International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 5.2, p. 501

Section 5.2.12. Instrumental line-profile-shape standards

W. Parrish,a A. J. C. Wilsonb and J. I. Langfordc

aIBM Almaden Research Center, San Jose, CA, USA,bSt John's College, Cambridge CB2 1TP, England, and cSchool of Physics & Astronomy, University of Birmingham, Birmingham B15 2TT, England

5.2.12. Instrumental line-profile-shape standards

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The need for standard reference materials to determine instrumental line profiles arose from the increased use in recent years of whole-pattern methods (Section 5.2.6[link]) in several applications of powder diffraction. Instrumental line-profile standards are required to determine resolution, as a check that alignment has been optimized, or to compare the performance of different diffractometers, and to obtain sample contributions from observed data in line-profile analysis. Different standards may therefore be required if samples of interest do not have a high absorption coefficient for the radiation used.

In addition to the usual requirements for SRMs, suitable substances for instrument characterization clearly should not exhibit any measurable sample broadening, even when used with high-resolution diffractometers. Various materials were considered by the Technical Committee of the JCPDS–ICDD, in association with NIST, and lanthanum hexaboride [LaB6: a0 = 4.15695 (6) Å at T = 299 K] was selected for use as an instrumental standard (Fawcett et al., 1988[link]). This was subsequently marketed by NIST as SRM 660 and it also serves as a line position standard. Other materials used as instrumental standards include BaF2 (Louër & Langford, 1988[link]) and KCl (Scardi, Lutterotti & Maistrelli, 1994[link]). Both are low-cost materials, are available in large quantities, and can readily be annealed to minimize sample broadening. Although KCl introduces a measurable contribution to line breadth owing to sample transparency, it can be used to advantage for correcting data from materials having a similar absorption coefficient, such as many ceramics. van Berkum, Sprong, de Keijser, Delhez & Sonneveld (1995[link]) selected a 5–10 µm size fraction from silicon SRM 640b, deposited about 1.5 Mg m−2 uniformly on a (510)-oriented single-crystal silicon wafer and annealed the whole assemblage to produce an instrument line-profile standard. The resulting line-profile widths were found to be slightly less than for LaB6 at angles below about 100°(2θ) with Cu Kα radiation.

References

Berkum, J. van, Sprong, G. J. M., de Keijser, Th. H., Delhez, R. & Sonneveld, E. J. (1995). The optimum standard specimen for X-ray diffraction line-profile analysis. Powder Diffr. 10, 129–139.
Fawcett, T. G., Crowder, C. E., Brownell, S. J., Zhang, Y., Hubbard, C., Schreiner, W., Hamill, G. P., Huang, T. C., Sabino, E., Langford, J. I., Hamilton, R. & Louër, D. (1988). Establishing an instrumental peak profile calibration standard for powder diffraction analyses: international round robin conducted by the JCPDS–ICDD and the US National Bureau of Standards. Powder Diffr. 3, 209–218.
Louër, D. & Langford, J. I. (1988). Peak shape and resolution in conventional diffractometry with monochromatic X-rays. J. Appl. Cryst. 21, 430–437.
Scardi, P., Lutterotti, L. & Maistrelli, P. (1994). Experimental determination of the instrumental broadening in Bragg–Brentano geometry. Powder Diffr. 9, 180–186.








































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