HIGH RESOLUTION POWDER DIFFRACTION ON THE SWISS-NORWEGIAN BEAMLINE AT THE ESRF

Philip Pattison¹ Kenneth D. Knudsen, Maciej Posel²

Swiss-Norwegian beamline, ESRF, BP 220, 38043 Grenoble Cedex, France
¹Dept of Crystallography, University of Lausanne, CH-1015 Lausanne, Switzerland
²Institute of Chemistry, University of Neuchatel, CH-2000 Neuchatel, Switzerland
E-mail of presenting author: pattison@esrf.fr

Keywords: Synchrotron, powder diffraction, high resolution

The development of high-energy synchrotron sources, together with progress in new methods for structure solution based on powder diffraction data, has had a marked impact on the number and complexity of crystal structures solved from powder data. On the Swiss-Norwegian beamline (BM1B) at the ESRF, a third generation synchrotron source has been combined with optimized powder diffraction instrumentation to produce powder patterns of exceptional quality. We describe briefly the experimental arrangement, and illustrate the instrumental performance which has be achieved to date. The angular resolution in the diffraction pattern, for example, is better than 0.01^o of 2q at a typical operating wavelength of 0.7A. For ab initio structure solution, the narrow instrumental resolution reduces dramatically the effects of peak overlap at high angle, and hence increases the number of independent intensities which can be successfully extracted from the powder pattern. Examples of the application of Direct Methods to the structure solution of organic molecules will be given. Employing a cryostat opens up the possibility of studying temperature-induced phase transitions, and it can also be used to improve the signal/noise ratio for high order reflections. We have operated our helium flow cryostat routinely down to 5K, and we will presents examples of structural phase transitions observed with this equipment. In addition, we have studied high temperature order-disorder transitions in perovskites, in which the narrow instrumental broadening was particularly helpful. We believe that extremely high resolution diffractometers of this type will become a standard tool on the new generation of synchrotron sources which are currently coming on-line.