Low‐temperature powder X‐ray diffraction measurements in vacuum: analysis of the thermal displacement of copper. (21st January 2016)

• Record Type: Journal Article
• Authors: Wahlberg, Nanna; Bindzus, Niels; Christensen, Sebastian; Becker, Jacob; Dippel, Ann-Christin; Jørgensen, Mads Ry Vogel; Iversen, Bo Brummerstedt
• Is Part Of: Journal of applied crystallography. Volume 49:Part 1(2016:Feb.)
• Page Start: 110
• Page End: 119
• Publication Date: 2016-01-21
• Subjects: synchrotron powder X‐ray diffraction -- in‐vacuum cooling -- anharmonicity -- electron density -- copper; Crystallography -- Periodicals; 548.05
• DOI: 10.1107/S1600576715022621
• Languages: English
• ISSNs: 0021-8898

Abstract

Abstract : A cooling system compatible with in‐vacuum operation is reported. The temperature has been calibrated by comparison of the unit‐cell and thermal displacement parameters of copper. Furthermore, the high‐quality diffraction data of copper allowed a detailed modelling of the electron density and the anharmonic atomic displacement. Abstract : A serious limitation of the all‐in‐vacuum diffractometer reported by Straasø, Dippel, Becker & Als‐Nielsen [ J. Synchrotron Rad. (2014), 21, 119–126] has so far been the inability to cool samples to near‐cryogenic temperatures during measurement. The problem is solved by placing the sample in a jet of helium gas cooled by liquid nitrogen. The resulting temperature change is quantified by determining the change in unit‐cell parameter and atomic displacement parameter of copper. The cooling proved successful, with a resulting temperature of ∼95 (3) K. The measured powder X‐ray diffraction data are of superb quality and high resolution [up to sinθ/λ = 2.2 Å −1 ], permitting an extensive modelling of the thermal displacement. The anharmonic displacement of copper was modelled by a Gram–Charlier expansion of the temperature factor. As expected, the corresponding probability distribution function shows an increased probability away from neighbouring atoms and a decreased probability towards them.