X-ray studies of the YBa2Cu3O6+x superstructures in the range of 0.40(3) ≤ x ≤ 0.73(3)

By means of X-Ray diffraction on single crystals of YBa2Cu3O6+x with a well defined oxygen content it is shown that the ortho-II phase 2a0xb0 exists in the range of 0.40(3) ≤ x ≤ 0.63. The crystals with x = 0.70(3) and x = 0.73(3) possess the 3a0xb0 superstructure. Both are caused by a short-range ordering of the Cu(1)-oxygen and Cu(1)-vacancy chains. The antiparallel displacements a0xy = 0.011(1)Å, a0xBa = -0.039(1)Å, c0zCu(2) = 0.018(2)Å, and c0z0(1) = 0.049(7)Å are determined for the x = 0.58(2) by a profile refinement method.