Powder diffraction with synchrotron radiation. II. Dispersion factors of Ni

Abstract

Accurate values of the absolute integrated reflections from a powder sample of Ni have been determined from measurements with synchrotron radiation as a function of scattering angle over a range of energies from 290 to 3 eV below the Ni K-absorption edge, 8332 eV. From these values, the dispersion factor f' has been determined by comparison of the experimental scattering factors with the theoretical values of Wang & Callaway [Phys. Rev. B. (1977), 15, 298- 306] based upon a LCAO calculation with the KSG (Kohn & Sham and Gaspar) approximation for exchange [Kohn & Sham (1965). Phys. Rev. 140, A1133-1138; Gaspar (1954). Acta Phys. Acad. Sci. Hung. 3, 263-286]. The values obtained for f' as a function of energy are within about 0.2 electron units of those calculated from measured and tabulated absorption coefficients by Bonse & Hartmann-Lotsch [Nucl. Instrum. Methods (1984), 222, 185-188] and within about 0.5 electron units of their direct measurements by interferometric techniques in the range 30 to 3 eV below threshold. The variation of f' with scattering angle is negligibly small (less than 0.2 electron units on average). The present experiment demonstrates that powder techniques provide a simple and convenient method for the measurement of f' for many materials that are not available in forms suitable for the application of other techniques such as interferometry.