Voigt function fit of X-ray and neutron powder diffraction profiles

The Voigt function fit to the experimental powder diffraction profiles of Ni, measured with neutrons and X-rays, is studied. In the neutron case the instrumental factors are dominant while the X-ray profiles are determined by the size and strains of the crystallites. The neutron diffraction profiles fit very well down to an intensity level of 10^-2 to 10^-3 of the peak value; the improvement is an order of magnitude over the Gaussian fit. In the X-ray case, the overall fit is satisfactory, but the Voigtian fails to account properly for particle size and strain broadening simultaneously. It is concluded that the fitting parameters do not correspond to the physical measurements of the crystallites.