Abstract
The side bands of X-ray diffraction were investigated for the modulated structures in a Cu–Ti alloy. The side band profiles in the powder patterns were calculated by using the general diffraction theory for a one-dimensionally disordered crystal. The calculated profiles depend strongly upon the distribution of wavelengths and the wave form of modulation. The side bands are intensified and close to the fundamental reflection for the diffuse distribution of wavelengths. Daniel and Lipson formula is thought to overestimate the mean wavelength of modulation with such a diffuse distribution. The asymmetry in intensity of side bands is mainly caused by the asymmetric wave form of modulation. The experimental X-ray side band profiles were reproduced successfully by the present calculation using proper distributions of the modulation wavelengths and amplitudes. By the comparison of the experimental side band profiles with the calculated ones, it is suggested that the progress in phase separation is accompanied by broadening of the distribution of modulation wavelengths and by increasing in the degree of asymmetry of wave form as well as increasing in the mean wavelength and amplitude.
