X-Ray Diffraction

X-ray powder diffraction (XRD) is one of the most powerful techniques for qualitative and quantitative analysis of crystalline compounds. The technique provides information that cannot be obtained any other way. The information obtained includes types and nature of crystalline phases present, structural makeup of phases, degree of crystallinity, amount of amorphous content, microstrain & size and orientation of crystallites.

When a material (sample) is irradiated with a parallel beam of monochromatic X-rays, the atomic lattice of the sample acts as a three dimensional diffraction grating causing the X-ray beam to be diffracted to specific angles. The diffraction pattern, that includes position (angles) and intensities of the diffracted beam, provides several types of information about the sample which are discussed below:

• Angles are used to calculate the interplanar atomic spacings (d- spacings). Because every crystalline material will give a characteristic diffraction pattern and can act as a unique ‘fingerprint’, the position (d) and intensity (I) information are used to identify the type of material by comparing them with patterns for over 80,000 data entries in the International Powder Diffraction File (PDF) database, complied by the Joint Committee for Powder Diffraction Standards (JCPDS). By this method, identification of any crystalline compounds, even in a complex sample, can be made.

• The position (d) of diffracted peaks also provides information about how the

atoms are arranged within the crystalline compound (unit cell size or lattice parameter). The intensity information is used to assess the type and nature of atoms. Determination of lattice parameter helps understand extent of solid solution (complete or partial substitution of one element for another, as in some alloys) in a sample.

• Width of the diffracted peaks is used to determine crystallite size and microstrain in the sample.

• The ‘d’ and ‘I’ from a phase can also be used to quantitatively estimate the amount of that phase in a multicomponent mixture.

As mentioned earlier, XRD can be used not only for qualitative identification but also for quantitative estimation of various crystalline phases. This is one of the important advantages of the x-ray diffraction technique. Several methods have been proposed and successfully used to quantify crystalline phases in mixtures. They include external standard methods, the reference-intensity-ratio (RIR) method, chemical methods and the whole pattern fitting Rietveld method. Of the available methods, the Rietveld method is probably the most accurate and reliable method.

The Rietveld method is a whole-pattern fitting least squares refinement technique and has been successfully

used for quantification and characterization of inorganic and organic compounds It has also been used for crystal structure refinement, to determine size and strain of crystallites.

X-ray diffraction has applications in most fields dealing with solid materials. XRD identifies crystalline compounds as opposed to X-ray Fluorescence (XRF) or other spectrochemical methods that identify just the elements.

Areas of application are quite wide and include metals, organic and inorganic compounds. For more information please call Sampath Iyengar atTechnology of Materials at 909.471.8194. Address: 21090 Cielo Vista Way, Wildomar , CA 92595.

	9240 Santa Fe Springs Rd Santa Fe Springs, CA 90670
info-wcas@bodycote.com	562.948.2225 Fax 562.948.5850

$X-Ray Diffraction$

Analysis of Materials by X-Ray Diffraction