TECHNIQUES FOR AB-INITIO STRUCTURE DETERMINATION FROM X-RAY-POWDER DIFFRACTION DATA

The ab initio structure determination of new materials using X-ray powder diffraction data is still in its infancy when compared with the advances that have been made in single crystal diffraction techniques. Although the powder diffraction data contain all the information that is measurable in a single crystal experiment, getting at even a small part of this information is not trivial. The ab initio structure determination requires an accurate and precise decomposition of the (usually highly) overlapped peaks in the powder pattern. The peak position information is then used for unit cell indexing, and once this is accomplished the resultant integrated intensities can be used for the structure solution. At best, the powder data are normally limited to specific zones of hkl data, only the strongest of which are represented in the powder pattern. This can translate to problems in building the structure model. An overview of the procedures, from data acquisition through to the final refined structure, will be examined.