International Tables for Crystallography

The optics and alignment of the divergent-beam laboratory X-ray powder diffractometer and its calibration using NIST standard reference materials
J. P. Cline, M. H. Mendenhall, D. Black, D. Windover and A. Henins. International Tables for Crystallography (2019). Vol. H, ch. 3.1, pp. 224-251  [ doi:10.1107/97809553602060000946 ]


The laboratory X-ray powder diffractometer is one of the primary analytical tools in materials science. It is applicable to nearly any crystalline material, and with advanced data-analysis methods, it can provide a wealth of information concerning sample character. Data from these machines, however, are beset by a complex aberration function that can be addressed through calibration with the use of NIST standard reference materials (SRMs). Laboratory diffractometers can be set up in a range of optical geometries; considered herein are those of Bragg–Brentano divergent-beam configuration using both incident- and diffracted-beam monochromators. We review the origin of the various aberrations affecting instruments of this geometry and the methods developed at NIST to align these machines in a first-principles context. Data-analysis methods are considered as being in two distinct categories: those that use empirical methods to parameterize the nature of the data for subsequent analysis, and those that use model functions to link the observation directly to a specific aspect of the experiment. We consider a multifaceted approach to instrument calibration using both the empirical and model-based data-analysis methods. The particular benefits of the fundamental-parameters approach are reviewed.

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About International Tables for Crystallography

International Tables for Crystallography is the definitive resource and reference work for crystallography. The series consists of nine volumes and comprises articles and tables of data relevant to crystallographic research and to applications of crystallographic methods in all sciences concerned with the structure and properties of materials.