Crystallography and microstructure of Y₁Ba₂Cu ₃O_9-x, a perovskite-based superconducting oxide

We have investigated the crystallography and microstructure of Y 1Ba2Cu3O9-x with transmission electron microscopy and x-ray diffraction. Y1Ba2Cu 3O9-x is a distorted, oxygen-defect perovskite with ordering of the yttrium and barium ions. Its unit cell is orthorhombic with space group Pmm2 and lattice parameters a=3.893 Å, b=11.688 Å, and c=3.820 Å. The structure is heavily twinned on {101} type planes, possibly due to a tetragonal-to-orthorhombic transition above room temperature.