As discussed before, to match the shapes of the peaks, you must reproduce the broadening effects of both the diffraction instrument and effects from the sample. What determines these broadening effects and how they are introduced into the fit will be the subject of this chapter.
For some studies, determining the broadening characteristics is only needed as a means to obtain a good fit to the pattern, allowing determination of lattice or structural parameters, and indeed this was the original goal when Hugo Rietveld developed his eponymous analysis process. However, the parameter values that are used to model the peak profiles can provide information on the sample at the microscale, which can be very important for understanding the properties of a material that are not intrinsic to the substance but rather depend on how the substance was processed. Traditionally, microscopic techniques are well suited to provide the most detailed information on things like crystallite size and morphology, but Rietveld analysis has an advantage in that it provides measures that represent the entire sample bulk. Bulk characterization of a sample by microscopy is typically a very tedious process. The downside of sample characterization from powder diffraction is that it requires careful work to separate sample from instrumental effects.