Neutron scattering opens up window on novel materials
Neutron sources have an important role to play in the development of new materials for storing sustainable energy, allowing researchers to gain deeper insights into their functionality. We spoke to Professor Elizabeth Blackburn about how she and her team are using neutron scattering techniques to investigate energy and quantum materials.
The properties of a material may not always be fully evident from surface analysis, as the internal structure often has a major influence on how it functions. Neutron sources play an important role in this respect, enabling researchers to study the interaction between neutrons and different materials in scattering experiments, from which deeper insights can then be drawn. “Neutrons interact with the nuclei of atoms, rather than the electrons around them. Neutrons therefore scatter in a different way to x-rays from a synchrotron, so that sometimes you can see different phenomena more clearly,” explains Elizabeth Blackburn, Professor in the Department of Physics at Lund University in Sweden.
As the Principal Investigator of a project backed by the Swedish Research Council (Vetenskapsrådet), Professor Blackburn is part of a team of researchers using neutron scattering techniques to investigate the potential of certain materials in energy storage, a topic central to the wider goal of moving towards a more sustainable society. One of the main advantages of neutrons in this respect is that the particle has a magnetic moment in and of itself. “We can use the magnetic moment of the neutron to interact directly with magnetic fields, including those from nuclei like hydrogen,” says Professor Blackburn. “We’ve been conducting experiments on the motion of lithium deep inside some materials that could be used as lithium batteries. We’re also investigating quantum materials, which are essentially materials in which quantum mechanics is necessary to explain their fundamental behaviour. This typically means that electrons show strange magnetic effects. With wide angle scattering techniques, we are able to look at energy materials right down to the atomic scale, and build a fuller picture of their functionality.”
Polarised neutrons
This research involves using what are called polarised neutrons, where the neutrons in a beam are aligned, with their dipoles pointing in the same direction. There are several different ways of aligning neutrons; researchers at Lund
have now developed a polarising supermirror for this purpose. “A polarising supermirror can be thought of as a bit like an optical fibre. If you put neutrons in at the beginning of a waveguide coated with these supermirrors, you get most of the neutrons at the end. So you hardly lose any, however far you transmit them. If you choose the right material, the supermirror will absorb all of the neutrons that have the polarisation direction that you don’t want, and only keep the ones that are aligned in the way that you do,” says Professor Blackburn. These polarising supermirrors
are a fairly well established concept, but now Professor Blackburn and her team have developed a novel design. “We have a kind of array of these supermirrors with a particular shape, a logarithmic spiral. We have designed and tested this with various simulations, and a device has been constructed to our specifications,” she outlines.
The plan is to test this device at the ISIS neutron and muon source in the UK later this year, the results of which can then inform the design of another for use on an extreme environment spectrometer at the European
Spallation Source (ESS) called BIFROST. The ESS is still under construction at Lund, but when finished it promises to open up new investigative opportunities for researchers across a wide variety of disciplines, and the polarising supermirrors will be an important component. “They will be available for use at both ISIS and the ESS by whoever wants to use them,” says Professor Blackburn. As an experimentalist, Professor Blackburn is herself keen to make full use of these kinds of instruments, which she says can play a highly valuable role in research. “For example, people studying the motion of hydrogen – in water or in materials that absorb a lot of hydrogen –
collaboration with a researcher at ISIS. This work has been progressing well,” she outlines. On the quantum materials side, attention in the project has largely focused on the magnetoelectric effect, where an electric field can be used to reflect magnetism and viceversa. “We have been conducting detailed experiments at the ISIS facility, and this work has also been going well. However, it’s very complex, and it’s taking us some time to unravel what’s going on,” continues Professor Blackburn. “This side of the project is slightly more exploratory, in that we are trying to find new types of behaviour that haven’t really been observed before.”
“We’re investigating quantum materials, essentially materials in which quantum mechanics is necessary to explain the fundamental behaviour. This typically means that electrons show strange magnetic effects.”
have found that one of the best ways to analyse the data is to use polarised neutrons,” she explains. “The polarisation capability gives you a greater degree of certainty when analysing the contributions from hydrogen. Certain materials can absorb a lot of hydrogen.” These materials can be very porous, and the behaviour by which hydrogen is absorbed in the interior may be very different to that seen at the surface. A neutron source helps researchers look at what’s happening deep within a material, and Professor Blackburn is using neutron scattering to build a fuller picture in this respect. “On the energy materials side, we’ve been looking at the motion of lithium in two compounds, for which we developed simulation tools in
Instruments
The instrumentation side of the project is also well advanced, with plans to test the polarising supermirror in the next few months, in good time to build a second one to be used at the ESS. The aim is to provide a polarisation capability to instruments at ISIS and ESS, which will benefit not just researchers in physics or nanoscience, but also scientists from a wide range of other fields.
“The instrumentation we are building will aid in the development of magnetic materials that will eventually be used in making better transformers. These instruments will also be of use to people looking at polymer dynamics for example, or in studying the behaviour of cell membranes,” says Professor Blackburn.
WIdE-aNglE NEuTroN PolarIsaTIoN aNalysIs To sTudy ENErgy aNd quaNTum maTErIals
Project objectives
To provide Europe’s neutron facilities with new, powerful polarisation analysis hardware, covering wide angles to get as much data as possible out of the neutron instruments. To resolve hard materials questions using this equipment, with a focus on energy and quantum materials.
Project Funding
This project was funded by the Swedish Research Council. The total amount of funding was 15,700,000 SEK.
Project Partners
• KTH: Martin Månsson
• European Spallation Source: Wai-Tung (Hal) Lee, Pascale Deen, Rasmus Toft-Petersen
• ISIS Neutron and Muon Source: GØran Nilsen, Pascal Manuel
Contact details
Project Coordinator, Professor Elizabeth Blackburn Synchrotron Radiation Research Lund University Box 118, Lund Sweden
T: +46 46 2227152
E: elizabeth.blackburn@sljus.lu.se
W: https://portal.research.lu.se/en/persons/ elizabeth-blackburn
W: http://www.sljus.lu.se/research-fields/ magnetism-and-superconductivity/
https://doi.org/10.1051/epjconf/202328603004, https://doi.org/10.1051/epjconf/202328606002
Blackburn is a Professor of Physics at Lund University a position she has held since 2018. She gained her degree at the University of Cambridge, and has worked in research at institutions in Europe and America. In her role at Lund she has helped to develop a hub of research activity on magnetic materials and the interesting physics brought about by the behaviour of electrons in solids.
