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, pp. 195-197

Section 2.9.3.4. Cells specifically for neutrons

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. Cells specifically for neutrons

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2.9.3.4.1. Introduction

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The special characteristics of neutrons imply both advantages and challenges for the design of in situ experiments and their associated equipment. The differences in penetration depths between X-rays and neutrons and the correspondingly smaller scattering cross sections for neutrons, together with the much lower flux densities, imply that cells for neutrons are quite different from the miniature capillary cells for X-rays described in the previous sections. Above all, the sample volume is by necessity often much larger than the equivalent volume required for a laboratory X-ray or synchrotron experiment. However, the ability of neutrons to penetrate deep into sample environments has been of great importance for studying samples at very low temperature, under high pressure or within strong magnetic fields. Similarly, reaction cells for in situ investigations profit from the ability of neutrons to penetrate through thick-walled vessels, for example for studying gas–solid reactions under high pressure. Only relatively recently, with the availability of high-energy synchrotron beamlines (>100 keV), can X-rays effectively compete with neutrons in this domain. Even in these cases, the very different scattering properties of neutrons (e.g. the strong variation of cross section with isotope) means that some measurements that are challenging, if not impossible, with X-rays can become quite feasible with neutrons. The solid–gas reaction of intermetallic phases with H2 gas is a good example, where the positions of the interstitial H atoms can be located within a heavy-metal hydride (Kamazawa et al., 2013[link]). Similarly, the hydration of cement has been investigated many times, with improved time resolution resulting from developments in neutron optics and detector performance. In situ studies of oxidation reactions have also benefited from the better ability of neutrons to determine the atomic positions of oxygen during synthesis (Bianchini et al., 2013[link]). The investigation of chemical processes in the electrodes of batteries has, for example, been particularly fruitful. Once again, specialist cells for electrochemistry have been developed that take advantage of the penetration power of the neutrons in order to reveal bulk behaviour within the electrode material. Examples of these and other applications are given in an extensive review of in situ and time-resolved neutron scattering (Isnard, 2007[link]) and in the more recent articles by Hansen & Kohlmann (2014[link]), Sharma et al. (2015[link]) and Pang & Peterson (2015[link]). It should also be noted that different geometrical arrangements are used in angular-dispersive monochromatic neutron diffraction or when using a fixed-angle detector bank for time-of-flight neutron diffraction, which can have important implications for the cell design. In the following sections, we will examine some of these specialist cells in more detail.

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.

2.9.3.4.3. Electrochemistry using neutron diffraction

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The advantages of high penetration and sensitivity to light elements such as hydrogen, oxygen and lithium make neutron powder diffraction an interesting tool for investigating processes occurring within complex electrochemical systems. Lithium-ion batteries are one of the most widely used portable energy sources. These devices rely on the insertion of lithium ions into both positive and negative electrodes. A proper understanding of the structural processes that occur at the electrodes can only be obtained from in situ diffraction experiments performed during electrochemical charging and discharging. A suitable electrochemical cell for this type of measurement has been reported by Rosciano et al. (2008[link]). The challenge for the design of this type of cell is to enable the neutron-diffraction data to be collected with the minimum of hindrance, while allowing electrochemical characterization to be performed at the same time. In addition, the fact that most separators and polycarbonate-based electrolyte solutions contain large amounts of hydrogen presents problems due to the large incoherent neutron-scattering cross section of hydrogen, which results in a deterioration in the signal-to-background ratio. However, as pointed out by Sharma et al. (2011[link]), designs have been developed that minimize the amount of electrolyte required, and, where possible, deuterated solution can be used. Using a home-made design of a rollover, cylindrical cell that mimicked the geometry of commercial batteries, Sharma et al. (2011[link]) were able to probe structural changes in real time (5 min per pattern) as a function of electrochemical cycling using the Wombat powder diffractometer (ANSTO). Sharma et al. (2015[link]) have since reviewed both synchrotron and neutron electrochemistry cells. Pang & Peterson (2015[link]) provide an overview of all lithium-ion and sodium-ion battery materials studied by neutron powder diffraction in situ since 1998.

Battery materials and fuel cells are extensively used in a vast variety of applications in energy conversion and storage, and there is no doubt that in situ neutron powder diffraction will continue to play an important role in the efforts to further improve the performance of these materials. In Japan, for example, a new neutron-diffraction instrument (SPICA at the J-PARC spallation source) will be used to analyse atomic structures and the behaviour of batteries during their charge cycle. Both at spallation and reactor-based neutron sources, improvements in neutron optics and detector performance have reduced both the volume of sample needed for in situ experiments and the time required to collect each powder pattern.

2.9.3.4.4. Hydrothermal reaction cells

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Many materials with potential applications in technologically important fields can only be prepared by the supercritical hydrothermal synthesis method. A detailed knowledge of the reaction mechanisms is lacking, mainly because the processes take place within sealed and thick-walled reaction vessels. A technique is required that can penetrate the walls of the vessel during the reaction, and can reveal the kinetics and mechanism of bulk sample synthesis. Neutron diffraction is the ideal tool for this task. For example, Ok et al. (2010[link]) constructed a relatively simple chemical-reaction cell for investigating syntheses, even under extreme supercritical conditions, using of time-of-flight techniques. The cell itself was machined from a single ingot of Inconel, and had a maximum wall thickness of 4.0 mm. Thinner sections of 2.7 mm thickness were used in parts of the cell to reduce attenuation of the incident and scattered neutron beams. The vessel had a normal working pressure and temperature of 40 MPa at 723 K. The experiments were carried out on the POLARIS diffractometer at the ISIS pulsed spallation neutron source.

Another example of a hydrothermal reaction cell of somewhat different design is that used by Xia et al. (2010[link]). In this case, a large sample volume was chosen (320 ml internal volume) to allow bulk properties to be investigated. The cell had a dumbbell configuration, assembled from commercial stainless-steel components, that held most of the hydrothermal liquid, and a zero-scattering Ti–Zr alloy sample compartment with a 0.4 mm wall thickness. This choice of material and wall thickness for the sample cell dramatically reduced the background scattering from the container, but limited the operational range to temperatures up to 573 K and pressures up to 9 MPa. The cell was commissioned at the Wombat neutron powder diffractometer at ANSTO, using the in situ kinetic study of the hydrothermal phase transformations from leucite (KAlSi2O4) to analcime (NaAlSi2O6·H2O) as a demonstration of the capabilities of the equipment.

References

Bianchini, M., Leriche, J. B., Laborier, J.-L., Gendrin, L., Suard, E., Croguennec, L. & Masquelier, C. (2013). A new null matrix electrochemical cell for Rietveld refinements of in-situ or operando neutron powder diffraction data. J. Electrochem. Soc. 160, A2176–A2183.Google Scholar
Hansen, T. C. & Kohlmann, H. (2014). Chemical reactions followed by in situ neutron powder diffraction. Z. Anorg. Allg. Chem. 640, 3044–3063.Google Scholar
Isnard, O. (2007). A review of in situ and/or time resolved neutron scattering. C. R. Phys. 8, 789–805.Google Scholar
Kamazawa, K., Aoki, M., Noritake, T., Miwa, K., Sugiyama, J., Towata, S., Ishikiriyama, M., Callear, S. K., Jones, M. O. & David, W. I. F. (2013). In-operando neutron diffraction studies of transition metal hydrogen storage materials. Adv. Energ. Mater. 3, 39–42.Google Scholar
Ok, K. M., O'Hare, D., Smith, R. I., Chowdhury, M. & Fikremariam, H. (2010). New large volume hydrothermal reaction cell for studying chemical processes under supercritical hydrothermal conditions using time-resolved in situ neutron diffraction. Rev. Sci. Instrum. 81, 125107.Google Scholar
Pang, W. K. & Peterson, V. K. (2015). A custom battery for operando neutron powder diffraction studies of electrode structure. J. Appl. Cryst. 48, 280–290.Google Scholar
Rosciano, F., Holzapfel, M., Scheifele, W. & Novák, P. (2008). A novel electrochemical cell for in situ neutron diffraction studies of electrode materials for lithium-ion batteries. J. Appl. Cryst. 41, 690–694.Google Scholar
Sharma, N., Du, G., Studer, A. J., Guo, Z. & Peterson, V. K. (2011). In-situ neutron diffraction study of the MoS2 anode using a custom-built Li-ion battery. Solid State Ionics, 199–200, 37–43.Google Scholar
Sharma, N., Pang, W. K., Guo, Z. & Peterson, V. K. (2015). In situ powder diffraction studies of electrode materials in rechargeable batteries. ChemSusChem, 8, 2826–2853.Google Scholar
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
Xia, F., Qian, G., Brugger, J., Studer, A., Olsen, S. & Pring, A. (2010). A large volume cell for in situ neutron diffraction studies of hydrothermal crystallizations. Rev. Sci. Instrum. 81, 105107.Google Scholar








































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