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Standard Reference Material (SRM 1990) for Single Crystal Diffractometer Alignment

Published

Author(s)

Winnie K. Wong-Ng, T Siegrist, G DeTitta, L Finger, H Evans, E Gabe, G Enright, J T. Armstrong, M Levenson, Lawrence P. Cook, C R. Hubbard

Abstract

Through extensive international collaborations, a standard reference material, SRM 1990 (a set of 3500 units of Cr-doped Al2O3, or ruby sphere) for single crystal diffractometer alignment has been certified at NIST after a successful international round-robin . The round-robin project was launched by distributing 50 sets of ruby spheres and zeolite reference crystals from Woodward-Hauptman Medical Research Center, along with an instruction manual to various laboratories. The results of the round robin project confirmed that well-aligned diffractometers are important for obtaining accurate lattice parameters, and that the ruby spheres satisfy the criteria required of a standard reference material. During the lattice parameters certification process, a total of 39 ruby spheres were measured using four single crystal diffractometers. These rubies are rhombohedral, with space group Rc. The certified mean unit cell parameters are a = 4.76080 0.00029 (expanded uncertainties), and c = 12.99568 0.00087 . Five samples of powdered rubies were measured on a Guinier-H gg transmission camera, giving good agreement with the values obtained from the single crystal spheres (a = 4.76093 0.00031 , and c = 12.9959 0.0023 ). The chromium composition was found to be relatively homogenous (0.42 0.011 mole %, expanded uncertainty). Various systematic errors associated with diffractometer alignment were also investigated. Among them, thermal expansion and refraction corrections were applied. The auxiliary data on the chromium content will also be useful for microanalytical calibrations.
Citation
Journal of Research (NIST JRES) -
Volume
106 No. 6

Keywords

alignment standard, Cr-content, international round robin, NIST SRM 1990, ruby spheres, single crystal x-ray diffractometers

Citation

Wong-Ng, W. , Siegrist, T. , DeTitta, G. , Finger, L. , Evans, H. , Gabe, E. , Enright, G. , Armstrong, J. , Levenson, M. , Cook, L. and Hubbard, C. (2001), Standard Reference Material (SRM 1990) for Single Crystal Diffractometer Alignment, Journal of Research (NIST JRES), National Institute of Standards and Technology, Gaithersburg, MD (Accessed May 23, 2024)

Issues

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Created November 1, 2001, Updated February 19, 2017