Structural deformation in oxidized and reduced YBa2(Cu1−yCoy)3O6+x compounds (0<y≤0.05)

We have investigated in detail the structural properties of the system YBa2 CuPin1−y Coy)3O6+x with different values of x and y. X-ray diffraction shows that the Co doping induces an orthorhombic-to-tetragonal transition at y≈0.025. Electron diffraction and electron microscopy indicate that for y<0.025, displacement fields oriented along the 〈110〉 directions exist throughout the crystallite. For y0.025 electron diffraction shows the presence of intense streaks of diffuse scattering located at the tails of the Bragg reflections in the (001) plane of the reciprocal space, and oriented along the 〈110〉 directions. For the same oxidation treatment the size of the diffuse streaks increases with increasing dopant concentration. They disappear when the sample undergoes a reduction. Two-beam images show a contrasted cross-hatched pattern whose hatchings are also oriented along the 〈110〉 directions. These features are displacive in origin and correspond to the superposition of transverse displacement fields whose propagation vectors are oriented along the 〈110〉 directions.