Theoretical study of the properties of X-ray diffraction moire fringes. I

A detailed and comprehensive theoretical description of X-ray diffraction moire fringes for a bicrystal specimen is given on the basis of a calculation by plane-wave dynamical diffraction theory. Firstly, prior to discussing the main subject of the paper, a previous article [Yoshimura (1997). Acta Cryst. A53, 810-812] on the two-dimensionality of diffraction moire patterns is restated on a thorough calculation of the moire interference phase. Then, the properties of moire fringes derived from the above theory are explained for the case of a plane-wave diffraction image, where the significant effect of Pendellosung intensity oscillation on the moire pattern when the crystal is strained is described in detail with theoretically simulated moire images. Although such plane-wave moire images are not widely observed in a nearly pure form, knowledge of their properties is essential for the understanding of diffraction moire fringes in general.