Browsing by Author "McMahon, M. I."

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    High pressure structure of lanthanum
    (Cranfield University Defence and Security, 2024-11-13) Roy, Callum R.; Storm, C. V.; Munro, K.; McMahon, M. I.
    The behaviour of the lanthanum (La) metal at high pressure is of great interest because it provides insight into the behaviour of f electrons in high density metals, and also because high-pressure lanthanum hydrides have some of the highest superconducting temperatures known. Understanding the high-pressure phases of La is then vital in identifying the hydrogen content of these super-hydrides. However, the structure of La above 70 GPa is uncertain and a number of different, but related, structural forms have been reported in the literature. We have collected new, high-quality diffraction data to 230 GPa (2.3 Mbars) using the sub-micron diameter x-ray beam now available at the PETRA-III synchrotron. Analysis of this new data using Rietveld and Le Bail analysis reveals that La transforms to a body-centred tetragonal structure above ~80 GPa, a structure long-known in neighbouring element Ce, and confirming a previous unpublished experimental result from our group and a recent computational prediction.
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    Material strength at high pressure
    (Cranfield University Defence and Security, 2024-11-13) Lonsdale, C. M.; McHardy, J. D.; Storm, C. V.; Roy, C. R.; MacLeod, S. G.; McMahon, M. I.
    Over the past 30 years, advancements in the focusing schemes, beam quality, and X-ray brilliance at synchrotron light sources have enabled the reduction of X-ray beam dimensions from tens of micrometers into the sub-micrometer domain. These developments have enabled spatial mapping of the stress state at multi-megabar pressures in the diamond anvil cell. This work presents angle-dispersive X-ray diffraction results collected on beamline P02.2 at the Petra-III synchrotron using a beam size (FWHM) of 0.85 x 0.85 microns on an Ir sample. Variations in the local stress state in the sample were analysed through two approaches based on X-ray diffraction peak shifting and broadening. The results of the two methods are compared and highlight the effectiveness of Bi as a pressure transmitting medium, even at multi-megabar pressures. We look to apply these techniques to future experiments into obtaining more precise investigations of phase transitions and material strength at extreme pressure.