The Calibration of Laboratory X-Ray Diffraction Equipment Using NIST Standard Reference Materials
James P. Cline, David R. Black, Donald A. Windover, Albert Henins
The laboratory X-ray powder diffractometer offers several virtues that have rendered it a principal characterization device providing critical data for a range of technical disciplines. A continuous suite of hkl reflections can be collected with a single scan in angular space. Practical data collection rates can be realized with the use of a divergent beam that can illuminate a large volume of diffracting crystallites. The sample format is typically comprised of finely divided crystallites that are compacted into a flat plate; this format is amenable to a wide variety of materials. These factors serve to permit timely qualitative analyses which are requisite for many applications. Furthermore, with more advanced data analysis methods a wealth of additional information may be discerned. However, a drawback exists in the context of the para-focusing optics of laboratory diffractometers which produce patterns that display profiles of a most complex shape. While advanced data analysis methods can be used to model the various aberrations and account for the observed profile shape and position, there are a number of instrumental effects about which there is insufficient knowledge for reliable, a priori modeling of instrument performance. The task may be further compounded when instruments are set up incorrectly, as the resultant errors are convoluted into the already complex aberration set. Therefore, the results are often somewhat diabolical and the origin of difficulty is problematic to discern. The preferred method is to use National Institute of Standards and Technology, NIST, Standard Reference Materials, SRMs, to calibrate instruments in the field and qualify instrument performance. We describe the various methods wherein NIST SRMs may be used to discern sources of measurement error as well as properly characterize and calibrate instrument performance.
Modern Diffraction Methods
Wiley-VCH Verlag & Co. KGaA, Weinheim, -1
X-ray Powder Diffraction, Standard Reference Material, Rietveld Analysis, SI Traceability, Instrument Profile Function, fundamental parameters approach