Training

Basic operation of a Powder X-ray Diffractometer (Rigaku Miniflex XRD)

Powder XRD (X-ray Diffraction) is perhaps the most widely used x-ray diffraction technique for characterizing materials. It utilizes the monochromatic X-rays to determine the interplanar-spacings (d-spacing) of the unknown materials. Samples are analyzed as powders with grains in random orientations to insure that all crystallographic directions are "sampled" by the beam. When the Bragg conditions for constructive interference are obtained, a "reflection" is produced, and the relative peak height is generally proportional to the number of grains in a preferred orientation.

The X-ray spectra (a 2D diffraction pattern) generated by this technique, shows concentric rings of scattering peaks corresponding to the various d-spacings in the crystal lattice. The positions and the intensities of the peaks are used for identifying the underlying structure (or phase) of the material. For example, the diffraction lines of graphite would be different from diamond even though they both are made of carbon atoms. This phase identification is important because the material properties are highly dependent on structure.

Data reduction routines rapidly determine peak position, relative intensities, and calculate intracrystalline d-spacings. The complete ASTM powder diffraction file (a database of 70,000 + known phases) is available for identification of unknown crystalline materials.

References

1. D. M. Moore and R. C. Reynolds, Jr., X-Ray Diffraction and the Identification and Analysis of Clay Minerals, Oxford University Press, New York, Ch. 1, 2, & 3. 1989. (Plenum, New York, 1992).
2. M. F. C. Ladd and R. A. Palmer, Structure Determination by Crystallography, 3rd ed., Plenum Press, New York, 1994.
3. Jens Als-Nielsen and Des McMorrow, Elements of Modern X-ray Physics, John Wiley & Sons, Ltd., 2001
4. B. E. Warren, X-ray Diffraction, General Publishing Company, 1969, 1990 (Classic x-ray physics book)
5. B. D. Cullity, Elements of X-ray Diffraction, 2nd ed., Addison-Wesley, 1978 (Covers most techniques used in traditional material characterization)
6. D. Keith Bowen and Brian K. Tanner, High Resolution X-ray Diffractometry and Topography, Taylor & Francis, Ltd., 1998 (Semiconductors and thin film analysis)
7. H. Brumberger, Editor, Modern Aspects of Small-Angle Scattering, Kluwer Academic Publishers, 1993 (SAXS techniques)
8. Jan Drenth, Principles of Protein X-ray Crystallography, Springer, 1994 (Crystallography).