Geometrical analysis of superstructures in YBaCo4O8.5 by electron diffraction

Two kinds of superlattice reflections from oxygenated YBaCo4O7 + δ phase are investigated based on the electron diffraction. In light of the method of the Niggli reduced cell, corresponding superstructures are determined to be a hexagonal lattice with parameters of aA = 10.90(4) Å and cA = 10.02(6) Å and an orthorhombic lattice with parameters of aB = 18.90(4) Å, bB = 10.90(5) Å and cB = 10.05(0)Å, respectively. With respect to their respective parent hexagonal structure, the two superstructures are determined to be 3×3×1 structure and 3×3×1 structure. In addition, the origin of superlattice reflections is also discussed. The study advances our understanding of structural property, the extraordinary oxygen ordering and the oxygen diffusion process in YBaCo4O7 + δ.

► We investigated two kinds of superlattice reflections from oxygenated YBaCo4O7+δ phase.
► Based on the Niggli cell method, a 3×3×1 hexagonal superstructure is determined.
► And another 3×3×1 orthorhombic superstructure is also determined.
► Such superstructures lie most possibly in the ordering of the extra oxygen in the lattice.
► The octahedra center under Kagomé Co2 triangles in (2¯10)h planes is the most possible site for extra oxygen.