Room-temperature structure of the 90-K bulk superconductor ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{8\mathrm{-}\mathrm{x}}$

The 90-K superconducting phase of Y-Ba-Cu-O has been isolated, and its structure at room temperature determined by single-crystal x-ray diffraction. The material is an oxygen-defect perovskite, with composition ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8\mathrm{-}\mathrm{x}}$. Entire planes of oxygen atoms between copper atoms are missing from the perovskite structure. The result is a quasi-two-dimensional structure in which sandwiches of ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8\mathrm{-}\mathrm{y}}$ are separated by layers of Y.