We have designed and realized a temperature and pressure controlled cell for Neutron Reflectometry (NR) and Small Angle Neutron Scattering (SANS) that is compatible with simultaneous optical transmission and resistivity measurements. The cell can accommodate samples up to 102 mm (4 inch) in diameter, can be pressurized from vacuum up to 10 bar gas pressure and the sample temperature can be controlled up to 350°C. The four single crystal quartz windows ensure both a good neutron and optical transmission and hence can be used in combination with in-situ optical transmission measurements. We present the cell and illustrate its performance with a series of neutron reflectometry experiments performed on Ta based thin films under a hydrogen containing atmosphere.

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This paper studies the structural and optical properties of tantalum–iron-, tantalum–cobalt-, and tantalum–nickel-sputtered thin films both ex situ and while being exposed to various hydrogen pressures/concentrations, with a focus on optical hydrogen sensing applications. Optical hydrogen sensors require sensing materials that absorb hydrogen when exposed to a hydrogen-containing environment. In turn, the absorption of hydrogen causes a change in the optical properties that can be used to create a sensor. Here, we take tantalum as a starting material and alloy it with Fe, Co, or Ni with the aim to tune the optical hydrogen sensing properties. The rationale is that alloying with a smaller element would compress the unit cell, reduce the amount of hydrogen absorbed, and shift the pressure composition isotherm to higher pressures. X-ray diffraction shows that no lattice compression is realized for the crystalline Ta body-centered cubic phase when Ta is alloyed with Fe, Co, or Ni, but that phase segregation occurs where the crystalline body-centered cubic phase coexists with another phase, as for example an X-ray amorphous one or fine-grained intermetallic compounds. The fraction of this phase increases with increasing alloyant concentration up until the point that no more body-centered cubic phase is observed for 20% alloyant concentration. Neutron reflectometry indicates only a limited reduction of the hydrogen content with alloying. As such, the ability to tune the sensing performance of these materials by alloying with Fe, Co, and/or Ni is relatively small and less effective than substitution with previously studied Pd or Ru, which do allow for a tuning of the size of the unit cell, and consequently tunable hydrogen sensing properties. Despite this, optical transmission measurements show that a reversible, stable, and hysteresis-free optical response to hydrogen is achieved over a wide range of hydrogen pressures/concentrations for Ta–Fe, Ta–Co, or Ta–Ni alloys which would allow them to be used in optical hydrogen sensors@en

Lithium metal with its high theoretical capacity and low negative potential is considered one of the most important candidates to raise the energy density of all-solid-state batteries. However, lithium filament growth and its induced solid electrolyte decomposition pose severe challenges to realize a long cycle life. Here, dendrite growth in solid-state Li metal batteries is alleviated by introducing a high dielectric material, barium titanate, as a filler that removes the electric field gradients that catalyze dendrite formation. In symmetrical Li-metal cells, this results in a very small over-potential of only 48 mV at a relatively high current density of 1 mA cm⁻², when cycling a capacity of 2 mA h cm⁻² during 1700 h. The high dielectric filler improves the Coulombic efficiency and cycle life of full cells and suppresses electrolyte decomposition as indicated by solid-state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) measurements. This indicates that the high dielectric filler can suppress dendrite formation, thereby reducing solid electrolyte decomposition reactions, resulting in the observed low overpotentials and improved cycling efficiency.

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Here, we study the structural and optical properties of tetragonal β-tantalum-sputtered thin films both ex situ and when exposed to hydrogen, with a focus on optical hydrogen sensing applications. Using optical transmission measurements, out-of-plane and in-plane X-ray diffraction, and X-ray and neutron reflectometry, we show that thin film β-tantalum gradually, reversibly, and hysteresis-freely absorbs hydrogen with an increasing hydrogen pressure/concentration. The gradual absorption of hydrogen with increasing hydrogen concentrations induces a change in the optical transmission and reflection. These quantities change reversibly and are hysteresis-free over at least 5 orders of magnitude in hydrogen pressure/concentration, making β-tantalum a suitable hydrogen sensing material. At all partial hydrogen pressures studied, we observe that the volumetric expansion, hydrogen-to-metal ratio, and lattice expansion are substantially smaller than for body-centered cubic α-tantalum.

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The thermodynamic and thermo-physical properties of the molten salt system [Formula presented] have been investigated using an experimental and modelling approach. This molten salt system includes a single intermediate compound [Formula presented], whose structure has been investigated using X-ray and neutron diffraction. Furthermore, this system exhibits solubility of [Formula presented] in [Formula presented] at high temperatures up to a concentration of around 25% [Formula presented] at 1060 K. Additionally, our measurements show solubility of [Formula presented] in [Formula presented] up to about 5% [Formula presented] at 973 K. The investigation of these solid solutions has been performed using quenching experiments and subsequent post-characterisation by X-ray diffraction (XRD). Phase diagram equilibria have also been investigated using differential scanning calorimetry (DSC). Using the aforementioned information on phase transitions, intermediate compound formation, and mutual solid solubility, a thermodynamic assessment of the system has been performed using the CALPHAD method. The model for the Gibbs energy of the liquid solution is the quasi-chemical formalism in the quadruplet approximation, while the model for the Gibbs energy of the solid solutions is a two-sublattice polynomial model.

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The quaternary compound Cs₂Pb(MoO₄)₂ was synthesized and its structure was characterized using X-ray and neutron diffraction from 298 to 773 K, while thermal expansion was studied from 298 to 723 K. The crystal structure of the high-temperature phase β-Cs₂Pb(MoO₄)₂ was elucidated, and it was found to crystallize in the space group R3̅m (No. 166), i.e., with a palmierite structure. In addition, the oxidation state of Mo in the low-temperature phase α-Cs₂Pb(MoO₄)₂ was studied using X-ray absorption near-edge structure spectroscopy. Phase diagram equilibrium measurements in the Cs₂MoO₄-PbMoO₄ system were performed, revisiting a previously reported phase diagram. The equilibrium phase diagram proposed here includes a different composition of the intermediate compound in this system. The obtained data can serve as relevant information for thermodynamic modeling in view of the safety assessment of next-generation lead-cooled fast reactors.

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The horizontal time-of-flight neutron reflectometer at the reactor of the Delft University of Technology, The Netherlands, has been completely renewed, relocated, and upgraded and allows for the study of air/liquid, solid/liquid, and solid/air interfaces. Innovations in the redesign include (i) a completely flexible double disk chopper system allowing to choose the optimal wavelength resolution with exchangeable neutron guide sections between the chopper disks to increase intensity, (ii) a movable second diaphragm just before the sample position to better control the beam footprint on the sample and effectively decrease counting times, and (iii) guides along the entire flight path of the neutron reflectometer. The performance of the renewed reflectometer is illustrated with measurements of hydrogen sensing materials.

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A newly developed Boron-based Large-scale Observation of Soil Moisture (or BLOSM) system is currently being tested and implemented. The stationary system provides a cost-effective way to measure fast and thermalized neutrons by using low-cost, non–hazardous and accessible materials and equipment. BLOSM operates by measuring cosmic-ray induced neutrons and by comparing the amount of fast neutrons with the amount of thermal neutrons. Fast neutrons are moderated by hydrogen atoms in the air, organic materials, and especially and primarily by water in the soil, causing the ratio between fast and thermal to be a strong indicator of soil moisture content. The fast/thermal ratio is representative for soil moisture a scale of about 30 hectares, while standard soil moisture measurements are representative for less than a square meter. This is a well-established fact but present neutron detectors are very costly. Thanks to the low-cost of the probe, BLOSM can eventually be applied at a large scale and significantly increase the number of soil–water data points thereby enabling improvement of existing hydrology models as well as new applications such as monitoring fire hazards and agricultural droughts. Here, we present the build and first tests in the laboratory. We show that BLOSM can indeed measure fast and thermal neutrons, which opens the way to applications outside the laboratory.

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Li₃YX₆(X = Cl, Br) materials are Li-ion conductors that can be used as solid electrolytes in all solid-state batteries. Solid electrolytes ideally have high ionic conductivity and (electro)chemical compatibility with the electrodes. It was proven that introducing Br to Li₃YCl₆increases ionic conductivity but, according to thermodynamic calculations, should also reduce oxidative stability. In this paper, the trade-off between ionic conductivity and electrochemical stability in Li₃YBr_xCl_6-xhalogen-substituted compounds is investigated. The compositions of Li₃YBr_1.5Cl_4.5and Li₃YBr_4.5Cl_1.5are reported for the first time, along with a consistent analysis of the whole Li₃YBr_xCl_6-x(x = 0-6) tie-line. The results show that, while Br-rich materials are more conductive (5.36 × 10^-3S/cm at 30 °C for x = 4.5), the oxidative stability is lower (∼ 3 V compared to ∼ 3.5 V). Small Br content (x = 1.5) does not affect oxidative stability but substantially increases ionic conductivity compared to pristine Li₃YCl₆(2.1 compared to 0.049 × 10^-3S/cm at 30 °C). This work highlights that optimization of substitutions in the anion framework provide prolific and rational avenues for tailoring the properties of solid electrolytes.

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Li metal batteries are being intensively investigated as a means to achieve higher energy density when compared with standard Li-ion batteries. However, the formation of dendritic and mossy Li metal microstructures at the negative electrode during stripping/plating cycles causes electrolyte decomposition and the formation of electronically disconnected Li metal particles. Here we investigate the use of a Cu current collector coated with a high dielectric BaTiO₃ porous scaffold to suppress the electrical field gradients that cause morphological inhomogeneities during Li metal stripping/plating. Applying operando solid-state nuclear magnetic resonance measurements, we demonstrate that the high dielectric BaTiO₃ porous scaffold promotes dense Li deposition, improves the average plating/stripping efficiency and extends the cycling life of the cell compared to both bare Cu and to a low dielectric scaffold material (i.e., Al₂O₃). We report electrochemical tests in full anode-free coin cells using a LiNi_0.8Co_0.1Mn_0.1O₂-based positive electrode and a LiPF₆-based electrolyte to demonstrate the cycling efficiency of the BaTiO₃-coated Cu electrode.

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Iron is a promising, earth-abundant material for future energy applications. In this study, we use a neutron diffractometer to investigate the properties of an iron electrode in an alkaline environment. As neutrons penetrate deeply into materials, neutron scattering gives us a unique insight into what is happening inside the electrode. We made our measurements while the electrode was charging or discharging. Our key questions are: Which phases occur for the first and second discharge plateaus? And why are iron electrodes less responsive at higher discharge rates? We conclude that metallic iron and iron hydroxide form the redox pair for the first discharge plateau. For the second discharge plateau, we found a phase similar to feroxyhyte but with symmetrical and equally spaced arrangement of hydrogen atoms. The data suggest that no other iron oxide or iron (oxy)hydroxide formed. Remarkable findings include the following: (1) substantial amounts of iron hydroxide are always present inside the electrode. (2) Passivation is mostly caused by iron hydroxide that is unable to recharge. (3) Iron fractions change as expected, while iron hydroxide fractions are delayed, resulting in substantial amounts of
amorphous, undetectable iron phases. About 40% of the participating iron of the first plateau and about 55% of the participating iron for the second plateau are undetectable. (4) Massive and unexpected precipitation of iron hydroxide occurs in the transition from discharging to charging. (2), (3), and (4) together cause accumulation of iron hydroxide inside the electrode.@en

We have recently shown how a polarized beam in Talbot-Lau interferometric imaging can be used to analyze strong magnetic fields through the spin dependent differential phase effect at field gradients. While in that case an adiabatic spin coupling with the sample field is required, here we investigate a nonadiabatic coupling causing a spatial splitting of the neutron spin states with respect to the external magnetic field. This subsequently leads to no phase contrast signal but a loss of interferometer visibility referred to as dark-field contrast. We demonstrate how the implementation of spin analysis to the Talbot-Lau interferometer setup enables one to recover the differential phase induced to a single spin state. Thus, we show that the dark-field contrast is a measure of the quantum mechanical spin split analogous to the Stern-Gerlach experiment without, however, spatial beam separation. In addition, the spin analyzed dark-field contrast imaging introduced here bears the potential to probe polarization dependent small-angle scattering and thus magnetic microstructures.

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The initial formation stages of surfactant-templated silica thin films which grow at the air-water interface were studied using combined spin-echo modulated small-angle neutron scattering (SEMSANS) and small-angle neutron scattering (SANS). The films are formed from either a cationic surfactant or nonionic surfactant (C16EO8) in a dilute acidic solution by the addition of tetramethoxysilane. Previous work has suggested a two stage formation mechanism with mesostructured particle formation in the bulk solution driving film formation at the solution surface. From the SEMSANS data, it is possible to pinpoint accurately the time associated with the formation of large particles in solution that go on to form the film and to show their emergence is concomitant with the appearance of Bragg peaks in the SANS pattern, associated with the two-dimensional hexagonal order. The combination of SANS and SEMSANS allows a complete depiction of the steps of the synthesis that occur in the subphase.

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Lithium halide electrolytes with high ion conductivity and good cathode compatibility have shown great potential for solid-state batteries. Li₃YBr₆, with a conductivity of 0.39 mS/cm at room temperature, synthesized by mechanical milling (BM-Li₃YBr₆), which can be further increased by heat treatment. The annealing parameters are tailored to obtain pure Li₃YBr₆ (AN-Li₃YBr₆) with a higher conductivity of 3.31 mS/cm by annealing the BM-Li₃YBr₆ at 500 °C for 5 h. The higher conductivity of AN-Li₃YBr₆ compared to the previously-reported results is due to the lower activation energy. NMR and simulation results show that the lithium ion migration between Li-1 and Li-2 sites along the [001] direction is the major obstacle for lithium diffusion in AN-Li₃YBr₆. The K- and L₃-edge X-ray absorption near-edge structure (XANES) of Y for BM-Li₃YBr₆ and AN-Li₃YBr₆ showed that Y exists with similar local structures. The increased vibrations of AN-Li₃YBr₆ due to increased temperatures increase the rate of lithium jumping from one site to another, yielding higher lithium ion mobility. Lithium nuclear density maps prove that the mobile lithium on the 4g(Li) site is more sensitive to the varying temperatures. Both BM- and AN-Li₃YBr₆ are incompatible with Li, however, an annealing process can improve the electrochemical stability. Both the experimental and simulation results confirm the anode incompatibility between In and AN-Li₃YBr₆. To mitigate the cathode and anode incompatibility with AN-Li₃YBr₆, a LiNbO₃ coating layer and a Li_5.7PS_4.7Cl_1.3 buffer layer are introduced at the cathode side and anode side, respectively, to assemble all-solid-state batteries with improved capacity and cyclability.

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A time-of-flight modulation of intensity by zero effort spectrometer mode has been developed for the Larmor instrument at the ISIS pulsed neutron source. The instrument utilizes resonant spin flippers that employ electromagnets with pole shoes, allowing the flippers to operate at frequencies up to 3 MHz. Tests were conducted at modulation frequencies of 103 kHz, 413 kHz, 826 kHz, and 1.03 MHz, resulting in a Fourier time range of ∼0.1 ns to 30 ns using a wavelength band of 4 Å-11 Å.

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A time of flight MIEZE spectrometerstudyis presented. The instrumentuses solenoid radio frequency(RF)spin flipperswithsquare pole shoes and a magnetic yoke. These flippers can achieve higherstaticfields than conventional resonant RF spin flippers, which employ an air core.High fields are crucial for the construction of a high resolution and compact MIEZE spectrometer.Using both types of flipperstwo MIEZE spectrometer configurationsare constructed and comparedon the same beam line. It was demonstratedthat the pole shoe/solenoid coil RF flipperscan achieve a MIEZE signal, which is similarin quality to theconventionalreferencesetup.The highest obtained modulation frequency was 100kHz.@en