6. November 2018

Linking Structure to Dynamics in Protic Ionic Liquids: A Neutron Scattering Study of Correlated and Single-Particle Motions

T. Burankova et al., Scientific Reports 8, 16400 (2018). Coupling between dynamical heterogeneity of ionic liquids and their structural periodicity on different length-scales can be directly probed by quasielastic neutron scattering with polarization analysis. The technique provides the tools to investigate single-particle and cooperative ion motions separately and, thus, dynamics of ion associations affecting the net charge transport can be experimentally explored. The focus of this study is the structure-dynamic relationship in the protic ionic liquid, triethylammonium triflate, characterized by strong hydrogen bonds between cations and anions. The site-selective deuterium/hydrogen-isotope substitution was applied to modulate the relative contributions of different atom groups to the total coherent and incoherent scattering signal. This approach in combination with molecular dynamics simulations allowed us to obtain a sophisticated description of cation self-diffusion and confined ion pair dynamics from the incoherent spectral component by using the acidic proton as a tagged particle. The coherent contribution of the neutron spectra demonstrated substantial ion association leading to collective ion migration that preserves charge alteration on picosecond time scale, as well as correlation of the localized dynamics occurring between adjacent ions.

25. October 2018

Dynamic volume magnetic domain wall imaging in grain oriented electrical steel at power frequencies with accumulative high-frame rate neutron dark-field imaging

R. Harti et al., Scientific Reports 8, 15754 (2018). The mobility of magnetic domains forms the link between the basic physical properties of a magnetic material and its global characteristics such as permeability and saturation field. Most commonly, surface domain structure are studied using magneto-optical Kerr microscopy. The limited information depth of approx. 20 nanometers, however, allows only for an indirect interpretation of the internal volume domain structures. Here we show how accumulative high-frame rate dynamic neutron dark-field imaging is able for the first time to visualize the dynamic of the volume magnetic domain structures in grain oriented electrical steel laminations at power frequencies. In particular we studied the volume domain structures with a spatial resolution of ∼100 μm and successfully quantified domain sizes, wall velocities, domain annihilation and its duration and domain wall multiplication in real time recordings at power frequencies of 10, 25 and 50 Hz with ±262.5 A/m and ±525 A/m (peak to peak) applied field.

24. October 2018

Dynamics of the Coordination Complexes in a Solid-State Mg Electrolyte

T. Burankova et al., Journal of Physical Chemistry Letters 9, 6450 (2018). Coordination complexes of magnesium borohydride show promising properties as solid electrolytes for magnesium ion batteries and warrant a thorough microscopic description of factors governing their mobility properties. Here, the dynamics of Mg(BH₄)₂-diglyme_0.5 on the atomic level are investigated by means of quasielastic neutron scattering supported by density functional theory calculations and IR and NMR spectroscopy. Employing deuterium labeling, we can unambiguously separate all the hydrogen-containing electrolyte components, which facilitate Mg²⁺ transport, and provide a detailed analytical description of their motions on the picosecond time scale. The planar diglyme chain coordinating the central Mg atom appears to be flexible, while two dynamically different groups of [BH₄]⁻ anions undergo reorientations. The latter has important implications for the thermal stability and conductivity of Mg(BH₄)₂-diglyme_0.5 and demonstrates that the presence of excess Mg(BH₄)₂ units in partially chelated Mg complexes may improve the overall performance of related solid-state electrolytes.

22. October 2018

Multiple Coulomb phase in the fluoride pyrochlore CsNiCrF₆

T. Fennell et al., Nature Physics, adv. online publication (2018). The Coulomb phase is an idealized state of matter whose properties are determined by factors beyond conventional consid- erations of symmetry, including global topology, conservation laws and emergent order. Theoretically, Coulomb phases occur in ice-type systems such as water ice and spin ice; in dimer models; and in certain spin liquids. However, apart from ice-type systems, more general experimental examples are very scarce. Here we study the partly disordered material CsNiCrF₆ and show that this material is a multiple Coulomb phase with signature correlations in three degrees of freedom: charge configurations, atom displacements and spin configurations. We use neutron and X-ray scattering to separate these correlations and to deter- mine the magnetic excitation spectrum. Our results show how the structural and magnetic properties of apparently disordered materials may inherit, and be dictated by, a hidden symmetry—the local gauge symmetry of an underlying Coulomb phase.

7. September 2018

ISNR honorary membership awarded to Eberhard Lehmann

The International Society for Neutron Radiology ISNR was founded in 1996 with the aim of organizing regular conferences focusing on the use of neutrons for imaging purposes. During the 11th World Conference on Neutron Radiography, held recently in Sydney (Australia) and organized by ANSTO, the Honorary Membership of ISNR was awarded to Eberhard Lehmann - in recognition of his contributions for the progress in the field of neutron imaging on national and international level. The Neutron Imaging and Activation Group NIAG of the LNS has been active member in ISNR from the very beginning. Presently and since 2014, Markus Strobl the head of NIAG is vice-president elected of ISNR – and was recently reelected until 2022. In addition, NIAG member Pavel Trtik is now representing PSI in the ISNR board until 2022.