Fitting of full X-ray diffraction patterns is an
effective method for quantifying abundances during X-ray diffraction (XRD)
analyses. The method is based on the principal that the observed diffraction
pattern is the sum of the individual phases that compose the sample. By adding
an internal standard (usually corundum) to both the observed patterns and to
those for individual pure phases (standards), all patterns can all be
normalized to an equivalent intensity based on the internal standard intensity.
Using least-squares refinement, the individual phase proportions are varied
until an optimal match is reached. As the fitting of full patterns uses the
entire pattern, including background, disordered and amorphous phases are
explicitly considered as individual phases, with their individual intensity
profiles or “amorphous humps” included in the refinement. The method can be
applied not only to samples that contain well-ordered materials, but it is
particularly well suited for samples containing amorphous and/or disordered
materials. In cases with extremely disordered materials
where no crystal structure is available for Rietveld refinement or there is no
unique intensity area that can be measured for a traditional RIR analysis,
full-pattern fitting may be the best or only way to readily obtain quantitative
results. This approach is also applicable in cases where there are several
coexisting highly disordered phases. As all phases are considered as discrete
individual components, abundances are not constrained to sum to 100%.
References
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