X-ray powder diffraction (XRD) is an efficient analytical technique used to identify and characterize unknown crystalline materials, where monochromatic X-rays are used to determine the interplanar spacings of the unknown materials. The samples are analyzed as powders whose grains are randomly orientated to ensure that all crystallographic directions are "sampled" by the beam. When the Bragg conditions for constructive interference are obtained, a "reflection" is produced whose relative peak height is generally proportional to the number of grains in that preferred orientation.

The XRD spectra generated by this technique thereby provide a structural fingerprint of the unknown sample. Mixtures of crystalline materials can also be analyzed, and relative peak heights of multiple materials may be used to obtain semi-quantitative estimates of the abundances. A glancing X-ray beam may also be used to obtain structural information of thin films on surfaces. In addition, changes in peak position signifying either compositional variation (i.e., solid solution) or structure-state information (e.g., order–disorder transitions, exsolution, etc.) are readily detectable. Peak positions are reproducible to 0.02 degrees.

Photo of X-ray Powder Diffraction Spectrometer

Data reduction routines rapidly determine the peak position and relative intensities, and calculate intracrystalline d-spacings. The complete ASTM powder diffraction file is available on-line for identification of unknown crystalline materials.

The advantages of XRD are:

  • Rapid identification of materials
  • Ease of sample preparation
  • Computer-aided material identification
  • Large library of known crystalline structures
  • Multi-sample stage

 

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