Preferred Orientation

Many materials form in such a way that their grains are not randomly oriented with respect to each other. A good example is Mica (Phyllosilicate), where the planes align parallel to each other and undergo basal cleavage, forming thin and uniform sheets.

Many materials such as metals, minerals, thin films and polymers will adopt a Preferred Orientation (PO) when formed. Some will also develop a texture when subsequently processed. In most cases, PO will lead to anisotropic distribution of properties such as modulus, strength, ductility, toughness, electrical conductivity, thermal expansion, etc. Therefore, it is important to monitor and quantify changes in the texture.

X-ray diffraction is an ideal tool to examine preferred orientation. In a conventional θ/2θ coupled scan, preferred orientation will cause a change in the intensity distribution. Such changes can be quantified with the Texture Coefficient, which compares the oriented sample to the ideal unoriented sample. A more complete picture of the orientation is obtained by the use of Pole Figures and Orientation Distribution Functions.

Among the many uses of Texture Analysis are:

  • Properties in thin films
  • Forgings
  • Surface coatings
  • Optimizing growth conditions
  • Formation of epitaxial layers
  • Surface and bulk deformation