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1. Dynamic optical spectroscopy and pyrometry of static targets under optical and x-ray laser heating at the European XFEL

   https://doi.org/10.1063/5.0142196  

   Ball, O_B; Prescher, C.; Appel, K.; Baehtz, C.; Baron, M_A; Briggs, R.; Cerantola, V.; Chantel, J.; Chariton, S.; Coleman, A_L; et al (August 2023, Journal of Applied Physics)

   Experiments accessing extreme conditions at x-ray free electron lasers (XFELs) involve rapidly evolving conditions of temperature. Here, we report time-resolved, direct measurements of temperature using spectral streaked optical pyrometry of x-ray and optical laser-heated states at the High Energy Density instrument of the European XFEL. This collection of typical experiments, coupled with numerical models, outlines the reliability, precision, and meaning of time dependent temperature measurements using optical emission at XFEL sources. Dynamic temperatures above 1500 K are measured continuously from spectrally- and temporally-resolved thermal emission at 450–850 nm, with time resolution down to 10–100 ns for 1–200 μs streak camera windows, using single shot and integrated modes. Targets include zero-pressure foils free-standing in air and in vacuo, and high-pressure samples compressed in diamond anvil cell multi-layer targets. Radiation sources used are 20-fs hard x-ray laser pulses at 17.8 keV, in single pulses or 2.26 MHz pulse trains of up to 30 pulses, and 250-ns infrared laser single pulses. A range of further possibilities for optical measurements of visible light in x-ray laser experiments using streak optical spectroscopy are also explored, including for the study of x-ray induced optical fluorescence, which often appears as background in thermal radiation measurements. We establish several scenarios where combined emissions from multiple sources are observed and discuss their interpretation. Challenges posed by using x-ray lasers as non-invasive probes of the sample state are addressed. 

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2. High‐Pressure Deformation of Iron–Nickel–Silicon Alloys and Implications for Earth’s Inner Core

   https://doi.org/10.1029/2020JB021077  

   Brennan, Matthew C.; Fischer, Rebecca A.; Couper, Samantha; Miyagi, Lowell; Antonangeli, Daniele; Morard, Guillaume (March 2021, Journal of Geophysical Research: Solid Earth)

   Abstract Earth’s inner core exhibits strong seismic anisotropy, often attributed to the alignment of hexagonal close‐packed iron (hcp‐Fe) alloy crystallites with the Earth’s poles. How this alignment developed depends on material properties of the alloy and is important to our understanding of the core’s crystallization history and active geodynamical forcing. Previous studies suggested that hcp‐Fe is weak under deep Earth conditions but did not investigate the effects of the lighter elements known to be part of the inner core alloy. Here, we present results from radial X‐ray diffraction experiments in a diamond anvil cell that constrain the strength and deformation properties of iron‐nickel‐silicon (Fe–Ni–Si) alloys up to 60 GPa. We also show the results of laser heating to 1650 K to evaluate the effect of temperature. Observed alloy textures suggest different relative activities of the various hcp deformation mechanisms compared to pure Fe, but these textures could still account for the theorized polar alignment. Fe–Ni–Si alloys are mechanically stronger than Fe and Fe–Ni; extrapolated to inner core conditions, Si‐bearing alloys may be more than an order of magnitude stronger. This enhanced strength proportionally reduces the effectivity of dislocation creep as a deformation mechanism, which may suggest that texture developed during crystallization rather than as the result of postsolidification plastic flow. 

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3. Detection of thin film phase transformations at high-pressure and high-temperature in a diamond anvil cell

   https://doi.org/10.1038/s43247-024-01234-9  

   Berrada, Meryem; Hu, Genzhi; Zhou, Dongyuan; Wang, Siheng; Nguyen, Phuong Q. H.; Zhang, Dongzhou; Prakapenka, Vitali; Chariton, Stella; Chen, Bin; Li, Jie; et al (February 2024, Communications Earth & Environment)

   Abstract Quantifying how grain size and/or deviatoric stress impact (Mg,Fe)₂SiO₄phase stability is critical for advancing our understanding of subduction processes and deep-focus earthquakes. Here, we demonstrate that well-resolved X-ray diffraction patterns can be obtained on nano-grained thin films within laser-heated diamond anvil cells (DACs) at hydrostatic pressures up to 24 GPa and temperatures up to 2300 K. Combined with well-established literature processes for tuning thin film grain size, biaxial stress, and substrate identity, these results suggest that DAC-loaded thin films can be useful for determining how grain size, deviatoric stress, and/or the coexistence of other phases influence high-pressure phase stability. As such, this novel DAC-loaded thin film approach may find use in a variety of earth science, planetary science, solid-state physics, and materials science applications. 

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4. Melting of the Fe‐C‐H System and Earth's Deep Carbon‐Hydrogen Cycle

   https://doi.org/10.1029/2022GL098919  

   Lai, Xiaojing; Zhu, Feng; Gao, Jing; Greenberg, Eran; Prakapenka, Vitali B.; Meng, Yue; Chen, Bin (July 2022, Geophysical Research Letters)

   Abstract The occurrences and cycling of slab‐originated carbon and hydrogen are considered to be controlled by their reactions with metallic iron from mantle disproportionation and slab serpentinization, to form Fe alloys containing carbon and hydrogen. Here we show experimental results on the phase relations and melting of the Fe‐C‐H system using laser‐heated diamond anvil cell and X‐ray diffraction techniques up to 72 GPa. The incorporation of hydrogen was found to lower the eutectic melting temperatures of Fe‐C alloy by ∼50–178 K at 20–70 GPa, facilitating the formation of metallic liquids in the deep mantle and thus enhancing the mobility and deep cycling of subducted carbon and hydrogen. Hydrogen also substitutes with carbon in Fe‐C metal to form hydride and diamond at relatively high‐temperature conditions (e.g., 42.6 GPa, >1885 K and 71.8 GPa, >1798 K). The hydrogen‐carbon‐enriched metallic liquids provide the necessary fluid environment for superdeep diamond growth. 

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5. The Bridgmanite–Akimotoite–Majorite Triple Point Determined in Large Volume Press and Laser-Heated Diamond Anvil Cell

   https://doi.org/10.3390/min10010067  

   Kulka, Britany L.; Dolinschi, Jonathan D.; Leinenweber, Kurt D.; Prakapenka, Vitali B.; Shim, Sang-Heon (January 2020, Minerals)

   null (Ed.)

   The bridgmanite–akimotoite–majorite (Bm–Ak–Mj or BAM) triple point in MgSiO3 has been measured in large-volume press (LVP; COMPRES 8/3 assembly) and laser-heated diamond anvil cell (LHDAC). For the LVP data, we calculated pressures from the calibration provided for the assembly. For the LHDAC data, we conducted in situ determination of pressure at high temperature using the Pt scale at synchrotron. The measured temperatures of the triple point are in good agreement between LVP and LHDAC at 1990–2000 K. However, the pressure for the triple point determined from the LVP is 3.9 ± 0.6 GPa lower than that from the LHDAC dataset. The BAM triple point determined through these experiments will provide an important reference point in the pressure–temperature space for future high-pressure experiments and will allow mineral physicists to compare the pressure–temperature conditions measured in these two different experimental methods. 

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