Oxygen Vacancy Ordering in BaYCu3O7−x, 0 ≤ x ≤1, by Electron Diffraction Studies

Abstract

ABSTRACTElectron diffraction photographs of Ba2YCu3O7−x with x ∼ 0.15, ∼ 0.50, and ∼ 0.85, show diffuse scattering which can be attributed to the partial ordering of the oxygen vacancies. For x ∼ 0.15 and ∼0.85 it consits of continous rods which run parallel to the c* axis and whose interceptions with the basal a*b* plane can be indexed on the unit cell 2√2ac × 2√2ac × 3ac. This cell is orthorhombic or tetragonal for x ∼ 0.15 and ∼ 0.85, respectively. For the former composition every fourth O4 atom is removed from every other CulO4 chain. For the later the ordering is the same, however, the occupied oxygen positions become vacancies, and vice versa. Both orderings are uncorrelated along the c axis. For x ∼ 0.5 the diffuse scattering consits of either continuous rods or continous ribbons which run parallel to the c* axis and whose interceptions with the basal a*b* plane can be indexed on the orthorhombic unit cell 2ac × ac × 3ac. The ribbon widths are sample dependent. For this type of compounds all O4 atoms of every other CulO4 chain running along the b axis, are removed. As in the previous cases the ordering is uncorrelated along the c* axis. The ribbon elongation along the a* axis is indicative of additional disorder along this axis. This disorder seems to be related to the oxygen stoichiometry.