The crystal structure of YBa₂Cu₃O₆, the x = 1 phase of the superconductor YBa₂Cu₃O_7−x

Black crystals, displaying a micaccous habit, result from heating the 90 K superconducting phase YBa₂Cu₃O_7−x above 1050°C. The crystals are tetragonal, P4/mmm, a = 3.863 (2) Å, c = 11.830 (4) Å, Z = 1, ρ_cal = 6.115 g/cm³. The 184 independent single-crystal reflections were used to refine the structure by least squares to R = 0.0374, wR = 0.0347. The structure contains Cu⁺ in twofold coordination and corrugated layers of Cu²⁺–O. The Ba²⁺ is in eightfold coordination between the Cu⁺ and Cu²⁺ layers and Y is in eightfold coordination between the Cu²⁺ layers.