International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 2.9, p. 196

Section 2.9.3.4.2. Solid–gas reactions

W. van Beeka* and P. Pattisona,b

aSwiss–Norwegian Beamlines at ESRF, CS 40220, 38043 Grenoble CEDEX 9, France, and bLaboratory for Quantum Magnetism, Institute of Physics, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland
Correspondence e-mail:  wouter@esrf.fr

2.9.3.4.2. Solid–gas reactions

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Suitable storage media for hydrogen and other small molecules include hydrides, hydrates, clathrates and other microporous materials [e.g. metal-organic frameworks (MOFs)]. In situ neutron powder diffraction has been the method of choice to investigate solid–gas reactions involving light molecules reacting with these types of framework structures, and a wide variety of in situ cells have been developed for this purpose. The design of the cell can be quite primitive, yet still be very successful for this kind of application. As a simple example, we consider the study of the reduction of a perovskite-related oxide under flowing hydrogen carried out at D20 at the Institut Laue–Langevin (ILL) in Grenoble (Tonus et al., 2009[link]). The powder sample was loaded into a quartz tube (12 mm diameter) and mounted in the standard D20 furnace. The tube was connected to a flow of reducing gas controlled by a needle valve. High-quality data could be collected in a short time (a few minutes) at high temperature under flowing H2 gas, in this case up to a maximum temperature of 973 K. Occupancy factors for the different oxygen sites could be refined as a function of temperature under reducing and oxidizing conditions.

In another example, the goal was to investigate solid–gas reactions under pressures of 16 MPa and temperatures up to 673 K (Widenmeyer et al., 2013[link]). Since the use of thin-walled single-crystal sapphire capillaries has become routine in synchrotron powder X-ray diffraction, the authors decided to adopt a similar strategy for the neutron-diffraction experiment. In this case, they selected a 6 mm diameter sapphire tube with steel end caps and metal seals. Pressures of 16 MPa could be achieved over periods of days without measurable pressure loss, and the powder data were of high quality, allowing Rietveld refinement of crystal structures including light-atom positions, displacement parameters and site occupancies. In addition to providing good-quality data and a low background, the sapphire tube also has the advantage of being chemically very robust and hence avoiding, for example, the problem of hydrogen embrittle­ment.

References

Tonus, F., Bahout, M., Henry, P. F., Dutton, S. E., Roisnel, T. & Battle, P. D. (2009). Use of in situ neutron diffraction to monitor high-temperature, solid/H2-gas reactions. Chem. Commun. pp. 2556–2558.Google Scholar
Widenmeyer, M., Niewa, R., Hansen, T. C. & Kohlmann, H. (2013). In situ neutron diffraction as a probe on formation and decomposition of nitrides and hydrides: a case study. Z. Anorg. Allg. Chem. 639, 285–295.Google Scholar








































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