Interactive Tutorial about Diffraction
Powder diffraction: preferred orientation

Powder diffraction
Few crystals
Powder pattern
Preferred orientation
Pair distribution function

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In the previous examples, the individual powder grains were randomly orientated. In practice (e.g. no spherical grains) the individual grains of a powder sample can show a preferred orientation which has a significant influence on the intensity distribution of the diffraction pattern.

The left image above shows the previous pattern obtained from 200 randomly orientated grains. The middle image shows the diffraction pattern obtained from 200 randomly oriented crystals. The right images shows the diffraction pattern of 200 crystals with preferred orientation. The [100] direction of the crystals is Gaussian distributed around the [100] direction of real space. The sigma of the distribution was set to 3.0 degrees. The powder diagram along [h00] for the random orientations (blue curve) and for the preferred orientation example (red curve) are shown in the right figure. Despite the identical number of reflections, several powder lines are completely missing and the intensity of other lines is very misleading. Preferred orientation can substantially alter the appearance of the powder pattern. It is a serious problem in experimental powder diffraction.

© Th. Proffen and R.B. Neder, 2003