SINGLE-CRYSTAL X-RAY-DIFFRACTOMETRY USING SYNCHROTRON-RADIATION

The outstanding properties of synchrotron radiation, in particular its high brilliancy over a wide spectral range, its low divergence, its p olarization properties, and the pulsed time structure, extend the rang e of single-crystal X-ray diffractometry to experiments which are not feasible with conventional sources, such as sealed X-ray tubes or rota ting anode equipment. Data collection techniques are strongly influenc ed by the general aims of a diffraction experiment, by the sample qual ity, its absorption and scattering power, as well as by the reflection profile shape and the instrumental resolution function. Often, the sa mple properties play a crucial role, and not all samples may be suitab le for data collection with synchrotron X-rays. The time-dependence of the primary beam intensity and of its polarization state requires mon itoring and normalization to monitor counts, which complicates data co llection and data reduction due to sources of both random and systemat ic errors not known from conventional X-ray sources. There is almost n o utilization of X-ray diffraction that cannot profit from the use of synchrotron radiation. X-ray diffraction at a synchrotron radiation so urce can yield structure factors of an unprecedented quality, provided proper attention is given to sample properties, to data collection st rategy and data evaluation procedures. Though little is gained for str ong reflections, the improvement is very pronounced for the weaker ref lections, including high-order reflections, which can be measured in m uch shorter time than with conventional X-ray sources. However, synchr otron radiation does not provide a solution to all problems, in some c ases conventional laboratory X-ray sources may be more appropriate tha n synchrotron radiation. Taking into account the limited access to syn chrotron radiation sources, X-ray diffraction with synchrotron radiati on can only supplement, but not replace conventional X-ray sources and diffraction techniques.