Module 5 : Modern Characterization of materials

Lecture 32: Powder X - ray diffraction

Diffraction patterns are best reported using dhkl and relative intensity rather than 2q and absolute intensity.

•The peak position as 2q depends on instrumental characteristics such as wavelength.

–The peak position as dhkl is an intrinsic, instrument-independent, material property.

  • Bragg's Law is used to convert observed 2q positions to dhkl.

•The absolute intensity, i.e. the number of X-rays observed in a given peak, can vary due to instrumental and experimental parameters.

–The relative intensities of the diffraction peaks should be instrument independent.

  • To calculate relative intensity, divide the absolute intensity of every peak by the absolute intensity of the most intense peak, and then convert to a percentage. The most intense peak of a phase is therefore always called the “100% peak”.

–Peak areas are much more reliable than peak heights as a measure of intensity.