X-ray and neutron powder diffraction data for superconducting orthorhombic ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ have been used in a joint refinement to give a room-temperature structure which includes a very precise set of atom positions and thermal-motion parameters. Broadening of the diffraction peaks indicates that these materials are highly strained, and contrary to a number of suggestions in the literature, no evidence is found for any cation disorder.

• Received 22 February 1988

DOI:https://doi.org/10.1103/PhysRevB.37.7960