Understanding the behavior of the water-ammonia system at high pressure-high temperature conditions is important for modeling the internal dynamics of exoplanet icy mantles. Conventionally, mixtures of ammonia hemihydrate AHH (2:1 ammonia-water molar ratio) and H2O ice VII have been regarded as the ultimate solid phase assembly in the system. Here we report evidence for chemical reactions between AHH and ice VII above 750 K and 16 GPa that stabilize water-rich ammonia hydrates, including a novel ultra-water rich hydrate NH3.6H2O (1:6 ratio) coexisting with ammonia dihydrate ADH (1:2 ratio) and excess ice VII. This assembly is stable up to at least 30 GPa and 1600 K and can be quenched to room temperature. Our results demonstrate that water-rich ammonia hydrates are favored in the icy mantle of 1-2 MEarth exoplanets regardless of the ammonia content of the hydrate crystallized during accretion and/or evolution as long as excess H2O ice is available. The buoyancy contrast between water-rich hydrates and ice VII may lead to chemical stratification in exoplanet icy mantles, hence affecting their thermal evolution.

Single crystals of carbonic acid (H2CO3) were synthesized in a laser-heated diamond anvil cell at moderate pressures between 5 and 13 GPa by reacting H2O with CO2. Its monoclinic crystal structure (P21/n with Z = 4) has been obtained from synchrotron single-crystal X-ray diffraction experiments at ≈8 GPa. The positions of the hydrogen atoms have been determined from the experimental data. Density functional theory-based calculations in combination with experimental Raman spectroscopy confirmed the structural model derived from the diffraction data. This is the first single-crystal structure solution of water-free carbonic acid, H2CO3. The structural model provided here differs from structural models reported earlier for lower pressures derived from neutron powder diffraction data.

Talc, as an important class of clay minerals constituting subducting oceanic crust, has long been known to undergo interlayer expansion by ~6% to contain net ~13 wt.% water into the 'so-called' 10 Å phase. Although subduction fluid is mildly alkaline and includes various salts and other dissolved species, its effect on the stability of subducting minerals has not yet been considered. Here, we report that subducting talc, when exposed to alkaline salty water conditions, breaks down to form a super-hydrated 15 Å phase at ~3.0 GPa and ~350 °C, corresponding to a depth of ~90-95 km along a cold subduction geotherm. The 15 Å phase remains stable down to ~125 km depth, where it transforms into the previously known 10 Å phase. Our combined experimental and computational results show that the super-hydrated 15 Å phase contains net ~31 wt.% water through interlayer expansion by ~60%. Our work thus demonstrates mineral transformation under more realistic subduction environments, which calls for reevaluation of subduction-related geochemistry and seismicity as well as water transportation into the deep Earth.

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.

CoSb3 belongs to the skutterudite family of compounds and serves as a crucial platform for the exploration of thermoelectric materials, however, its importance is equally high for studies of strong correlations at high pressures. Under compression it undergoes a 'self-insertion' isostructural transition resulting in a peculiar redistribution of large Sb atoms between different crystallographic sites. We conducted a comprehensive investigation of the structural phase stability of CoSb3 up to 70 GPa using single crystal samples characterized employing conventional single crystal X-ray diffraction and X-ray scattering focused on measuring Bragg peak at high resolution (including elements of Bragg Coherent Diffraction Imaging). We explore the compression behavior of CoSb3 in three different pressure transmitting media (PTM) and address several important, but previously unexplored topics: the influence of various PTMs and nonhydrostatic stresses on the strongly correlated system of CoSb3, including the 'self-insertion' crossover, the phase stability of CoSb3, the compound's polymorphism, its crystal chemistry, and its peculiar evolution under pressure at ambient temperature. Among other important observations, we track the population of Sb atoms within the dodecahedral sites of CoSb3 on compression, during the process of 'self-insertion', and on decompression. We detect that 'self-insertion' may not only reduce the solid's compressibility, but also make it negative. Finally, but not least, we report that the 'self- insertion' crossover is an important step preceding a previously unknown phase transformation from cubic Im3 CoSb3 into trigonal R3 occurring above 40 GPa, and discuss the distinctive behavior of CoSb3 phases and their structural frameworks.

The crystal structure and the pressure-mediated crystal-fluid interaction of mesolite have been re-investigated by a multi-methodological approach, based on single-crystal neutron diffraction and by in-situ single-crystal synchrotron X-ray diffraction, using a diamond anvil cell. The structure refinement based on neutron intensity data collected at 20 K confirms the general model previously reported for mesolite, but largely improves the description of the hydrogen-bond network (with accurate sites location, their libration regime and interactions). Twelve out of the nineteen oxygen sites in the crystal structure of mesolite are involved in H-bonds as donors or as acceptors, reflecting the complex configuration of the H-bonding network. In the high-pressure investigations, four different pressure-transmitting fluids have been employed: the non-penetrating Daphne oil 7575 and the potentially penetrating methanol:ethanol:H2O (1:1:1) mixture, distilled H2O and liquid Ne. The Daphne oil 7575 experiment provided insight into the intrinsic compressional behaviour of mesolite, without any pressure-induced crystal-fluid interaction, yielding an isothermal bulk modulus KV0 = 55.9(7) GPa (beta V0 = 0.0179(2) GPa-1). In the aqueous mixtures, H2O molecules have been observed to continuously penetrate into the structural cavities, firstly in the natrolite-and then in the scolecite-type sheets, in the pressure range 0.8-1.9 GPa. By comparing the results of this study to the literature data, there is an apparent correlation between the pressure at which the adsorption process occurs and the H2O concentration of the pressure-transmitting medium: a higher H2O fraction allows the over-hydration of the scolecite-type sheets at lower pressures. When compressed in liquid Ne, atoms of neon appear to be able to penetrate into the natrolite-type sheets, interacting with the extra-framework population via weak van der Waals forces.

Melting temperatures of materials at high-pressure are one of the key physical properties that can be measured. However, large discrepancies in high-pressure melt lines exist between different experimental and theoretical approaches. In this paper, we present a novel approach for melting determination at high pressure where time-resolved synchrotron X-ray phase contrast imaging is used to observe the solid to liquid phase transition in laser heated samples in the diamond anvil cell along with simultaneous X-ray diffraction. Optical radiometric temperature measurements are correlated with the observed phase boundaries determined from X-ray phase contrast images and structural information from X-ray diffraction patterns to determine the melting temperature. We benchmarked this new technique with experiments on the high-pressure melting of platinum (Pt). Our new Pt melting results are compared with several recent studies on the high pressure melt line of Pt which utilized different techniques to determine melting. The technique can readily be applied to other materials and offers great potential for the determination of accurate and precise melting temperatures.

The effect of high pressure on ribavirin, a broad-spectrum antiviral consisting of ribofuranosyl triazole, and carboxamide moieties, has been studied up to ∼10 GPa. Three new high-pressure phases, designated V3, V4 and V5, have been obtained by compression of the ambient-pressure V2 form with structures refined up to 7.5 GPa. The new phases are formed at 5.3, 6.0, and 7.2 GPa, respectively, and crystallize in space group P212121 with Z' = 3, 1, and 1. They are distinguished by changes in the conformation of the ribofuranosyl moiety which impacts both the molecular geometry and the supramolecular structure.

X-ray free electron laser (XFEL) sources coupled to high-power laser systems offer an avenue to study the structural dynamics of materials at extreme pressures and temperatures. The recent commissioning of the DiPOLE 100-X laser on the high energy density (HED) instrument at the European XFEL represents the state-of-the-art in combining x-ray diffraction with laser compression, allowing for compressed materials to be probed in unprecedented detail. Here, we report quantitative structural measurements of molten Sn compressed to 85(5) GPa and ∼3500 K. The capabilities of the HED instrument enable liquid density measurements with an uncertainty of ∼1% at conditions which are extremely challenging to reach via static compression methods. We discuss best practices for conducting liquid diffraction dynamic compression experiments and the necessary intensity corrections which allow for accurate quantitative analysis. We also provide a polyimide ablation pressure vs input laser energy for the DiPOLE 100-X drive laser which will serve future users of the HED instrument.

The dynamic diamond anvil cell (dDAC) is a recently developed experimental platform that has shown promise for studying the behavior of materials at strain rates ranging from intermediate to quasi-static and shock compression regimes. Combining dDAC with time-resolved x-ray diffraction (XRD) in the radial geometry (i.e., with incident x-rays perpendicular to the axis of compression) enables the study of material properties such as strength, texture evolution, and deformation mechanisms. This work describes a radial XRD dDAC setup at beamline P02.2 (Extreme Conditions Beamline) at DESY's PETRA III synchrotron. Time-resolved radial XRD data are collected for titanium, zirconium, and zircon samples, demonstrating the ability to study the strength and texture of materials at compression rates above 300 GPa/s. In addition, the simultaneous optical imaging of the DAC sample chamber is demonstrated. The ability to conduct simultaneous radial XRD and optical imaging provides the opportunity to characterize plastic strain and deviatoric strain rates in the DAC at intermediate rates, exploring the strength and deformation mechanisms of materials in this regime.

A natural intermediate member of the scapolite solid solution {Me-47; chemical formula: (Na1.86Ca1.86K0.23Fe0.01)(Al(4.3)6Si(7.64))O-24[Cl-0.48(CO3)(0.48)(SO4)(0.01)]}, with the unusual I4/m space group, has been studied at various temperatures and combined high-T and high-P by means of in situ single-crystal and powder X-ray diffraction, using both conventional and synchrotron X-ray sources. In addition, single-crystal neutron diffraction data were collected at ambient-T and 685 degrees C. A fit of the experimental V-T data with a thermal equation of state yielded a thermal expansion coeficient at ambient conditions: alpha(V25 degrees C) = 1/V-0 center dot(partial derivative V/partial derivative T)(P,25 degrees C) = 1.74(3)center dot 10(-5) K-1. A comparative analysis of the elastic behavior of scapolite based on this study and previous high-T XRD data suggests that a thorough re-investigation of the diferent members of the marialite-meionite solid solution is needed to fully understand the role of crystal chemistry on the thermal behavior of these complex nonbinary solid solutions. The experimental data obtained within the full temperature range of analysis at ambient pressure confirm that the investigated sample always preserves the I4/m space group, and possible implications on the metastability of I4/m intermediate scapolite are discussed. Neutron difraction data show that no significant Si and Al rearrangement among the T sites occurs between 25 and 685 degrees C. The combined high-T and high-P data show that at 650 degrees C and between 10.30(5) and 10.71(5) GPa a phase transition toward a triclinic polymorph occurs, with a positive Clapeyron slope (i.e., dP/dT > 0). A comprehensive description of the atomic-scale structure deformation mechanisms induced by temperature and/or pressure, including those leading to structural instability, is provided based on single-crystal structure refinements.

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.

We synthesized CdC2O5 and a new high-pressure polymorph of CdCO3 by laser heating otavite, CdCO3, in CO2 at 43 GPa. The structure of CdC2O5 contains pyramidal [C4O10](4-) building blocks formed by [CO4] tetrahedra, where the carbon is in 4-fold coordination. In addition, we found a new monoclinic (P2(1)/c) high-pressure polymorph of CdCO3 with trigonal [CO3](2-) groups. Both new structures were characterized by single-crystal X-ray diffraction, Raman spectroscopy, and DFT calculations.

Understanding the phase behavior and structural properties of salt water at high pressures is essential for understanding the dynamics and physical characteristics of icy planets. In this study, we employed high-pressure experimental and ab initio simulation techniques to investigate the impact of $\mathrm{CaC}{\mathrm{l}}_{2}$ on the structure of ice VII. Our findings reveal that 1.8 mol% $\mathrm{CaC}{\mathrm{l}}_{2}$ can be incorporated into the ice VII structure above 10 GPa. This $\mathrm{CaC}{\mathrm{l}}_{2}$-bearing ice VII (Cb VII) exhibits a lower O-H stretching frequency in the Raman spectra as well as a reduced volume of the unit cell compared to pure ice VII. In contrast to doping ice VII with other salts such as LiCl and NaCl that leads to an increase of the ice VII to ice X transition pressure occurring at 100--150 GPa, $\mathrm{CaC}{\mathrm{l}}_{2}$ doping stands out by reducing the transition pressure. It shifts the transition to a pressure of 52 GPa, which is significantly lower than the transition pressure of 80 GPa in the pure ${\mathrm{H}}_{2}\mathrm{O}$ ice system. This notable distinction highlights the unique influence of $\mathrm{CaC}{\mathrm{l}}_{2}$ on the phase behavior of water under high pressure, and we attribute these effects to the phenomenon of chemical pressure induced by $\mathrm{CaC}{\mathrm{l}}_{2}$ within the ice VII structure. Our study suggests that the presence of a modified ice VII phase, contaminated with salt and referred to as Cb VII, may influence the composition, structure, and evolution of planets.

The high-pressure behaviour and the crystal -fluid interaction of zeolites with EAB topology were investigated by in -situ single -crystal and powder synchrotron X-ray diffraction, both on synthetic and natural samples. The experiments were conducted using a diamond anvil cell and different pressure transmitting fluids, including: the non -penetrating silicone oil and the potentially penetrating methanol:ethanol:H2O = 16:3:1 mixture, methanol and distilled H2O. The zeolites intrinsic compressional behaviour investigated with a non -penetrating fluid showed the significant role of the extra framework population on the bulk compressibility. Notably, within the first -0.5 GPa of the silicone oil ramp, the bulk modulus (KV0 = beta V0  1) resulted to be KV0 = 62(1) GPa for the natural bellbergite and KV0 = 16(4) GPa for the synthetic K -analogue. The synthetic EAB zeolites demonstrated a high host capacity for methanol molecules, which were not able to penetrate the natural bellbergite cavities. A comparative analysis between the behaviour of zeolites with EAB topology and structurally similar zeolites, such as erionite (ERI topology) and offretite (OFF), is provided.

The understanding of the origin of seismic anisotropy in the Earth’s inner core (IC) remains a subject of debate and requires examining the deformation behavior of potential core materials. In this research, we investigated the effect of silicon and carbon on the deformation of the hexagonal close-packed iron alloy employing radial X-ray diffraction at high-pressure, high-temperature conditions. We revealed the low anisotropy of the sound velocity (~2 %) of the Fe-Si-C alloy that is compatible with the anisotropy observed in the IC’s outer shells. This finding provides an explanation for the heterogeneous depth-dependent elastic anisotropy in the IC originating from the stratification of silicon and carbon within the inner core upon its crystallization.

Presented and discussed here is the implementation of a software solution that provides prompt X-ray diffraction data analysis during fast dynamic compression experiments conducted within the dynamic diamond anvil cell technique. It includes efficient data collection, streaming of data and metadata to a high-performance cluster (HPC), fast azimuthal data integration on the cluster, and tools for controlling the data processing steps and visualizing the data using the DIOPTAS software package. This data processing pipeline is invaluable for a great number of studies. The potential of the pipeline is illustrated with two examples of data collected on ammonia–water mixtures and multiphase mineral assemblies under high pressure. The pipeline is designed to be generic in nature and could be readily adapted to provide rapid feedback for many other X-ray diffraction techniques, e.g. large-volume press studies, in situ stress/strain studies, phase transformation studies, chemical reactions studied with high-resolution diffraction etc.

We have synthesized the first hydrous sp3-carbonate by laser-heating Ba[CO3], CO2 and H2O in a diamond anvil cell at 40(3) GPa. The crystal structure of Ba[H4C4O10][H3C4O10][H2CO3][HCO3] was determined by synchrotron single crystal X-ray diffraction. The experiments were complemented by DFT-based calculations. This compound is the first example of a carbonate containing both trigonally-coordinated carbon in [CO3]2--groups and tetrahedrally coordinated carbon in [CO4]4--groups. The [CO4]4--groups polymerize by corner-sharing to form pyramidal [C4O10]4--groups, which can bind three or four hydrogen atoms. As the pyramidal [C4O10]4--groups are a constituent of several anhydrous sp3-carbonates, we now expect that further high-pressure hydrous carbonates can be obtained.