Engineering topics

Guthrie, Malcolm

Publications and source records attributed to Guthrie, Malcolm.

6 records

DOE OSTI2024

Cryogenic temperatures promote the pressure-induced polymorphic transition in CoCrFeMnNi high entropy alloy

Pressure-induced polymorphism has recently been demonstrated in several high entropy alloys. This offers a new window into the much-debated issue of phase selection and stability in these systems. Here, we examine the effect of cryogenic temperatures on the pressure-induced transition from face centered cubic to hexagonal close-packed structures of the prototype CoCrFeMnNi (Cantor) alloy. We observe a reduction in the critical pressure for the onset of the polymorphic transition as the temperature decreases, confirming the progressive stabilization of the hexagonal phase with decreasing temperature previously predicted by ab initio calculations accounting for magnetic interactions. We argue that in situ high-pressure experiments at cryogenic temperatures, which suppress time-dependent transformation triggered at higher temperatures, present a unique opportunity to significantly improve our understanding of these complex alloys.

alloys↗

DOE OSTI2023

Design, calibration, and performance of a uniaxial pressure cell for neutron scattering studies of quantum magnetism

Here we provide an overview of a pressure cell designed to apply uniaxial pressure to single crystals for the study, by neutron scattering techniques, of strongly correlated magnetic systems and, in particular, quantum magnets. A detailed overview of the pressure cell components, their requirements, and links to the scientific and technical specifications are presented. The pressure cell is able to accommodate a 200 mm 3 single crystal that can be pressurized up to 2 GPa at cryogenic temperatures. The pressure cell is consistent with the requirements of inelastic neutron scattering and, importantly, neutron polarization analysis. A particular strength of the uniaxial pressure cell is the highly uniform and low background for a wide scattering angle of 360° horizontally and ±20° vertically. We show the performance of the uniaxial pressure cell using a relevant neutron scattering instrument, the polarized diffuse scattering instrument, D7. The experiments confirm that the cell complies with the scientific and technical requirements. This uniaxial pressure cell will provide a useful additional tool in the sample environment suite available for the study of quantum magnetism.

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Advancing neutron diffraction for accurate structural measurement of light elements at megabar pressures

Over the last 60 years, the diamond anvil cell (DAC) has emerged as the tool of choice in high pressure science because materials can be studied at megabar pressures using X-ray and spectroscopic probes. In contrast, the pressure range for neutron diffraction has been limited due to low neutron flux even at the strongest sources and the resulting large sample sizes. Here, we introduce a neutron DAC that enables break-out of the previously limited pressure range. Key elements are ball-bearing guides for improved mechanical stability, gem-quality synthetic diamonds with novel anvil support and improved in-seat collimation. We demonstrate a pressure record of 1.15 Mbar and crystallographic analysis at 1 Mbar on the example of nickel. Additionally, insights into the phase behavior of graphite to 0.5 Mbar are described. These technical and analytical developments will further allow structural studies on low-Z materials that are difficult to characterize by X-rays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Development of Large-Volume-Diamond Anvil Cell for Neutron Diffraction: The Neutron Diamond Anvil Cell Project at ORNL

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. Here 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.

Boehler, Reinhard↗

DOE OSTI2021

Methods for neutron diffraction studies on hydride superconductors and other metal hydrides

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. For 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.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

On single-crystal neutron-diffraction in DACs: quantitative structure refinement of light elements on SNAP and TOPAZ

Quantitative single crystal neutron-diffraction in diamond anvil cells has so far been limited by the neutron flux available at the various neutron sources. As a result, highly precise measurements of the exact position of light elements have not been possible preventing, for example, structural studies of hydrogen and hydrogen bonds under pressure. Here we report experiments carried out on SNAP at the Spallation Neutron Source (ORNL, TN, USA) to explore the possibility and current limits of such studies. Furthermore, we benchmarked the obtained data quality with reference experiments carried out on TOPAZ, a dedicated single-crystal instrument.We show that measuring single-crystal diffraction intensities on SNAP is possible to such a precision that we are able to resolve the hydrogen bonds in potassium dideuterium phosphate (DKDP) as well as in ice VI.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗