International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.3, pp. 266-267

Section 3.3.4. Peak profiles for X-ray energy-dispersive experiments

R. B. Von Dreelea*

aAdvanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439–4814, USA
Correspondence e-mail: vondreele@anl.gov

3.3.4. Peak profiles for X-ray energy-dispersive experiments

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In an X-ray dispersive powder diffraction experiment, a detector with good energy-discrimination capability is placed at a fixed scattering angle while the sample is illuminated by a `white' beam of radiation. The detector response is binned into discrete energies by a multichannel analyser (MCA) (Glazer et al., 1978[link]). Typically these instruments display peaks that are purely Gaussian in shape with quite low resolution (ΔE/E ≃ 1%) and have widths that are proportional to the energy:[\Gamma_G =UE + W.\eqno(3.3.24)]

This is most useful for experiments with very limited angular access (e.g. high-pressure multi-anvil setups, as described in Chapter 2.7[link] ) using synchrotron radiation and can give very high data collection rates on very small samples. Glazer et al. (1978[link]) showed that simple crystal structures can be modelled with the Rietveld technique after suitable corrections to account for the variation in source intensity, detector response and sample absorption effects. Otto (1997[link]) expanded the peak-profile description to include possible sample-broadening effects via a Voigt profile; this extended the expression in equation (3.3.24)[link] by adding a second-order term in energy and allowed extraction of size and microstrain sample-broadening effects in cases where these were large.

A related alternative technique (Wang et al., 2004[link]) collects multiple energy-dispersive powder patterns over a narrow and coarse angular step scan; this is easily done in a typical multi-anvil high-pressure setup. The array of spectra are binned as multiple angle-dispersive patterns which are then combined into a single refinement; the complex corrections required for pure energy-dispersive patterns reduce to refinable scaling factors. Typically a scan over 10° 2θ with 0.1–0.2° steps suffices to give suitable data; binning into ΔE/E ≃ 20% energy bands gives data that are used in a conventional multiple-data-set Rietveld refinement.

References

Glazer, A. M., Hidaka, M. & Bordas, J. (1978). Energy-dispersive powder profile refinement using synchrotron radiation. J. Appl. Cryst. 11, 165–172.Google Scholar
Otto, J. W. (1997). On the peak profiles in energy-dispersive powder X-ray diffraction with synchrotron radiation. J. Appl. Cryst. 30, 1008–1015.Google Scholar
Wang, Y., Uchida, T., Von Dreele, R., Rivers, M. L., Nishiyama, N., Funakoshi, K., Nozawa, A. & Kaneko, H. (2004). A new technique for angle-dispersive powder diffraction using an energy-dispersive setup and synchrotron radiation. J. Appl. Cryst. 37, 947–956.Google Scholar








































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