OXYGEN ORDERING AND TWEED STRUCTURE IN YBA2CU3O6-SCATTERING(X STUDIEDBY DIFFUSE NEUTRON)

A comprehensive study of oxygen ordering and of the associated lattice distortion in YBa2Cu3O6+x is presented as obtained by diffuse neutron -scattering techniques. Within a range of concentration, 0.5 < x < 0.6 4, a short-range-ordered OII structure is found to be stable. Upon hea ting from room temperature the scattering intensity diminishes rapidly and disappears completely near 150-degrees-C. Furthermore, the existe nce of a tweedlike structure is confirmed within the orthorhombic phas e. The tweed intensity varies with the amount of the orthorhombic spli tting and is considerably reduced in the tetragonal phase.