This study aims to resolve conflicting observations of bismuth’s high-pressure phase transitions across static, intermediate, and shock compression regimes. We probed its high-pressure structural sequence using the dynamic diamond anvil cell with and time-resolved X-ray diffraction with microsecond resolution at an X-ray free-electron laser. At room temperature and pressures up to 20 gigapascals, bismuth evolves through the same structural sequence previously identified under static compression. However, the transformation behavior differs in important ways under dynamic loading. In particular, the transition from the incommensurate intermediate-pressure phase to the high symmetry high pressure phase begins at pressures about 2 to 4 gigapascals lower than in static experiments, and the onset of this transformation depends on the compression rate. As a result, the stability field of the intermediate-pressure phase is reduced under rapid compression. Our results suggest that at sufficiently fast loading rates the intermediate phase may be bypassed entirely, consistent with previous shock-compression observations. Bismuth’s high-pressure phase transitions have shown conflicting results across different compression regimes. Here, the authors use dynamic diamond anvil cell experiments and time-resolved X-ray diffraction to reveal that rapid compression reduces the stability field of bismuth’s intermediate phase, suggesting potential bypassing of this phase, aligning with shock-compression findings.

Superconductivity in cuprates emerges out of a complex normal state that hosts density waves, pseudogap physics, and strange metal properties. Here, we access this normal state by synchronizing free-electron laser x-rays with high-magnetic-field pulses up to 44 T. We observe a linear increase in charge order amplitude and correlation length that persists far above the vortex melting transition. This behavior is incompatible with standard phase competition between charge order and superconductivity. By means of conventional hard x-ray diffraction and magnetostriction, we show that applied fields also enhance monoclinic lattice distortions. However, this magnetoelastic response is weaker and an epiphenomenon of the stripe order enhancement. Combined with recent observations of field-linear spin freezing, our results point to a direct coupling between magnetic field and the spin component of stripe order in the high-field normal state – a mechanism independent of superconductivity suppression that has so far remained hidden from scattering probes.

Color centers in diamond are promising single-photon sources for quantum technologies and biomedical applications. We studied the formation dynamics of negatively charged silicon-vacancy (SiV) centers during diamond nucleation using time-resolved X-ray pump-probe experiments at the European X-ray Free-Electron Laser Facility. A silicon-containing adamantane precursor was flash-heated within diamond anvil cells using ultrashort femtosecond X-ray pulses at a 2.2-MHz repetition rate. We captured the structural evolution of diamond with X-ray diffraction patterns separated by 443 ns. Correlating these dynamics with postexperiment SiV photoluminescence reveals, for the first time, a link between ultrafast diamond nucleation and color-center inclusion. SiV formation is contingent on diamond formation and occurs only above pressure-dependent energy-delivery-rate thresholds: 34.3 J·s-1 at 17.8 GPa and 178.4 J·s-1 at 14.4 GPa. Our findings define synthesis windows for generating SiV and reveal a kinetic regime in which diamond nucleates without optically active SiV, informing rate- and pressure-aware strategies for producing various color centers.

The development of pulsed intense x-ray sources, such as free electron laser, offers new avenues for high pressure experiments. Here, we study the feasibility and metrology of x-ray heating in diamond anvil cells at the European x-ray free electron laser. This method enables one to volumetrically heat the sample while inhibiting chemical migration and probing the crystallographic structure of the sample throughout the heating with a high repetition rate. We focus our study on iron, whose phase diagram is well established up to 100 GPa, to explore the possibilities and limitations of this technique. We volumetrically heat iron samples at starting pressures ranging from 10 to 138 GPa, using the x-ray beam pulsed at 4.5 MHz in a serial pump-and-probe experimental design. Experimental challenges arise from temperature gradients within the sample, changes in temperature at the 100 ns timescale, the difficulty of direct temperature estimates, the effect of thermal pressure, and the presence of metastable crystallites due to rapid cycles of heating and cooling. Hence, we develop a multi-crystal-like data processing method that allows us to account for sample heterogeneity in probed conditions. We then calibrate our measurements using known physical properties of iron under pressure. Thermal pressure in our experiments increases from 4% of the isochoric prediction at 10 GPa to 23% at 138 GPa, and we show that our data are in agreement with most previous observations of iron in this pressure range. The method can now be implemented at higher pressures and temperatures and on materials with unknown phase diagrams.

The alpha(bcc)-e(hcp) phase transition in polycrystalline Fe has been investigated under fast quasihydrostatic compression using piezoelectric actuator driven dynamic diamond anvil cells. X-ray diffraction data from Fe under intermediate strain rate compression were collected at megahertz repetition rates. Our results demonstrate, for the first time, the full evolution of the alpha-e phase transition in powder and foil samples at strain rates of '102 s-1. Under fast compression, the majority of the alpha phase transforms to e-Fe in a timescale of tens of microseconds, with a corresponding coexistence pressure of '2 GPa. The observed onset phase transition pressure of 13.4-14.4 GPa is in good agreement with the results of previous quasihydrostatic compression studies, suggesting that the transition is not influenced by compression rates up to '80 TPa s-1.

The crystallographic structure of iron under extreme conditions is a key benchmark for cutting-edge experimental and numerical methods. Moreover, it plays a crucial role in understanding planetary cores, as it significantly influences the interpretation of observational data and, consequently, insights into their internal structure and dynamics. However, even the structure of pure solid iron under the Earth's core conditions remains uncertain, with the commonly expected hexagonal close-packed structure energetically competitive with various cubic lattices. In this study, iron was compressed in a diamond anvil cell to above 200 GPa, and dynamically probed near the melting point using MHz frequency X-ray pulses from the European X-ray Free Electron Laser. The emergence of an additional diffraction line at high temperatures suggests the formation of an entropically stabilized bcc structure. Rapid heating and cooling cycles captured intermediate phases, offering new insights into iron's phase transformation paths. The appearance of the bcc phase near melting at extreme pressures challenges current understanding of the iron phase diagram under Earth's core conditions.

Thermal conductivity of Earths lower mantle controls heat transfer across the core-mantle boundary (CMB) and strongly influences mantle convection. We report direct measurements of the thermal conductivity of single-crystal ferropericlase (Mg_1-xFe_xO, x = 0.09-0.13), the second most abundant lower-mantle mineral, using optical laser flash and X-ray free-electron laser heating in diamond-anvil cells up to ∼2200 K and 130 GPa. These experiments provide the first conductivity data for ferropericlase at simultaneous lower-mantle pressures and temperatures. A marked reduction in conductivity between 60 and 100 GPa at ∼1700 K is consistent with the iron spin crossover. Combined with our previous results for Fe- and Fe,Al-bearing bridgmanite, the data define a lower-mantle conductivity profile that increases with pressure to ∼10 W m^-1 K^-1 near the CMB, constraining mantle heat flux, plume buoyancy, and long-term geodynamic evolution.

Gold ist ein unreaktives Metall und seine chemische Wechselwirkung mit Wasserstoff wird erst seit Kurzem untersucht. Unter Verwendung verschiedener Kohlenwasserstoffe als Wasserstoffquelle beobachten wir hier die Bildung von festem Goldhydrid in der Diamantstempelzelle, die mit einem Freie‐Elektronen‐Laser beheizt wird. Bei Drücken oberhalb von 40 GPa und bei Temperaturen in der Nähe des Schmelzpunkts bildet sich eine hexagonale Phase, die einem Hydrid mit der Stöchiometrie entspricht, wobei x mit dem Druck (40 bis 80 GPa) von 0 auf nahezu 1 ansteigt. Es handelt sich um eine Hochtemperaturphase, die sich beim Abkühlen auf 295 K in flächenzentriertes kubisches Gold umwandelt. Begleitende DFT‐MD‐Simulationen stimmen hervorragend mit den Ergebnissen der Experimente überein und zeigen, dass die Struktur aus einem hexagonal dicht gepackten Goldgitter mit ungeordneten Wasserstoffatomen in den Zwischenräumen besteht. Der Wasserstoff ist superionisch, d.h. er weist eine hohe Diffusionsfähigkeit durch das kristalline Goldgitter auf. Unsere Ergebnisse weisen die erste binäre Verbindung aus Gold und Wasserstoff im festen Zustand nach.

CoRDIA (Continuous Readout Digitizing Imager Array) is a hybrid pixel detector development targeted to 4 th generation synchrotron sources and (continuous) high-rate Free Electron Lasers. Serving the latter it builds upon the concept of the AGIPD detector, employing a charge sensitive preamplifier with adaptive gain switching. The further signal path comprises of a Correlated Double Sampling stage and an 11 bit Analogue to Digital Converter (ADC), serving a sub array of 16 pixels. 128 ADCs connect to a multi-gigabit serial link to drive the images off chip. For this part CoRDIA adopts the ” GWT-CC ” implementation on the Timepix4 chip by Nikhef. A chip with 256 × 192 pixels will implement 24 of these blocks. Since the links conform to industry standards (IEEE 802.3ae), the subsequent data acquisition can be based on commercial components. Performance targets are a continuous frame rate of ≈ 150 kHz, single-photon sensitivity at <12 keV, and a dynamic range of a few thousand photons (@ 12 keV) with a silicon sensor. The energy range could be extended using active sensors or sensors from ” high-Z ” materials towards lower and higher photon energies.

Various metastable ice phases and their complicated transition pathways have been found by pressurization at low temperatures at which slow kinetics and high metastability are easily achieved. By contrast, such diversity is less expected at room or elevated temperatures. Here, using a combination of a dynamic diamond anvil cell and X-ray free electron laser techniques, we demonstrate that supercompressed water transforms into ice VI through multiple freezing-melting pathways at room temperature, hidden within the pressure region of ice VI. These multiple transition pathways occur via a metastable ice (more specifically, ice XXI with body-centred tetragonal structure ( I 4 ¯ 2 d )) discovered in this study and a metastable ice VII that exists within the pressure range of ice VI. We find that supercompressed water structurally evolves from high-density water to very-high-density water, causing multiple transition pathways. These findings provide an insight to find more metastable ice phases and their transition pathways at elevated temperatures.

Gold is an unreactive metal and its chemical interactions with hydrogen have only recently been explored. Here, we report the formation of gold hydride above 40 GPa and 2200 K in X‐ray free electron laser heated diamond anvil cells using various hydrocarbons as hydrogen sources. Above 40 GPa, a hexagonal phase emerges close to the gold melting point, corresponding to a hydride with stoichiometry , with increasing from 0 to near 1 with pressure from 40 to 80 GPa. This is a high‐temperature phase which reverts to face centered cubic gold on cooling to 295 K. Accompanying DFT‐MD simulations are in excellent agreement with experiment and reveal the structure to consist of an hexagonal close packed gold lattice with atomic hydrogen disordered in the interstices. The hydrogen is superionic and exhibits high diffusivity through the crystalline gold lattice. Our results present the first solid‐state binary compound of gold and hydrogen.

The CoRDIA project aims to develop an X-ray imager capable of continuous operation in excess of 100 kframe/s. The goal is to provide a suitable instrument for Photon Science experiments at diffraction-limited Synchrotron Rings and Free Electron Lasers considering Continuous Wave operation. Several chip prototypes were designed in a 65 nm process: in this paper we will present an overview of the challenges and solutions adopted in the ASIC design.

The past, current and planned future developments of X-ray imagers in the Photon-Science Detector Group at DESY-Hamburg is presented. the X-ray imagers are custom developed and tailored to the different X-ray sources in Hamburg, including the storage ring PETRA III/IV; the VUV-soft X-ray free electron laser FLASH, and the European Free-Electron Laser. Each source puts different requirements on the X-ray detectors, which is described in detail, together with the technical solutions implemented.

The thermal conductivity of bridgmanite, the primary constituent of the Earth's lower mantle, has been investigated using diamond anvil cells at pressures up to 85 GPa and temperatures up to 3,100 K. We report the results of time-domain optical laser flash heating and X-ray Free Electron Laser heating experiments from a variety of bridgmanite samples with different Al and Fe contents. The results demonstrate that Fe or Fe,Al incorporation in bridgmanite reduces thermal conductivity by about 50% in comparison to end-member MgSiO3 at the pressure-temperature conditions of Earth's lower mantle. The effect of temperature on the thermal conductivity at 28-60 GPa is moderate, well described as k = k(300)(300/ T)(a), where a is 0.2-0.5. The results yield thermal conductivity of 7.5-15 W/(m x K) in the thermal boundary layer of the lowermost mantle composed of Fe,Al-bearing bridgmanite.

The European X-ray Free Electron Laser (European XFEL) is a cutting-edge user facility that generates per second up to 27,000 ultra-short, spatially coherent X-ray pulses within an energy range of 0.26 to more than 20 keV. Specialized instrumentation, including various 2D X-ray detectors capable of handling the unique time structure of the beam, is required. The one-megapixel AGIPD (AGIPD1M) detectors, developed for the European XFEL by the AGIPD Consortium, are the primary detectors used for user experiments at the SPB/SFX and MID instruments. The first AGIPD1M detector was installed at SPB/SFX when the facility began operation in 2017, and the second one was installed at MID in November 2018. The AGIPD detector systems require a dedicated infrastructure, well-defined safety systems, and high-level control procedures to ensure stable and safe operation. As of now, the AGIPD1M detectors installed at the SPB/SFX and MID experimental end stations are fully integrated into the European XFEL environment, including mechanical integration, vacuum, power, control, data acquisition, and data processing systems. Specific high-level procedures allow facilitated detector control, and dedicated interlock systems based on Programmable Logic Controllers ensure detector safety in case of power, vacuum, or cooling failure. The first 6 years of operation have clearly demonstrated that the AGIPD1M detectors provide high-quality scientific results. The collected data, along with additional dedicated studies, have also enabled the identification and quantification of issues related to detector performance, ensuring stable operation. Characterization and calibration of detectors are among the most critical and challenging aspects of operation due to their complex nature. A methodology has been developed to enable detector characterization and data correction, both in near real-time (online) and offline mode. The calibration process optimizes detector performance and ensures the highest quality of experimental results. Overall, the experience gained from integrating and operating the AGIPD detectors at the European XFEL, along with the developed methodology for detector characterization and calibration, provides valuable insights for the development of next-generation detectors for Free Electron Laser X-ray sources.

The pressure and temperature conditions at which precipitation of diamond occurs from hydrocarbon mixtures is important for modelling the interior dynamics of icy planets. However, there is substantial disagreement from laboratory experiments, with those using dynamic compression techniques finding much more extreme conditions are required than in static compression. Here we report the time-resolved observation of diamond formation from statically compressed polystyrene, (C 8 H 8 ) n , heated using the 4.5 MHz X-ray pulse trains at the European X-ray Free Electron Laser facility. Diamond formation is observed above 2,500 K from 19 GPa to 27 GPa, conditions representative of Uranus’s and Neptune’s shallow interiors, on 30 μs to 40 μs timescales. This is much slower than may be observed during the ∼10 ns duration of typical dynamic compression experiments, revealing reaction kinetics to be the reason for the discrepancy. Reduced pressure and temperature conditions for diamond formation has implications for icy planetary interiors, where diamond subduction leads to heating and could drive convection in the conductive ice layer that has a role in their magnetic fields.

Various metastable ice phases and their complicated transition pathways have been found by pressurization at low temperatures, where slow kinetics and high metastability can be easily achieved. In contrast, such diversity is less expected at room or elevated temperatures. Here, using a dynamic diamond anvil cell and X-ray free electron laser techniques, we demonstrate that supercompressed water transforms into ice VI through multiple freezing–melting pathways at room temperature, hidden within the pressure region of ice VI. The multiple transition pathways occur via a new metastable ice and a metastable ice VII in the supercompressed water. We found that the structural evolution of supercompressed water from high density to very high density underlies the multiple transition pathways. These findings provide new insights to find more metastable ice phases and their transition pathways at room or elevated temperatures on icy planets.

AbstractH2O transforms to two forms of superionic (SI) ice at high pressures and temperatures, which contain highly mobile protons within a solid oxygen sublattice. Yet the stability field of both phases remains debated. Here, we present the results of an ultrafast X-ray heating study utilizing MHz pulse trains produced by the European X-ray Free Electron Laser to create high temperature states of H2O, which were probed using X-ray diffraction during dynamic cooling. We confirm an isostructural transition during heating in the 26-69 GPa range, consistent with the formation of SI-bcc. In contrast to prior work, SI-fcc was observed exclusively above ~50 GPa, despite evidence of melting at lower pressures. The absence of SI-fcc in lower pressure runs is attributed to short heating timescales and the pressure-temperature path induced by the pump-probe heating scheme in which H2O was heated above its melting temperature before the observation of quenched crystalline states, based on the earlier theoretical prediction that SI-bcc nucleates more readily from the fluid than SI-fcc. Our results may have implications for the stability of SI phases in ice-rich planets, for example during dynamic freezing, where the preferential crystallization of SI-bcc may result in distinct physical properties across mantle ice layers.

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.