On the nature of two-dimensional short-range ordering in YBa2Cu3O7-δ

Abstract The diffuse X-ray scattering in the single crystal of YBa 2 Cu 3 O 7−δ ( δ = 0.05) is studied. It is shown that the doubling of the unit cell edge (a or b) is most probably due to the two-dimensional short-range ordering of the copper and oxygen valencies. The correlation lengths are r ⊥ ≅ 25A along the doubled edge, r t ≅ 50A in the perpendicular direction, and do not depend on the temperature.