The Fe-Mn-based alloys are receiving immense attention due to their applications in the third generation of advanced high-strength steels, owing to their high strength and ductility. A detailed in situ high-pressure structural phase transformation and microstructural evolution in nanograined Fe-7%Mn alloy has been performed using the axial synchrotron X-ray diffraction technique. The ambient BCC phase of Fe-7%Mn undergoes pressure-driven structural PT to the HCP phase at 11.4 GPa. Both BCC and HCP phases coexist up to 15.9 GPa; thereafter, they transform into a pure HCP phase, which remains stable up to the maximum pressure of 30.3 GPa. The XRD study reveals that the (110)_b dense crystallographic plane of the BCC lattice transforms into a densely packed (002)_h peak of the HCP lattice following the orientational relationship (110)_b∥ (0001)_h via diffusionless Burger's martensitic crystallographic PT pathway. The evolution of crystallite size and microstrain with pressure shows a distinct change during the structural PT. The microstrain exhibits a sharp anomaly at around 10 GPa, suggesting that the microstructural changes precede the structural PT.

In laser-heated diamond anvil cell (DAC) experiments, the effective heated region typically decreases in size with increasing pressure, leading to steeper thermal gradients. Under these conditions, chromatic aberration in the optical path from sample to detector can significantly create bias in spectro-radiometric temperature measurement. We present a radiance-mapping approach using a hyperspectral camera that records 25 spectral channels spanning 605-875 nm at each pixel in a single exposure, providing spatially and spectrally resolved radiance in each frame. This enables chromatic effects to be recorded and corrected in data processing. We developed a procedure for hyperspectral mapping, involving per-camera calibration, crosstalk removal, measured spectral throughput functions, and optional sub-pixel co-registration to minimize chromatic distortion. The calibrated radiance maps are then used to derive temperature maps of the laser-heated hotspots. For smaller heating spots, the radiance mapping approach reveals chromatic shifts that conventional spectro-radiometric methods cannot quantify. Ambient-pressure heating experiments confirm accurate temperature retrieval. At high pressure, application of the hyperspectral system to a platinum-heating experiment at 12 GPa demonstrates stable temperature reconstruction under steep thermal gradients. Beyond mitigating chromatic aberrations, the ability to diagnose optical artifacts separately from emissivity variations during controlled test experiments or in situ suggests a path toward more rigorous spectral emissivity analysis and improved modeling of thermal transport in laser-heated DAC experiments.

Studying materials under extreme pressure in diamond anvil cells (DACs) is key to discovering emergent states of matter, yet no method currently allows the direct measurement of the electronic structure in this environment. Solid-state high-harmonic generation (sHHG) offers a unique all-optical window into the electronic structure of materials. We demonstrate sHHG spectroscopy inside a DAC by probing 2H-MoS2, up to 30 GPa, revealing a pressure-induced crossover of the lowest direct bandgap from the K-point to the [Formula: see text]-point. This transition manifests as a sharp minimum in harmonic intensity and a 30° rotation of the sHHG polarization anisotropy, despite the absence of a structural phase change. First-principles simulations attribute these features to interference between competing excitation pathways at distinct points in the Brillouin zone. Our results establish sHHG as a sensitive probe of electronic transitions at high pressure, enabling access to quantum phenomena that evade detection by conventional techniques.

The high-temperature compression behavior of lithium fluoride (LiF) has been determined to -80 GPa and 2300 K by means of high-resolution synchrotron-based x-ray diffraction in a laser-heated diamond-anvil cell. The room-temperature Vinet equation of state (EOS) for LiF yields an isothermal room-temperature, ambient-pressure lattice parameter a0 = 4.028 (+0.003) & Aring;, volume V0 = 65.35 (+0.03) & Aring;3, bulk modulus K0 = 67.57 (+0.34) GPa, and its pressure derivative K0' = 4.64 (+0.03). This expanded experimental dataset is in good agreement with the LiF thermal equation of state by Myint et al. (2019) up to -2300 K and 25 GPa. At higher pressures and temperatures our data shows reduced thermal expansion compared to the prediction and may be particularly important for experiments at more extreme conditions.

Understanding how microscopic structural domains govern macroscopic electronic properties is central to advancing hydride superconductors, yet such correlations remain poorly resolved under pressure. We report the synthesis and characterization of (La0.9Y0.1)H10 superhydrides exhibiting coexisting cubic Fm3̅m and hexagonal P6_3/mmc clathrate phases observed over the pressure range from 168 GPa down to 136 GPa. Using synchrotron-based X-ray diffraction imaging at the upgraded Advanced Photon Source, we spatially resolved μm-scale distributions of these phases, revealing structural inhomogeneity across the sample. Four-probe resistance measurements confirmed superconductivity with two distinct transitions: an onset at 244 K associated with the cubic phase and a second near 220 K linked to the hexagonal phase. Notably, resistance profiles collected from multiple current and voltage permutations showed variations in transition width and onset temperature that correlated with the spatial phase distribution. These findings demonstrate a direct connection between local structural domains and superconducting behavior. The authors report the synthesis of (La0.9Y0.1)H10 superhydrides and their characterization using synchrotron-based, spatially resolved x-ray diffraction and electrical transport imaging. They reveal μm-scale structural inhomogeneity with coexisting cubic and hexagonal clathrate phases exhibiting distinct superconducting transition temperatures.

At ambient conditions, the high-entropy alloy superconductor Re0.6(NbTiZrHf)0.4 exhibits exceptional mechanical properties among high-entropy alloys, with its hexagonal phase achieving nanoindentation hardness of 18.5 GPa. We report on a unique pressure-induced structural transformation from a hexagonal phase to a body-centered cubic (BCC) phase, revealed by synchrotron x-ray diffraction measurements up to 70 GPa. This first-order transition, accompanied by a 6.1% volume collapse, occurs at 44 GPa and results in a BCC structure with random site occupancy by the five constituent elements, which is remarkably retained upon decompression to ambient conditions. The transformation proceeds via a martensiticlike, diffusionless mechanism without elemental segregation, enabled by pressure-induced electronic redistribution and atomic-scale disorder. These findings demonstrate a rare case of metastable phase retention in a chemically complex alloy and offer new insights into structure-stability relationships under pressure.

We report the synthesis and characterization of (La0.9Y0.1)H10 superhydrides exhibiting coexisting cubic Fm-3m and hexagonal P63/mmc clathrate phases observed over the pressure range from 168 GPa down to 136 GPa. Using synchrotron-based X-ray diffraction imaging (XDI) at the upgraded Advanced Photon Source (APS-U), we spatially resolved micron-scale distributions of these phases, revealing structural inhomogeneity across the sample. Four-probe DC resistance measurements confirmed superconductivity, with two distinct transitions: an onset at 244 K associated with the cubic phase and a second near 220 K linked to the hexagonal phase. Notably, resistance profiles collected from different current and voltage permutations showed variations in transition width and onset temperature that correlated with the spatial phase distribution mapped by XDI. These findings demonstrate a direct connection between local structural domains and superconducting behavior. Yttrium substitution is found to influence both the phase behavior and superconducting properties of LaH10-type clathrate hydrides. More broadly, this study highlights the utility of spatially correlating structural and electrical transport measurements in materials exhibiting heterogeneity under pressure, including hydride superconductors.

Retraction of 'Carbon content drives high temperature superconductivity in a carbonaceous sulfur hydride below 100 GPa' by G. Alexander Smith et al., Chem. Commun., 2022, 58, 9064-9067, https://doi.org/10.1039/D2CC03170A.

The density evolution of the physical properties of the transition-metal oxide RuO2 coupled with a deeper understanding of underlying metastable phases is necessary for correlating universality between similar binary systems. Here, we report the pressure-temperature electrical resistance dependency with the structural evolution of RuO2. Conducting quasi-four-probe electrical transport measurements in a diamond anvil cell, a low-temperature loss of metallicity is observed above 28 GPa. This insulative transition is accompanied by a significant drop in pressure, suggesting the electronic transition is linked to a first-order structural phase transition. This is supported by the observation that the insulative electronic state is retained upon warming to room temperature. Density functional theory simulations indicate that the insulative fluorite-type phase can be favorable around these conditions and would exhibit a similar pressure difference through an isochoric transformation from the metallic HP-PdF2-type phase, however there is insufficient experimental evidence to confirm the presence of the fluorite-type phase. Furthermore, a unique arsenopyrite-type phase of RuO2 is observed with x-ray diffraction of a post-laser-heated sample at 62 GPa.

A reversible density driven insulator to metal to insulator transition in high-spin MnS_{2} is experimentally observed, leading with a colossal electrical resistance drop of 10^{8}  Ω by 12 GPa. Density functional theory simulations reveal the metallization to be unexpectedly driven by previously unoccupied S_{2}^{2-} σ_{3p}^{*} antibonding states crossing the Fermi level. This is a unique variant of the charge transfer insulator to metal transition for negative charge transfer insulators having anions with an unsaturated valence. By 36 GPa the emergence of the low-spin insulating arsenopyrite (P2_{1}/c) is confirmed, and the bulk metallicity is broken with the system returning to an insulative electronic state.

Controlling the formation and stoichiometric content of the desired phases of materials has become of central interest for a variety of fields. The possibility of accessing metastable states by initiating reactions by X-ray-triggered mechanisms over ultrashort time scales has been enabled by the development of X-ray free electron lasers (XFELs). Utilizing the exceptionally high-brilliance X-ray pulses from the EuXFEL, we report the synthesis of a previously unobserved yttrium hydride under high pressure, along with nonstoichiometric changes in hydrogen content as probed at a repetition rate of 4.5 MHz using time-resolved X-ray diffraction. Exploiting non-equilibrium pathways, we synthesize and characterize a hydride in a Weaire-Phelan structure type at pressures as low as 125 GPa, predicted using a crystal structure search, with a hydrogen content of 4.0-5.75 hydrogens per cation, that is enthalpically metastable on the convex hull.

The pressure–volume equations of state of palladium and rhodium statically compressed in neon are presented. Vinet fits give parameters for palladium: V0=58.678(73) Å3, B0=189.3(30) GPa, B0′=5.473(63), and rhodium: V0=55.062(63) Å3, B0=241.3(65) GPa, B0′=5.34(24). Both metals are observed to react with hydrocarbons under pressure to form hydrides. Existing equations of state are discussed with regard to potential inadvertent hydrogen contamination as a source for discrepancies and anomalous fitted parameters.

A MHz X-ray diffraction set-up for the investigation of material behaviour under dynamic compression in a diamond anvil cell at intermediate strain rates has been developed at the High Energy Density (HED) instrument at the European XFEL.

We have analysed SnO 2 with a combination of synchrotron X-ray diffraction and X-ray absorption spectroscopy across a pressure range of 0 → 82.9 GPa with thermal annealing by a CO 2 laser allowing access to all of the known high-density polymorphs of SnO 2 , and here report their crystallographic information. The metastability of the post-rutile α - PbO 2 and PdF 2 structures in SnO 2 are investigated by experiment and PW-DFT simulations, revealing a complex energetic landscape and suggesting a significant dependence of the observed phases on the pressure–temperature pathway taken in experiment. This article is part of the theme issue ‘Exploring the length scales, timescales and chemistry of challenging materials (Part 1)’.

Dehydrogenation of alkanes is of increasing importance in fulfilling global demand for olefins and offers a potential source of carbon‐neutral hydrogen as a co‐product. Currently commercial dehydrogenation processes occur at high‐temperatures (500–900 °C) which is energy intensive and results in side reactions and rapid coking of the catalysts. In addition, the hydrogen produced is often burned to maintain temperature and to inhibit the back reaction. Here, pressure is utilized as a parameter to enable novel chemical catalytic processes, and ambient‐temperature dehydrogenation of alkanes by palladium is observed at 50–100 MPa, with both hydrogen gas and olefins recovered on decompression. This reaction follows a fundamentally different path to current commercial high‐temperature low‐pressure dehydrogenation processes with the palladium catalyst reversibly forming a hydride intermediate.

The phenomenon of high temperature superconductivity, approaching room temperature, has been realized in a number of hydrogen-dominant alloy systems under high pressure conditions1-12. A significant discovery in reaching room temperature superconductivity is the photo-induced reaction of sulfur, hydrogen, and carbon that initially forms of van der Waals solids at sub-megabar pressures. Carbonaceous sulfur hydride has been demonstrated to be tunable with respect to carbon content, leading to different superconducting final states with different structural symmetries. A modulated AC susceptibility technique adapted for a diamond anvil cell confirms a Tc of 260 kelvin at 133 GPa in carbonaceous sulfur hydride. Furthermore, direct synchrotron infrared reflectivity measurements on the same sample under the same conditions reveal a superconducting gap of ~85 meV at 100 K in close agreement to the expected value from Bardeen-Cooper-Schrieffer (BCS) theory13-18. Additionally, x-ray diffraction in tandem with AC magnetic susceptibility measurements above and below the superconducting transition temperature, and as a function of pressure at 107-133 GPa, reveal the Pnma structure of the material is responsible for the close to room-temperature superconductivity at these pressures.

Retraction of DOI: 10.1103/PhysRevLett.127.016401.

feedthroughs from the bulkhead of a high-pressure gas loading apparatus.[9] The gears consist of 2 drive gears, which are manually turned through the bulkhead, and 4 driven gears which turn the DAC pressure screws. The gearing is configured at 1:1 ratio. The 4 driven gears are sprung, allowing the device to switch between two modes – free-spinning and engaged. When not in contact with the DAC pressure The uniaxial compression design of the diamond anvil high pressure cell (DAC) necessitates the use of a soft pressure-transmitting medium (PTM) to minimize non-hydrostatic effects at significantly high pressures, and many such media are gaseous at ambient conditions. There now exist a number of commercially-available instruments – high-pressure gas loading apparatus – for the insertion of gases into the diamond anvil cell up to several kbar. These machines allow the use of gases as a PTM, as a reagent for high-pressure chemistry, or to be loaded as the sample material itself. We present the development of two highly adaptable gearbox designs to allow the controlled closure of the DAC within an atmosphere of gas at several kbar, contained within the walls of a pressure vessel. The first applies a torque directly to the pressure screws and is thus DAC-specific, while the second applies a load to the body of the cell and may be used with a wide variety of DAC designs.