  In view of the strong anisotropy of oxygen diffusion in high-Tc ceramic
YBa2Cu3Ox, it is supposed that a polycrystalline sample of this material can be
presented as consisting of crystal grains where each grain was formed by a
certain sequence of layers with tetragonal or orthorhombic phase structure. The
theory of scattering by mixed-layer crystals was taken as a basis for
calculating theoretical X-ray patterns for different sequences of the layers.
Some modifications were made in the theory due to crystal structure features of
the YBa2Cu3Ox phases. The results obtained agreed quantitatively with data
published in many papers and can be used for interpreting the X-ray patterns
from ceramics with different oxygen stoichiometry.
