Oxygen ordering in the crystal structure of the 93-K superconductor YBa2Cu3O7 using powder neutron diffraction at 298 and 79.5 K

The crystal structure of the 93-K superconductor YBa2Cu3O7 has been elucidated from neutron powder diffraction data at 298 and 79.5 K. We confirm the basic features of the perovskite-related structure found at room temperature from earlier x-ray diffraction studies of small single crystals and find, additionally, that ordering of one of the oxygen atoms gives rise to square planar coordination for one of the copper atoms rather than disordered octahedral coordination. Within the resolution of our data there is no apparent change in structure below Tc.