title: Standard Reference Material (SRM 1990) For Single Crystal Diffractometer Alignment.
abstract: An international project was successfully completed which involved two major undertakings: (1) a round-robin to demonstrate the viability of the selected standard and (2) the certification of the lattice parameters of the SRM 1990, a Standard Reference Material(®) for single crystal diffractometer alignment. This SRM is a set of ≈3500 units of Cr-doped Al2O3, or ruby spheres [(0.420.011 mole fraction % Cr (expanded uncertainty)]. The round-robin consisted of determination of lattice parameters of a pair of crystals: the ruby sphere as a standard, and a zeolite reference to serve as an unknown. Fifty pairs of crystals were dispatched from Hauptman-Woodward Medical Research Institute to volunteers in x-ray laboratories world-wide. A total of 45 sets of data was received from 32 laboratories. The mean unit cell parameters of the ruby spheres was found to be a=4.7608 Å±0.0062 Å, and c=12.9979 Å±0.020 Å (95 % intervals of the laboratory means). The source of errors of outlier data was identified. The SRM project involved the certification of lattice parameters using four well-aligned single crystal diffractometers at (Bell Laboratories) Lucent Technologies and at NRC of Canada (39 ruby spheres), the quantification of the Cr content using a combined microprobe and SEM/EDS technique, and the evaluation of the mosaicity of the ruby spheres using a double-crystal spectrometry method. A confirmation of the lattice parameters was also conducted using a Guinier-Hägg camera. Systematic corrections of thermal expansion and refraction corrections were applied. These rubies- are rhombohedral, with space group [Formula: see text]. The certified mean unit cell parameters are a=4.76080±0.00029 Å, and c=12.99568 Å±0.00087 Å (expanded uncertainty). These certified lattice parameters fall well within the results of those obtained from the international round-robin study. The Guinier-Hägg transmission measurements on five samples of powdered rubies (a=4.7610 Å±0.0013 Å, and c = 12.9954 Å±0.0034 Å) agreed well with the values obtained from the single crystal spheres.
authors: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors: W
authors: W
authors: Wong-Ng
authors: Inorganic 2, Lund University, Sweden.
authors: T
authors: T
authors: Siegrist
authors: Hauptman-Woodward Medical Research Institute, Buffalo, NY 14203.
authors: G T
authors: GT
authors: DeTitta
authors: Geophysical Laboratory, Washington, DC 20015.
authors: L W
authors: LW
authors: Finger
authors: U.S. Geological Survey,, Reston, VA 22092.
authors: H T
authors: HT
authors: Evans
authors: Steacie Institute for Molecular Sciences, NRC, Ottawa, Canada K1A 0R6.
authors: E J
authors: EJ
authors: Gabe
authors: Steacie Institute for Molecular Sciences, NRC, Ottawa, Canada K1A 0R6.
authors: G D
authors: GD
authors: Enright
authors: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors: J T
authors: JT
authors: Armstrong
authors: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors: M
authors: M
authors: Levenson
authors: National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
authors: L P
authors: LP
authors: Cook
authors: Oak Ridge National Laboratory, Oak Ridge, TN 37831.
authors: C R
authors: CR
authors: Hubbard
keywords: Cr-content; NIST SRM 1990; alignment standard; international round robin; ruby spheres; single crystal x-ray diffractometers