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10 years ago, Dave Mao, director of EFree (energy frontier research in extreme environments), a DOE energy frontier recognized the importance of neutron science for energy research. The subsequent establishment of a neutron group within EFree lead to the establishment of an “Instrument Development Team” for SNAP, the High-Pressure beamline at the Spallation Neutron Source at Oak Ridge National Laboratory in Tennessee. The idea was to develop novel high pressure techniques to expand the pressure range for neutron diffraction. A goal was set to reach half megabar levels (50 GPa), which at the time was considered as extremely challenging. Heremore » we will give a brief overview of the developments during the last decade in this novel area of research. Fortunately, during this period multi carat diamond anvils have become available mainly by the chemical vapor deposition process (CVD), making research in this pressure range and beyond rather routine. This paper shows the latest developments in large anvil designs, compact multiple ton diamond cells and some examples of high-quality neutron diffraction patterns of sample sizes far below conventional levels.« less

From crystalline tetrahydrofuran clathrate hydrate, THF–CH (THF·17H₂O, cubic structure II), three distinct polyamorphs can be derived. First, THF–CH undergoes pressure-induced amorphization when pressurized to 1.3 GPa in the temperature range 77–140 K to a form which, in analogy to pure ice, may be called high-density amorphous (HDA). Second, HDA can be converted to a densified form, VHDA, upon heat-cycling at 1.8 GPa to 180 K. Decompression of VHDA to atmospheric pressure below 130 K produces the third form, recovered amorphous (RA). Results from neutron scattering experiments and molecular dynamics simulations provide a generalized picture of the structure of amorphous THFmore » hydrates with respect to crystalline THF–CH and liquid THF·17H₂O solution (~2.5 M). Although fully amorphous, HDA is heterogeneous with two length scales for water–water correlations (less dense local water structure) and guest–water correlations (denser THF hydration structure). The hydration structure of THF is influenced by guest–host hydrogen bonding. THF molecules maintain a quasiregular array, reminiscent of the crystalline state, and their hydration structure (out to 5 Å) constitutes ~23H₂O. The local water structure in HDA is reminiscent of pure HDA-ice featuring 5-coordinated H₂O. In VHDA, the hydration structure of HDA is maintained but the local water structure is densified and resembles pure VHDA-ice with 6-coordinated H₂O. The hydration structure of THF in RA constitutes ~18 H₂O molecules and the water structure corresponds to a strictly 4-coordinated network, as in the liquid. Both VHDA and RA can be considered as homogeneous.« less

Dysprosium (Dy) has been studied using neutron diffraction under high pressures and low temperatures at a spallation neutron source by employing a large-volume diamond anvil cell. Companion measurements at different central wavelengths allow the collection over extended reciprocal space with momentum transfer Q covering the range from 0.5 Å^-1 to 5.5 Å^-1. Upon cooling to 15 K, magnetic ordering was observed in the hexagonal close-packed (hcp), alpha-samarium (α-Sm), and double hexagonal close packed (dhcp) phases of Dy to 22 GPa. We report on previously undetected magnetic superlattice reflections signaling antiferromagnetic transition for both the α-Sm and dhcp phases of Dy.more » Magnetic structure refinements for the α-Sm phase shows a complex phase comprising two magnetic propagation vectors k = (1/2, 1/2, 1/2) and k = (1/2, 0, 0). Magnetic structure refinements for the dhcp phase yield a single magnetic propagation vector k = (1/2, 0, 1/3) and a possible magnetic space group Pbnma. The refined magnetic structures are provided to the highest pressure of 22 GPa.« less

The Paris-Edinburgh press is a widely available, highly adaptable pressure cell commonly used while collecting neutron scattering data. Here, we detail the use of the VX3 and VX5 Paris-Edinburgh presses on the Wide-Angle Neutron Diffractometer (WAND²) at the High Flux Isotope Reactor at Oak Ridge National Laboratory. We first give a detailed overview of the instrument setup and alignment capabilities used at WAND². We then demonstrate the high pressure capabilities through three examples. In this work, the first example focuses on diffraction data obtained from a lithium-diamond mixture to 10 GPa with the use of single toroidal cubic boron nitridemore » anvils. Other examples include the room temperature compressions of germanium (up to 16 GPa) and the mineral malachite with double toroidal sintered diamond anvils. This work thereby represents the first studies above 10 GPa at the High Flux Isotope Reactor and opens the door for future user experiments at these elevated pressures.« less

SnO is known to undergo metallization at ~5 GPa while retaining its tetragonal symmetry. However, the mechanism of this metallization remains speculative. We present a combined experimental and computational study including pressure-dependent infrared spectroscopy, resistivity, and neutron powder diffraction measurements. We show that, while the excess charge mobility increases with pressure, the lattice distortion, in terms of the z-position of Sn, is reduced. Both processes follow a similar trend that consists of two stages, a moderate increment up to ~3 GPa followed by a rapid increase at higher pressure. This behavior is discussed in terms of polaron delocalization. The pressure-inducedmore » delocalization is dictated by the electron–phonon coupling and related local anisotropic lattice distortion at the polaron site. We show that these polaronic states are stable at 0 GPa with a binding energy of ~0.35 eV. Upon increasing the pressure, the polaron binding energy is reduced with the electron–phonon coupling strength of Γ and M modes, enabling the electrical phase transition to occur at ~3.8 GPa. Further compression increases the total electron–phonon coupling strength up to a maximum at 10 GPa, which is a strong evidence of dome-shaped superconductivity transition with T_c = 1.67 K.« less

High-pressure neutron diffraction is an extremely useful technique in the quest for making and understanding novel hydride superconductors. Neutron diffraction can be used to directly determine elemental stoichiometries and atomic positions of many light elements such as hydrogen or deuterium, even in the presence of heavy elements such as rare-earth metals. In this work, we report on the current status and ongoing developments on high-pressure neutron diffraction for hydride superconductors and other metal hydrides with a special focus on current advancements at the Spallation Neutrons and Pressure (SNAP) beamline of the Spallation Neutron Source at Oak Ridge National Laboratory. Formore » broader context, an overview of high-pressure neutron diffractometers and pressure cells is included together with insight into critical sample considerations. There, attention is given to the requirements for powdered hydride samples and the need for deuterium rather than hydrogen. Additionally, the advantages of angular access and data representation as possible at SNAP are described. We demonstrate the current capability for high-pressure neutron diffraction on two different samples created via hydrogen gas loading, specifically pure deuterium and nickel-deuteride. The deuterium example highlights the usefulness of adding sample materials that facilitate the formation of a good powder while the nickel-deuteride example demonstrates that atomic deuterium positions and stoichiometry can be directly determined. Both examples highlight the importance of large scattering apertures. These enable investigation of the data resolved by scattering angle that is needed to identify parasitic peaks and background features. Finally, future directions beyond current high-pressure neutron powder diffraction are also discussed.« less

Solid-state topochemical polymerization (SSTP) is a promising method to construct functional crystalline polymeric mate-rials, but contrast to various reactions happened in solution, only very limited types of SSTP reactions are reported. Diels-Alder (DA) and dehydro-DA (DDA) reaction are textbook reactions for preparing six-membered rings in solution, but scarcely seen in solid-state synthesis. Here, using multiple cutting-edge techniques, we demonstrate that the solid 1,4-diphenylbutadiyne (DPB) undergoes a DDA reaction under 10-20 GPa with the phenyl as the dienophile. The crystal structure at the critical pressure shows this reaction is “distance selected”. The distance of 3.2 Å between the phenyl and themore » phenylethynyl facilitates the DDA reaction, while the distances for other DDA and 1, 4-addition reactions are too large to allow the bonding. The obtained products are crystalline armchair graphitic nanoribbons, and hence our studies open a new route to construct the crystalline carbon materials with atomic-scale control.« less

Additively manufactured scattered beam collimators are increasingly being employed to boost the sample to cell peak signal ratio in high pressure neutron diffraction studies because of manufacturing versatility and performance improvements. We study how the measured diffraction pattern is affected by the presence of a collimator downstream of the sample, and develop a novel protocol that provides more effective background rejection. This protocol takes into account critical performance-determinants that were identified in this study, namely: (i) effectively identifying the collimator pattern on the detector; (ii) understanding the dependence of this pattern on sample and cell composition; and (iii) accurately identifyingmore » and differentiating the different regions of the pattern on the detector based on the dependency of the cell or sample and finally (iv) resolving the intensities at regions of the detector where neutrons scattered from the sample are preferentially represented, in order to boost the sample to cell peak signal ratio. Application of this novel analysis protocol is shown to increase the collimator performance over the traditional method.« less

A design for an incident-beam collimator for the Paris–Edinburgh pressure cell is described here. This design can be fabricated from reaction-bonded B₄C but also through fast turnaround, inexpensive 3D-printing. 3D-printing thereby also offers the opportunity of composite collimators whereby the tip closest to the sample can exhibit even better neutronic characteristics. Here, we characterize four such collimators: one from reaction-bonded B₄C, one 3D-printed and fully infiltrated with cyanoacrylate, a glue, one with a glue-free tip, and one with a tip made from enriched ¹⁰B₄C. The collimators are evaluated on the Spallation Neutrons and Pressure Diffractometer of the Spallation Neutron Sourcemore » and the Wide-Angle Neutron Diffractometer at the High Flux Isotope Reactor, both at Oak Ridge National Laboratory. This work clearly shows that 3D-printed collimators perform well and also that composite collimators improve performance even further. Beyond use in the Paris–Edinburgh cell, these findings also open new avenues for collimator designs as clearly more complex shapes are possible through 3D printing. An example of such is shown here with a collimator made for single-crystal samples measured inside a diamond anvil cell. These developments are expected to be highly advantageous for future experimentation in high pressure and other extreme environments and even for the design and deployment of new neutron scattering instruments.« less