Structure determination thermal diffuse scattering

The residual difference after a successful DDM refinement or/and decomposition can be considered as a scattering component of the powder pattern free of Bragg diffraction. The separation of this component would facilitate the analysis of the amorphous fraction of the sample, the radial distribution function of the non-crystalline scatterers, the thermal diffuse scattering properties and other non-Bragg features of powder patterns. The background-independent profile treatment can be especially desirable in quantitative phase analysis when amorphous admixtures must be accounted for. Further extensions of DDM may involve Bayesian probability theory, which has been utilized efficiently in background estimation procedures and Rietveld refinement in the presence of impurities.DDM will also be useful at the initial steps of powder diffraction structure determination when the structure model is absent and the background line cannot be determined correctly. The direct space search methods of structure solution, in particular, may efficiently utilize DDM. 

The structure factors of InP were determined using samples compacted by pressures of 2500 kfg/cm but the intensities of the 220 and 440 reflections were corrected for the preferential orientation. These corrections were found by comparing the relative intensities obtained for samples which were not compressed with the intensities found for the compacted samples. Corrections were also made for the thermal diffuse scattering [4]. The extinction effects were slight because we used very fine powders. The linear absorption coefficient jtt was assumed to be 993 cm [5]. The polarization factor was foimd from the expression [6]... 

Bragg s law (and therefore, the coherent elastic differential cross section) can be exploited for determining the precise crystalline structure. Obviously, neutron scattering from crystals is not restricted to the coherent elastic contribution scattering observed in between Bragg peaks is called diffuse scattering, which is generally connected to some sort of disorder (thermal. 

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