Diffuse Scattering Investigations with a Graphite Double Monochromator for X-ray Synchrotron Radiation: YBa2Cu3O6.5 and KNbO3

Abstract

A graphite double monochromator for X-ray synchrotron radiation is presented for specific applications. The main feature is a broad wavelength band and a high collimation of the reflected beam. The relaxed resolution in energy results in an intensity gain of about two orders of magnitude in comparison with a high-resolution monochromator like silicon. The graphite monochromator is therefore well suited for the study of diffuse scattering. We have built and tested such a device, and have used it in combination with an image plate to record diffuse scattering distributions of single crystals with the Weissenberg and the so-called modified Laue technique. In the high Tc superconductor YBa2Cu3O6.5, the four domains of the main Bragg reflections and the two domains of the very weak diffuse superstructure reflections are clearly observed. In another application, we show the good agreement between the measured and the calculated intensities of the diffuse planes in KNbO3.