Line Broadening of X-Ray Diffraction XRD Peaks

X-ray diffraction patterns can be rapidly obtained with today s computerized diffractometers, and they are very informative in regard to typical dispersed metal catalysts. The high-surface-area support material usually has quite broad diffraction peaks because in its amorphous state it has limited long-range, translational order. In contrast, diffraction peaks for 

This relationship is acquired using the Scherrer equation for XRD line 

most diffractometers are not set up to obtain patterns with samples under a controlled environment, thus nearly all XRD data are obtained after exposure to air. One must ascertain that such exposure is not going to alter the reduced state of the metal significantly, which could change the diffraction pattern, and even the formation of a thin oxide overlayer on a small metal crystallite could alter the metal peak width observed. Frequently, some passivation step should be used to prevent any significant oxidation, especially with small metal crystallites that are prone to oxidation (Fe and Ni, for example). Alternatively, leak-proof XRD sample holders can be made, and reduced samples can be loaded in a dry box prior to placement in the X-ray diffractometer [17]. 

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