Resolution investigations of X-ray three-crystal diffractometers

The object of this study is the resolution of a three-crystal difffractometer (TCD) using perfect crystals as monochromator and analyser. It relates to the resolution as a function of the scattering vector Q. This information is crucial for the interpretation of high-resolution X-ray diffraction data obtained very close to reciprocal-lattice points. In this light we present the experimentally determined resolution of TCDs using silicon 111 as well as germanium 111 and 311 reflections, respectively. The values are compared with calculations based on recently published models.