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

In the present work, we have discovered a new oxide-ion conductor SrYbInO 4 with CaFe 2 O 4 -type structure. SrYbInO 4 is the first example of CaFe 2 O 4 -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 SrYbInO 4 of 1.76(13) eV is lower than that of a mixed conductor CaFe 2 O 4 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 SrYbInO 4 consists of Sr and two types of double octahedra, B 2 O 10 and C 2 O 10 . Here, B and C are Yb 0.574(2) In 0.426(2) and In 0.574(2) Yb 0.426(2), respectively, which indicates partial Yb/In occupational disorder. Both B 2 O 10 and C 2 O 10 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.