Bragg diffraction of X-rays by single crystals with large microdefects I. Generalized dynamical theory

Basic equations of the dynamical scattering theory in momentum space have b een considered in the two-beam approximation for single crystals containing randomly distributed microdefects commensurable with extinction length. Th e amplitudes of coherent and diffusely scattered waves inside the crystal h ave been found by using the perturbation theory with average and fluctuatin g parts of crystal polarizability as small parameters. In the complex dispe rsion corrections to the wave vectors of coherent and diffuse waves. the im aginary parts of which describe the attenuation of these waves due to diffu se scattering, the dynamical effects in diffuse scattering and their depend ences on the incidence angle have been taken into account. These correction s also take account of the influence of any multiple diffuse scattering pro cesses. The coherent component of crystal reflectivity has been calculated in the approximation of semiinfinite crystal for an arbitrary diffraction g eometry.