What is it about?

This diffractometer was built to remove all the problems associated with sample alignment and peak position uncertainty. Data can be collected instantaneously, and the analysis to identify crystal structures performed in parallel to produce results in seconds. It is a ¼ of the size of a conventional Bragg-Brentano instrument with similar width diffraction peaks and has the advantage of a monochromatic probing beam based on Cu Kα1. The resolution can be increased by moving the detector further from the sample.

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Why is it important?

This conventional theory of X-ray diffraction cannot explain the results from this instrument, whereas they can be explained by the “new” theory of X-ray diffraction (Fewster (2014) Acta Cryst. A70 257-282). Many new opportunities can be exploited by reassessing the theory, e.g., using exceedingly small powder samples and still achieve a useful diffraction profile.

Perspectives

This was an exciting piece of work because it demonstrated that Bragg’s law is not necessary to obtain a meaningful X-ray diffraction pattern. The instrument was built by my co-author from scratch with inexpensive components, apart from the detector and X-ray source. The testing and alignment required care until we fully understood all the sensitive parameters, with a combination of modelling and trial and error. The 2D detector used helped in the alignment and determining the exact location of the sample scattering for further statistical analysis. We were both surprised how quickly and simply a useful dataset was obtained. Consequent work with John Anderson indicated the speed and reliability of multiple phase analysis, and the complete instrument calibration to achieve <0.010 peak location for analysis.

Dr Paul F Fewster

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This page is a summary of: A compact high-resolution X-ray powder diffractometer, Journal of Applied Crystallography, November 2013, International Union of Crystallography, DOI: 10.1107/s0021889813027313.
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