Powder diffraction experiment overnight

Overnight experiments normally take from several hours to a whole day or night. It makes sense to run these experiments overnight, since modem powder diffractometers are completely automated. Overnight powder diffraction experiments usually provide good quality diffraction patterns, which are satisfactory for further numerical processing that requires precise peak positions and their intensities. 

No powder diffraction experiment should be started at 20s = 0°, since the extremely high intensity of the incident beam at full tube power may damage the detector even when the narrowest slits have been used. The most dependable way to determine 20s for an overnight or a weekend experiment is to perform a quick scan at 5 to 10 deg/min beginning at the minimum allowable Bragg angle and ending at 20e = 30 to 40°. Based on this result, the correct 20s may be properly selected. ... 

Figure 4.1. The flowchart illustrating common steps employed in a structural characterization of materials by using the powder diffraction method. It always begins with the sample preparation as a starting point, followed by a properly executed experiment both are considered in Chapter 3. Preliminary data processing and profile fitting are discussed in this chapter in addition to common issues related to phase identification and analysis. Unit cell determination, crystal structure solution and refinement are the subjects of Chapters 5,6, and 7, respectively. The flowchart shows the most typical applications for the three types of experiments, although any or all of the data processing steps may be applied to fast, overnight and weekend experiments when justified by their quality and characterization goals.

Smoothing is a numerical conditioning procedure employed to suppress statistical noise, which is present in any powder diffraction pattern as a result of random intensity measurement errors (Eq. 3.8 in Chapter 3). It improves the appearance of the powder diffraction pattern. For example, smoothing can make quickly collected data (say in a 15 min experiment) look similar to a pattern collected in a longer (e.g. in an overnight) experiment, and may help with certain automatic procedures, such as background subtraction, Ka2 stripping and unbiased peak search. 

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