Abstract
The Rietveld profile analysis method has been extended using a Fourier analysis of line profiles on the basis of the Warren-Averbach method for separating size and strain effects. Assuming a given size distribution (Cauchy) and an adjustable strain variation in space, this method allows the simultaneous determination of the structural parameters and the size and strain parameters of the sample. It has been used for analysing the neutron diffraction pattern of β-LaNi 5 deuteride which exhibits a strongly anisotropic broadening. The mean coherency domain was chosen as an ellipsoid of revolution along the c axis. The structure is described in the space group P6 3 mc as well as the P31 c space group with five types of interstitial sites (three in the hypothetical fully ordered LaNi 5D 7 phase). The strain parameter, i.e. the distribution of atomic positions around their equilibrium positions, varies by a factor of 2.5 while the mean particle size changes from 80 Å to more than 2500 Å in [ hk0] and [00 l] directions respectively.
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