Ordered Oxygen Arrangements in Y1Ba2Cu3O7−x

We describe the ordered oxygen arrangements in Y1Ba2Cu3O7−x samples prepared in precisely controlled oxygen environments using a solid-state ionic tehnique. The so-called “Ortho II”phase, characterized by a <1/200> superlattice wave vector, exists at oxygen contents from 6.28 to 6.65, with electrical properties that range from insulating to superconducting at up to 60 K. Additional ordered structures occur at oxygen contents from 6.65 to 6.90. All of the ordered structures are consistent with the removal of entire chains of oxygen along the b axis, which minimizes the number of three-fold coordinated copper and creates Cu+1 ions even in oxygen-rich samples. We found no evidence for phase separation between 6.0 and 7.0 or between 6.5 and 7.0. Phase separation,if it occurs at all, occurs on the 60 K and 90 K plateaus.