Diffuse X-ray scattering from a calomel crystal near the temperature of the structural phase transition

X-ray scattering from a calomel crystal near the temperature of a structural phase transition is analyzed theoretically. It is shown that the diffuse lines of the x-ray diffraction, which correspond to both the X points and Z point of the Brillouin zone, are formed in the high-temperature phase. The latter lines result from the scattering by the beats of fluctuations of two components of the order parameter. Such lines were previously observed experimentally, but the nature of the lines corresponding to the Z point remained unclear. It is shown that the Z line at the point (5, 0, 0) should be an order of magnitude stronger than the observed Z line at the point (4, 3, 0).