy for the oxide-ion conduction of SrYbInO4 of 1.76(13) eV is lower than that of a mixed conductor CaFe2O4 of 3.3 eV. Rietveld analysis of neutron and synchrotron X-ray diffraction data and density functional theory (DFT)-based calculations revealed that the crystal structure of the new material SrYbInO4 consists of Sr and two types of double octahedra, B2O10 and C2O10. Here, B and C are Yb0.574(2)In0.426(2) and In0.574(2)Yb0.426(2), respectively, which indicates partial Yb/In occupational disorder. Both B2O10 and C2O10 double octahedra form infinite columns along the b axis. The bond valence based energy landscape of an o(2)(-) test ion indicates one-dimensional diffusion of oxide ions along the edges of double octahedra in the b direction.