Parametric Powder Diffraction
The rapidity with which powder diffraction data may be collected, not only at neutron and X-ray synchrotron facilities but also in the laboratory, means that the collection of a single diffraction pattern is now the exception rather than the rule. Many experiments involve the collection of hundreds and perhaps many thousands of datasets where a parameter such as temperature or pressure is varied or where time is the variable and life-cycle, synthesis or decomposition processes are monitored or three-dimensional space is scanned and the three-dimensional internal structure of an object is elucidated. In this paper, the origins of parametric diffraction are discussed and the techniques and challenges of parametric powder diffraction analysis are presented. The first parametric measurements were performed around 50 years ago with the development of a modified Guinier camera but it was the automation afforded by neutron diffraction combined with increases in computer speed and memory that established parametric diffraction on a strong footing initially at the ILL, Grenoble in France. The theoretical parameterisation of quantities such as lattice constants and atomic displacement parameters will be discussed and selected examples of parametric diffraction over the past 20 years will be reviewed that highlight the power of the technique.
KeywordsRelaxation Rate Rietveld Refinement Powder Diffraction Data Neutron Powder Diffraction Ammonia Borane
We would like to thank our colleagues, Richard Ibberson (ISIS, now NIST), Takasuke Matsuo (Osaka) and Graham Stinton (Durham, now Edinburgh) for their collaboration in the C60 and WO3 parametric diffraction studies discussed in this chapter. We particularly would like to thank and acknowledge the huge contribution that Alan Coelho has made that underpins this work. His computer program, Topas, is simply crucial in enabling the most complex parametric diffraction experiments to be analysed and understood.
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