New analytical approximation of diffraction size broadened peak profile for spherical crystallites with a lognormal distribution

A new analytical approximation of the diffraction peak size profile due to the lognormal distribution of spherical crystallites is derived. In comparison with the existing approximation constructed with the condition of conserving the volume-averaged column length of the exact profile [Popa & Balzar (2002). J. Appl. Cryst. 35, 338-346], the new approximation conserves both volume- and area-averaged column lengths. Moreover, it is a better approximation for large distribution dispersions. Like the old approximation, the present one is appropriate for implementation in the whole powder pattern fitting codes, Rietveld included.