arXiv subjects

Alexis Amouretti

Publications and source records attributed to Alexis Amouretti.

7 recordsLinked to original sources

arXiv2026

High Entropy Alloy under Shock Compression: Optical-Pump X-Ray-Probe

High entropy alloys (HEAs) are multi-principal-element alloys designed for tailorable mechanical performance and have been attracting significant engineering interest, yet their fundamental behaviour under extreme dynamic conditions, such as shock loading, remains unexplored. Here, we report laser-shock experiments on two different types of 1-micrometers-thick HEA microfilms, CuPdAgPtAu and CrFeCoNiCuMo, on 25-micrometers-thick black-Kapton ablator driven by a high intensity laser pulse (532 nm, 5 ns, 16 J, 0.5-mm diameter focal spot) and probed by an X-ray free electron laser (XFEL) pulse (12 keV, 7 fs). Time-resolved X-ray diffraction (XRD) shows the formation of a transient phase with a lattice compression up to 5.1% of the CuPdAgPtAu HEA along the (111) plane; this transient compressed phase existed for 0.3 ns. The impedance matching Hugoniot analysis estimated a shock pressure of 55 +/- 6 GPa in the HEA film, while Au- and Fe-based equations of state (EoS) modelling predict 80 GPa (0.8 MBar) at the free HEA surface. The free HEA surface reached maximum velocities of ~ 5 km/s as recorded from in situ monitoring with the velocity interferometry system for any reflector (VISAR) imaging. These initial HEA results show the suitability of HEA sample preparation and XFEL-based XRD characterisation under extreme shock loading, and are promising for experimental determination of the EoS of this emerging class of materials (beamtime proposal No.: 2024A8503 for a 6-hour preliminary experiment).

cond-mat.mtrl-sci↗

arXiv2025

Structural evolution of iron oxides melts at Earth's outer-core pressures

Oxygen and other light elements comprise up to 5 wt% of the Earth's outer-core, and may significantly influence its physical properties and the operation of the geodynamo. Here we report in situ x-ray diffraction measurements of Fe, Fe + 4.5 FeO (atomic proportion), and Fe2O3 melts at 177-438 GPa, achieved using laser-driven shock compression at an x-ray free-electron laser. The melts exhibit Fe-O coordination numbers between 4.0(0.4) and 4.5(0.4), indicating predominantly four-fold coordination environments. These coordination states are significantly smaller than those of Fe-bearing lower-mantle phases such as bridgmanite and ferropericlase. Shorter Fe-Fe interatomic distances in compressed iron oxide melts drive the denser packing relative to ambient melts, while the structural differences between Fe + 4.5 FeO and Fe2O3 melts under shock indicate that the oxidation state modulates oxygen solubility in liquid Fe. At around 177 GPa (380 km below the core-mantle boundary), Fe2O3 melts exhibit higher Fe-O coordination, suggesting that local variations in oxygen content could contribute to the stratification in the uppermost outer-core inferred from seismological and geomagnetic observations.

cond-mat.mtrl-sci↗

arXiv2025

A Momentum-Resolved X-ray Thomson Scattering Benchmark of Electronic-Response Models in Warm Dense Aluminium

The robust diagnosis of conditions generated in warm dense matter (WDM) experiments remains a persistent challenge. Here we describe the measurement of shock-compressed aluminium at 50 GPa with angle-resolved femtosecond x-ray Thomson scattering (XRTS) over a wide range of scattering wavevectors at the European XFEL. The measured plasmon dispersion and line shape show that the de facto standard approach for analysing XRTS spectra, based on uniform-electron-gas models, systematically overestimates the resonance energy by up to 8 eV. We present an ab initio approach that agrees within the experimental uncertainty and demonstrates that accounting for shock-induced disorder is critical for interpreting shock-compressed systems, providing evidence that ab initio treatments are required for reliable XRTS inference in warm dense aluminium.

physics.plasm-ph↗

arXiv2025

Phase transitions of eutectic high entropy alloy AlCoCrFeNi2.1 under shock compression

High entropy alloys (HEAs) are a new class of metals that exhibit unique mechanical performance. Among HEAs, additively manufactured eutectic high entropy alloys (AM-EHEAs) have recently emerged as candidate materials for use in extreme conditions due to their simultaneous high strength and ductility. However, the deformation and structural evolution of AM-EHEAs under conditions of high pressure have not been well characterized, limiting their use in extreme applications. We present dynamic compression experiments and molecular dynamics simulations studying the structural evolution of AM-EHEA AlCoCrFeNi2.1 when compressed to pressures up to 400 GPa. Our in-situ X-ray diffraction measurements capture the appearance of fcc and bcc phases at different pressure conditions, with pure- and mixed-phase regions. Understanding the phase stability and structural evolution of the AM EHEA offers new insights to guide the development of high-performance complex materials for extreme conditions.

cond-mat.mtrl-sci↗

arXiv2024

Shock-driven amorphization and melt in Fe$_2$O$_3$

We present measurements on Fe$_2$O$_3$ amorphization and melt under laser-driven shock compression up to 209(10) GPa via time-resolved in situ x-ray diffraction. At 122(3) GPa, a diffuse signal is observed indicating the presence of a non-crystalline phase. Structure factors have been extracted up to 182(6) GPa showing the presence of two well-defined peaks. A rapid change in the intensity ratio of the two peaks is identified between 145(10) and 151(10) GPa, indicative of a phase change. Present DFT+$U$ calculations of temperatures along Fe$_2$O$_3$ Hugoniot are in agreement with SESAME 7440 and indicate relatively low temperatures, below 2000 K, up to 150 GPa. The non-crystalline diffuse scattering is thus consistent with the - as yet unreported - shock amorphization of Fe$_2$O$_3$ between 122(3) and 145(10) GPa, followed by an amorphous-to-liquid transition above 151(10) GPa. Upon release, a non-crystalline phase is observed alongside crystalline $\alpha$-Fe$_2$O$_3$. The extracted structure factor and pair distribution function of this release phase resemble those reported for Fe$_2$O$_3$ melt at ambient pressure.

cond-mat.mtrl-sci↗

arXiv2024

Laser-driven shock compression and equation of state of Fe$_2$O$_3$ up to 700 GPa

We report here the first equation of state measurements of Fe$_2$O$_3$ obtained with laser-driven shock compression. The data are in excellent agreement with previous dynamic and static compression measurements at low pressure, and extend the known Hugoniot up to 700 GPa. We observe a large volume drop of $\sim$10% at 86 GPa, which could be associated, according to static compression observations, with the iron spin transition. Our measurements also suggest a change of the Hugoniot curve between 150 and 250 GPa. Above 250 GPa and within our error bars, we do not observe significant modifications up to the maximum pressure of 700 GPa reached in our experiment.

hep-ex↗

arXiv2022

Pushing the limits of flow strength in diamond

Extreme pressures and temperatures create conditions that allow even hard and brittle materials to deform plastically. Despite extensive research, the upper limits of flow strength, the resistance to plastic flow, remain uncertain, and the mechanisms driving deformation at the relevant stresses are a subject of debate. Using femtosecond in situ X-ray diffraction experiments and large-scale molecular dynamics simulations, we demonstrate that stacking fault-mediated strengthening enables shock-compressed nano-polycrystalline diamond to achieve a peak flow strength of 107+-5 GPa at a stress of 227+-8 GPa. Our findings show that extreme conditions can unlock unusual strength via mechanisms that can be used as design tools in targeted applications.

cond-mat.mtrl-sci↗