Abstract: The influence of Si and Be barrier layers on the mixing of thin layers of multilayer X-ray mirrors based on Cr and Sc in a wide temperature range has been studied by X-ray reflectivity, X-ray diffraction, and transmission electron microscopy. Annealing of the Si/[Cr/Sc]200 system is found to be a catalyst of the mixing process. Complete mixing of layers occurs in a sample heated at 450°C for 1 h. The structure becomes textured with a preferred orientation [001] of the Sc layer perpendicular to the substrate. Introduction of a Be barrier layer into the Si/[Cr/Sc]200 system limits mixing of chromium and scandium layers during annealing to 350°C, but the structure degrades completely at 450°C. A beryllium barrier layer excludes texturing and growth of grains in the system, but it does not impede crystallization. The thin Si interlayer inserted between Cr and Sc layers limits their mixing and retains the multilayer character and amorphicity of the system at temperatures up to 450°C.