Polycrystalline powders, Bragg reflection

There are many ways to build a model of the crystal structure of a polycrystalline material without first using the intensities of individual Bragg reflections, which are hidden in powder diffraction due to partial or complete overlapping. Most of the direct space approaches are, in effect, trial-and-error methods and they include some or all of the following components ... 

Preferred orientation is a problem encountered when using powder diffraction methods. It occurs when most of the crystallites in a polycrystalline sample have a nonrandom distribution of orientations, resulting in only a certain number of the Bragg reflections moving into the reflecting position and thus contributing disproportionately to the scattered intensity. Ideally, the crystallites should be randomly... 

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