Search

The high‐precision X‐ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X‐ray Free‐Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X‐ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X‐ray heating and diffraction of Bi under pressure, obtained using 20 fs X‐ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC. [ABSTRACT FROM AUTHOR]

Fast compression experiments performed using dynamic diamond anvil cells (dDACs) employing piezoactuators offer the opportunity to study compression-rate dependent phenomena. In this paper, we describe an experimental setup which allows us to perform time-resolved x-ray diffraction during the fast compression of materials using improved dDACs. The combination of the high flux available using a 25.6 keV x-ray beam focused with a linear array of compound refractive lenses and the two fast GaAs LAMBDA detectors available at the Extreme Conditions Beamline (P02.2) at PETRA III enables the collection of x-ray diffraction patterns at an effective repetition rate of up to 4 kHz. Compression rates of up to 160 TPa/s have been achieved during the compression of gold in a 2.5 ms fast compression using improved dDAC configurations with more powerful piezoactuators. The application of this setup to low-Z compounds at lower compression rates is described, and the high temporal resolution of the setup is demonstrated. The possibility of applying finely tuned pressure profiles opens opportunities for future research, such as using oscillations of the piezoactuator to mimic propagation of seismic waves in the Earth. [ABSTRACT FROM AUTHOR]

A detailed description is presented of the Extreme Conditions Beamline P02.2 for micro X-ray diffraction studies of matter at simultaneous high pressure and high/low temperatures at PETRA III, in Hamburg, Germany. This includes performance of the X-ray optics and instrumental resolution as well as an overview of the different sample environments available for high-pressure studies in the diamond anvil cell. Particularly emphasized are the high-brilliance and high-energy X-ray diffraction capabilities of the beamline in conjunction with the use of fast area detectors to conduct time-resolved compression studies in the millisecond time regime. Finally, the current capability of the Extreme Conditions Science Infrastructure to support high-pressure research at the Extreme Conditions Beamline and other PETRA III beamlines is described. [ABSTRACT FROM AUTHOR]

Abstract: Using a newly developed experimental protocol based on externally heated diamond anvil cells, in situ stress and textures studies are performed on polycrystalline body-centered cubic-(α-), face-centered cubic-(γ-) and hexagonal close-packed-(ε-)Fe during plastic deformation up to 36GPa and 1000K. At 7GPa and 973K, α-Fe displays a texture attributed to dominant slip on . Upon pressure increase up to 24GPa at constant temperature, differential stress is shown to increase to 0.6±0.1GPa while Fe is transforming into γ-Fe and ε-Fe. Textures observed in γ-Fe are fully induced by phase transformation, with little effect of plastic deformation. Textures observed in ε-Fe are the result of phase transformation from γ-Fe combined with plastic deformation, with dominant basal slip. The differential stress measured in ε-Fe is consistent with a shear strength of ∼1.9GPa at 17GPa and 300K, with a temperature dependence of −0.003GPaK−1 and a pressure dependence of 0.074. [Copyright &y& Elsevier]

Vanadium has been reported to undergo phase transition upon compreßion from body-centered cubic (bcc) to rhombohedral structure around 62 GPa. In this paper we confirm the bcc to rhombohedral phase transition at 61.5 GPa under quasihydrostatic compreßion in the Ne preßure medium. Under the nonhydrostatic condition we find the phase transition occurring at 30 GPa at ambient temperature and 37 GPa at 425 K. We find the transition under the hydrostatic condition is hindered and it can occur at much lower preßure under the nonhydrostatic condition. [ABSTRACT FROM AUTHOR]

Dendritic cells (DCs) play a central role in antiviral immunity. Conflicting data on DC function have been reported for hepatitis C virus (HCV) infection. In addition to antigen presentation and cytokine secretion, a subset of human DCs displays direct cytotoxic activity. It has been suggested that measles virus and human immunodeficiency virus (HIV) may enhance cytotoxicity of DCs potentially leading to apoptosis of activated T cells and subsequent down-regulation of antiviral immune responses. We demonstrate that CD1c-positive myeloid DCs, but not BDCA-4-positive plasmacytoid DCs, are able to kill different target cells mainly via tumour necrosis factor-related apoptosis-inducing ligand. The ability of CD1c+ DCs to lyze target cells was found to be completely impaired in patients with chronic hepatitis C (10 chronic HCV patients vs 10 healthy controls; P < 0.001) but not in patients with primary biliary cirrhosis. Successful antiviral therapy of chronic hepatitis C rescued the cytotoxicity of DCs. Myeloid DCs of HCV patients and healthy controls had a similar phenotype and endocytotic activity, however, the frequency of mDCs in the peripheral blood was lower ( P = 0.004) and the allostimulatory function was weaker ( P < 0.001) in chronic hepatitis C. Thus, in contrast to HIV and measles virus studies on monocyte-derived DCs, freshly isolated myeloid DCs of patients with hepatitis C do not show an increased but a completely abolished cytotoxic activity. The impaired DC cytotoxicity could represent a novel mechanism for the increased prevalence of autoimmunity in HCV infection. [ABSTRACT FROM AUTHOR]

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti3Si0.5Ge0.5C2 sample. Up to a pressure of 53 GPa, no phase transformations were observed. As for the isostructural hexagonal Ti3SiC2, the compressibility along the c axis was greater than along a. The bulk modulus is 183±4 GPa with a pressure derivative of 3.4±0.2. This work shows that the replacement of Si by Ge in Ti3SiC2 results in a systematic decrease in the bulk moduli. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

As-cast amorphous AsSe (a-AsSe) has been characterized by in-situ high pressure XRD and Raman spectroscopy up to the pressure of ~30GPa using diamond anvil cell together with ab-initio molecular dynamics simulations. A gradual densification has been observed under compression along with the breakdown of intermediate range ordering at ~16GPa. The whole transformation process can be divided into three relatively distinct pressure regimes from 1 bar to 7GPa, from 7 to 16GPa, and beyond 16GPa. Our XRD results together with Raman spectroscopic studies confirm that in the a-AsSe pressure tuning results in network transformations only, without sudden jump in the density. The results obtained by high pressure ab-initio molecular dynamics simulations demonstrate the variations in the local structures associated with the experimentally observed transformations. The amorphous-to-amorphous network transformation is found to be reversible upon decompression. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the laboratory study of extreme conditions of temperature and density, the exposure of matter to high intensity radiation sources has been of central importance. Here, we interrogate the performance of multi-layered targets in experiments involving high intensity, hard x-ray irradiation, motivated by the advent of extremely high brightness hard x-ray sources, such as free electron lasers and 4th-generation synchrotron facilities. Intense hard x-ray beams can deliver significant energy in targets having thick x-ray transparent layers (tampers) around samples of interest for the study of novel states of matter and materials' dynamics. Heated-state lifetimes in such targets can approach the microsecond level, regardless of radiation pulse duration, enabling the exploration of conditions of local thermal and thermodynamic equilibrium at extreme temperature in solid density matter. The thermal and mechanical responses of such thick layered targets following x-ray heating, including hydrodynamic relaxation and heat flow on picosecond to millisecond timescales, are modeled using radiation hydrocode simulation, finite element analysis, and thermodynamic calculations. Assessing the potential for target survival over one or more exposures and resistance to damage arising from heating and resulting mechanical stresses, this study doubles as an investigation into the performance of diamond anvil high pressure cells under high x-ray fluences. Long used in conjunction with synchrotron x-ray radiation and high power optical lasers, the strong confinement afforded by such cells suggests novel applications at emerging high intensity x-ray facilities and new routes to studying thermodynamic equilibrium states of warm, very dense matter. [ABSTRACT FROM AUTHOR]

We have performed in situ synchrotron X-ray diffraction experiments on TaC0.99 compressed in a diamond anvil cell along 3 isothermal paths to maximum pressure (P)-temperature (T) conditions of 38.8 GPa at 1073 K. By combining measurements performed in axial diffraction geometry at 296 K and in radial geometry at 673 K and 1073 K, we place constraints on the pressure-volume-temperature (P-V-T) equation of state of TaC in a wide range of conditions. A fit of the Birch-Murnaghan equation to the measurements performed in axial geometry at ambient temperature yields a value of the isothermal bulk modulus at ambient conditions K T 0 = 305 ± 5 (1 σ) GPa and its pressure derivative (∂ K T / ∂ P) T 0 = 6.1 ± 0.5. The fit of the Birch-Murnaghan-Debye model to our complete P-V-T dataset allows us to constrain the Grüneisen parameter at ambient pressure γ 0 = V (∂ P / ∂ E) V 0 to the value of 1.2 ± 0.1. [ABSTRACT FROM AUTHOR]

The structural evolution of a liquid GaIn eutectic alloy under high temperature and high pressure is investigated by combining in situ X-ray diffraction (XRD) and ab initio molecular dynamics simulations. Both experimental and theoretical results confirm that no pressure-induced sudden structural changes are detected in the liquid state along different isotherms below 700 K. The XRD patterns indicate that the liquids at 400 and 673 K both crystallize into a tetragonal crystalline phase under high pressure, whose structure is locally face centered cubic (fcc)-like. The theoretical simulations successfully describe the atomic-scale structural evolution from disordered liquid to ordered solid phases during the isothermal compression at different temperatures, revealing a strong competition between the body-centered cubic (bcc)-like and fcc-like local atomic packings at the early stage of nucleation. The liquid can directly solidify into the bcc-like atomic packing at temperatures above 650 K, whereas this bcc-like structure becomes transient and metastable below 600 K and finally transforms into a stable fcc-like atomic packing with increasing pressure. Furthermore, a high-pressure and high-temperature "phase diagram" of the GaIn eutectic alloy is roughly constructed, providing new insight into atomic-scale disorder-to-order transition of the liquid GaIn eutectic alloy in extreme conditions. [ABSTRACT FROM AUTHOR]

The elastic bulk modulus softening of (Mg,Fe)O ferropericlase across the iron spin crossover induces dramatic changes in its physical properties, including seismic P‐velocities and viscosity. Here, we performed compression of powders of (Mg0.8‐0.9Fe0.2‐0.1)O in a piezo‐driven dynamic Diamond Anvil Cell (dDAC) and derive the bulk modulus by differentiation of pressure and volume data, providing first data on the broadness of the elastic softening for ferropericlase with mantle‐relevant compositions. We complement our experimental results with theoretical calculations that extend previous studies by considering multiple random configurations of iron, and going beyond treating high‐ and low‐spin iron as an ideal solution. Both experiments and computations show a broad and asymmetric softening of the bulk modulus, and suggest that the softening is sensitive to the distribution of iron in the ferropericlase structure. Our high‐temperature calculations show that mixed‐spin (Mg,Fe)O dominates the lower mantle at all depths below 1,000 km. In contrast to most previous works, we find that ferropericlase will not exist in pure low‐spin state along a typical mantle geotherm. Based on our model, the physical properties of ferropericlase will show significant lateral variation at depths below 1,400 km, with the strongest effects expected between 2,000 and 2,600 km. Plain Language Summary: Understanding the physical properties of deep mantle minerals is pivotal to interpret geophysical observables and constrain large‐scale geodynamic models. (Mg,Fe)O ferropericlase is the second most abundant mineral in Earth's lower mantle, ranging from 660 to 2,890 km depths. Previous works have shown that the electronic configuration of iron in ferropericlase changes at pressures corresponding to the mid‐mantle. This process, called iron‐spin crossover, markedly affects a variety of physical properties, including seismic wave speeds and viscosity. Here we combine novel experiments and theoretical calculations to provide a coherent picture of the onset depth and broadness of the spin crossover in Earth's lower mantle. We show that the spin crossover happens throughout most of the lower mantle, altering physical properties at most depths up to the core‐mantle boundary. This quantitative understanding is key to model the impacts of the spin crossover on geophysical mantle properties and mantle dynamics. Key Points: We constrain the broadness of the iron spin crossover by a combination of novel experiments and computationsWe find a broad and asymmetric spin crossover range, which is sensitive to the distribution of iron in the ferropericlase structureFerropericlase is in mixed‐spin state throughout the lower mantle, but shows lateral spin state variations, impacting on mantle properties [ABSTRACT FROM AUTHOR]

Scientific tasks aimed at decoding and characterizing complex systems and processes at high pressures set new challenges for modern X-ray diffraction instrumentation in terms of X-ray flux, focal spot size and sample positioning. Presented here are new developments at the Extreme Conditions beamline (P02.2, PETRA III, DESY, Germany) that enable considerable improvements in data collection at very high pressures and small scattering volumes. In particular, the focusing of the X-ray beam to the sub-micrometer level is described, and control of the aberrations of the focusing compound refractive lenses is made possible with the implementation of a correcting phase plate. This device provides a significant enhancement of the signal-to-noise ratio by conditioning the beam shape profile at the focal spot. A new sample alignment system with a small sphere of confusion enables single-crystal data collection from grains of micrometer to sub-micrometer dimensions subjected to pressures as high as 200 GPa. The combination of the technical development of the optical path and the sample alignment system contributes to research and gives benefits on various levels, including rapid and accurate diffraction mapping of samples with sub-micrometer resolution at multimegabar pressures. [ABSTRACT FROM AUTHOR]

The ability to visualize a sample undergoing a pressure-induced phase transition allows for the determination of kinetic parameters, such as the nucleation and growth rates of the high-pressure phase. For samples that are opaque to visible light (such as metallic systems), it is necessary to rely on x-ray imaging methods for sample visualization. Here, we present an experimental platform developed at beamline P02.2 at the PETRA III synchrotron radiation source, which is capable of performing simultaneous x-ray imaging and diffraction of samples that are dynamically compressed in piezo-driven diamond anvil cells. This setup utilizes a partially coherent monochromatic x-ray beam to perform lensless phase contrast imaging, which can be carried out using either a parallel- or focused-beam configuration. The capabilities of this platform are illustrated by experiments on dynamically compressed Ga and Ar. Melting and solidification were identified based on the observation of solid/liquid phase boundaries in the x-ray images and corresponding changes in the x-ray diffraction patterns collected during the transition, with significant edge enhancement observed in the x-ray images collected using the focused-beam. These results highlight the suitability of this technique for a variety of purposes, including melt curve determination. [ABSTRACT FROM AUTHOR]

The stability of high-entropy alloys (HEAs) is a key issue before their selection for industrial applications. In this study, in-situ high-pressure and high-temperature synchrotron radiation X-ray diffraction experiments have been performed on three typical HEAs Ni20Co20Fe20Mn20Cr20, Hf25Nb25Zr25Ti25, and Re25Ru25Co25Fe25 (at. %), having face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close-packed (hcp) crystal structures, respectively, up to the pressure of ~80 GPa and temperature of ~1262 K. Under the extreme conditions of the pressure and temperature, all three studied HEAs remain stable up to the maximum pressure and temperatures achieved. For these three types of studied HEAs, the pressure-dependence of the volume can be well described with the third order Birch-Murnaghan equation of state. The bulk modulus and its pressure derivative are found to be 88.3 GPa and 4 for bcc-Hf25Nb25Zr25Ti25, 193.9 GPa and 5.9 for fcc-Ni20Co20Fe20Mn20Cr20, and 304.6 GPa and 3.8 for hcp-Re25Ru25Co25Fe25 HEAs, respectively. The thermal expansion coefficient for the three studied HEAs is found to be in the order as follows: fcc-Ni20Co20Fe20Mn20Cr20>bcc-Hf25Nb25Zr25Ti25 ≈hcp-Re25Ru25Co25Fe25. [ABSTRACT FROM AUTHOR]

Background With the withdrawal of aprotinin from worldwide marketing in November 2007, many institutions treating patients at high risk for hyperfibrinolysis had to update their therapeutic protocols. At our institution, the standard was switched from aprotinin to ɛ-aminocaproic acid (EACA) in all patients undergoing cardiac surgery with extracorporeal circulation including neonates. Although both antifibrinolytic medications have been used widely for many years, there are few data directly comparing their blood-sparing effect and their side-effects especially in neonates. Methods Perioperative data from 235 neonates aged up to 30 days undergoing primary cardiac surgery were analysed. Between July 1, 2006 and November 5, 2007, all patients (n=95) received aprotinin. Starting November 6, 2007 until December 31, 2009, all patients (n=140) were treated with EACA. The primary outcome criterion was blood loss; secondary outcome criteria were transfusion requirements, renal, vascular, and neurological complications and also in-hospital mortality. Results All descriptive and intraoperative data variable were similar. Blood loss was significantly higher in the EACA group (P=0.001), but there was no difference in the rate of re-operation for bleeding (P=0.218) nor the number of transfusions. There were no differences in the incidences of postoperative renal, neurological, and vascular events or in-hospital mortality. Conclusions In neonatal patients undergoing cardiac surgery, the switch to EACA treatment led to a higher postoperative blood loss. However, there were no differences in transfusion requirements or major clinical outcomes. [ABSTRACT FROM AUTHOR]

Using a synchrotron-radiation source and a diamond-anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Zr2InC sample. Up to a pressure of 52 GPa, no phase transformations were observed. As observed in Ti3SiC2 and Ti3Si0.5Ge0.5C2, the compressibility of Zr2InC along the c axis was greater than along the a axis. The bulk modulus is 127±5 GPa, with a pressure derivative of 4.25±0.3; the former is in excellent agreement with our ab initio calculations (130.9 GPa). The a (3.367 Å) and c (15.100 Å) parameters from the ab initio calculations are also slightly larger than those measured here, viz., 3.35 and 14.91 Å. Surprisingly, a hysteresis was observed in the a-lattice parameters; they were higher upon unloading than loading. The reason for this hysteresis is not clear at this time. [ABSTRACT FROM AUTHOR]

A resistively-heated dynamic diamond anvil cell (RHdDAC) setup is presented. The setup enables the dynamic compression of samples at high temperatures by employing a piezoelectric actuator for pressure control and internal heaters for high temperature. The RHdDAC facilitates the precise control of compression rates and was tested in compression experiments at temperatures up to 1400 K and pressures of ∼130 GPa. The mechanical stability of metallic glass gaskets composed of a FeSiB alloy was examined under simultaneous high-pressure/high-temperature conditions. High-temperature dynamic compression experiments on H2O ice and (Mg, Fe)O ferropericlase were performed in combination with time-resolved x-ray diffraction measurements to characterize crystal structures and compression behaviors. The employment of high brilliance synchrotron radiation combined with two fast GaAs LAMBDA detectors available at the Extreme Conditions Beamline (P02.2) at PETRA III (DESY) facilitates the collection of data with excellent pressure resolution. The pressure–temperature conditions achievable with the RHdDAC combined with its ability to cover a wide range of compression rates and perform tailored compression paths offers perspectives for a variety of future experiments under extreme conditions. [ABSTRACT FROM AUTHOR]

We present an improved setup for the experimental study of deformation of solids at simultaneous high pressures and temperatures by radial x-ray diffraction. This technique employs a graphite resistive heated Mao–Bell type diamond anvil cell for radial x-ray diffraction in combination with a water-cooled vacuum chamber. The new chamber has been developed by the sample environment group at PETRA III and implemented at the Extreme Conditions Beamline P02.2 at PETRA III, DESY (Hamburg, Germany). We discuss applications of the new setup to study deformation of a variety of materials, including ferropericlase, calcium perovskite, bridgmanite, and tantalum carbide, at high-pressure/temperature. [ABSTRACT FROM AUTHOR]

We performed high-pressure synchrotron x-ray diffraction experiments on nanocrystalline (nc-) MgO compressed both under quasi-hydrostatic and non-hydrostatic conditions in a diamond-anvil cell. Data obtained under hydrostatic conditions show that nc-MgO (average crystallite size of 20 nm) is 8-9% more compressible than 'bulk' MgO. Analysis of our results collected under non-hydrostatic conditions yields a bulk modulus that is about 27% larger than the one derived from the quasi-hydrostatic compression experiments. Thus, the apparent bulk modulus strongly depends on the experimental stress conditions. [ABSTRACT FROM AUTHOR]

High pressure angle-dispersive X-ray diffraction investigations have been carried out on α-cristobalite form of Al0.5Ga0.5PO4. Our investigations show that the structural stability of this phase under high pressure depends on the nature of pressure conditions in the diamond anvil cell. Under hydrostatic pressure conditions using neon as a pressure transmitting medium, ambient orthorhombic C2221 phase transforms to orthorhombic Cmcm phase at 4.9 GPa. The high pressure Cmcm phase remains stable up to the highest pressure in the experiment, i.e. 19 GPa. The values of bulk modulus for C2221 and Cmcm phases are 19(2) and 126(4) GPa, respectively. In contrast to this, under non-hydrostatic pressure conditions, transformation of ambient C2221 phase to Cmcm phase has not observed up to 17.4 GPa. Instead, a new monoclinic phase P21 is observed which contains layers of six coordinated Al/Ga ions separated by less dense five coordinated Al/Ga ions. [ABSTRACT FROM AUTHOR]

Abstract: We experimentally determined the bulk modulus of (Mg0.8Fe0.2)O ferropericlase across the iron spin transition and in the low‐spin phase by employing a new experimental approach. In our measurements, we simulate the propagation of a compressional seismic wave (P wave) through our sample by employing a piezo‐driven dynamic diamond anvil cell that allows to oscillate pressure at seismic frequencies. During pressure oscillations, X‐ray diffraction images were continuously collected every 5–50 ms. The bulk modulus is directly calculated from these data at different pressures. Our experiments show a pronounced softening of the bulk modulus throughout the spin crossover, supporting previous single‐crystal measurements at very high frequencies and computations. Comparison of our results to previous data collected on (Mg,Fe)O with lower iron contents shows that the magnitude of softening strongly depends on iron content. Our experiments at seismic frequencies confirm that the iron spin crossover markedly affects the ratio of seismic compressional to shear wave velocities in Earth's lower mantle. [ABSTRACT FROM AUTHOR]

Seismic anisotropy in Earth's lowermost mantle, resulting from Crystallographic Preferred Orientation (CPO) of elastically anisotropic minerals, is among the most promising observables to map mantle flow patterns. A quantitative interpretation, however, is hampered by the limited understanding of CPO development in lower mantle minerals at simultaneously high pressures and temperatures. Here, we experimentally determine CPO formation in ferropericlase, one of the elastically most anisotropic deep mantle phases, at pressures of the lower mantle and temperatures of up to 1400 K using a novel experimental setup. Our data reveal a significant contribution of slip on {100} to ferropericlase CPO in the deep lower mantle, contradicting previous inferences based on experimental work at lower mantle pressures but room temperature. We use our results along with a geodynamic model to show that deformed ferropericlase produces strong shear wave anisotropy in the lowermost mantle, where horizontally polarized shear waves are faster than vertically polarized shear waves, consistent with seismic observations. We find that ferropericlase alone can produce the observed seismic shear wave splitting in D″ in regions of downwelling, which may be further enhanced by post-perovskite. Our model further shows that the interplay between ferropericlase (causing V SH > V SV ) and bridgmanite (causing V SV > V SH ) CPO can produce a more complex anisotropy patterns as observed in regions of upwelling at the margin of the African Large Low Shear Velocity Province. [ABSTRACT FROM AUTHOR]

The crystal structure and vibration spectra of sodium niobate NaNbO3have been studied by means of neutron diffraction, X-ray diffraction and Raman spectroscopy at high pressures. An isostructural phase transformation from the initial antiferroelectric phase to an intermediate antiferroelectric phase HP-I have been observed under 2 GPa. This transformation is caused by complex reorientations of NbO6octahedra. Subsequent structural phase transition from the phase HP-I to an orthorhombic phase HP-III have been detected at pressures above 10 GPa. This transition leads to suppression of an antiferroelectric state of NaNbO3. The observed phase transitions are accompanied by anomalies in lattice parameters compression. [ABSTRACT FROM PUBLISHER]

The structural and magnetic properties of Cr 2 O 3 have been studied by means of X-ray and neutron powder diffraction at high pressures up to 35 GPa. The lattice compression of the rhombohedral crystal structure of R 3 ¯ c symmetry is slightly anisotropic with anomaly in the pressure behavior of the c/a parameters ratio at P ≈ 20 GPa of presumably magnetic nature. The oxygen octahedra around chromium ions become more symmetric with close values of shared and unshared bonds under high pressure. The antiferromagnetic structure of Cr 2 O 3 remains stable in the studied pressure range up to 35 GPa. The pressure coefficient of the Néel temperature, (1/ T N )( dT N /dP ) = + 0.0091 GPa −1 , is significantly less in comparison with perovskite-like compounds containing Cr 3+ and Mn 4+ ions of similar electronic configuration. [ABSTRACT FROM AUTHOR]

We have investigated the high-pressure structural and vibrational behavior of the ordered kesterite-type Cu2ZnSnS4 compound. Our investigations have revealed two structural transitions: a kesterite-to-disordered kesterite transition was observed between 7 and 9 GPa, which involves a Zn/Cu disorder within the respective cationic sublattice, whereas a rocksalt-type structure was realized at ∼15 GPa. The latter transition is accompanied by a cationic coordination increase from fourfold-to-sixfold with respect to the sulfur anions. The predicted kesterite-to-stannite transition was not detected. Furthermore, our high-pressure Raman studies have shown that the aforementioned Zn/Cu cationic disorder will always be present in Cu2ZnSnS4 under relatively moderate compression. [ABSTRACT FROM AUTHOR]

The monazite-type solid solution La 1 − x Pr x PO 4 was synthesized by solid-state reaction and extensively investigated using electron microprobe and thermogravimetric analyses, differential scanning and high-temperature oxide melt solution calorimetry, powder X-ray diffraction, infrared and Raman spectroscopy. Lattice parameters and Ln -O bond lengths show a decrease with increasing Pr content. A small excess volume is observed for the solid solution. IR spectra of the solid solution members present no detectable differences, while a blue shift of the PO 4 -related modes is seen in the Raman data. This shift can be attributed to the lanthanide contraction. Within errors, calorimetry data show no systematic deviation from an ideal behavior, though one might interpret the data as an indication of a slightly asymmetric mixture. All data indicate that deviations from ideality of the solid solution – if present – are very small. [ABSTRACT FROM AUTHOR]

The crystal, magnetic structure and vibrational spectra of multiferroic GaFeO 3 have been studied by means of neutron, X-ray powder diffraction and Raman spectroscopy at pressures up to 6.2 and 42 GPa, respectively. A presence of Fe/Ga antisite disorder leads to a formation of the ferrimagnetic ground state with the Néel temperature T N = 292 K at ambient pressure. Upon compression, the magnetic ground state symmetry remains the same and the Néel temperature increases with a pressure coefficient (1/T N )(dT N /dP) = 0.011(1) GPa −1 . Application of high pressure above 21 GPa leads to a gradual structural phase transition from the polar orthorhombic Pc 2 1 n phase to nonpolar orthorhombic Pbnm phase. It is accompanied by anomalies in the pressure behaviour of several Raman modes. Pressure dependencies of lattice parameters and Raman modes frequencies in the observed structural phases were obtained. [ABSTRACT FROM AUTHOR]

Metallic osmium (Os) is one of the most exceptional elemental materials, having, at ambient pressure, the highest known density and one of the highest cohesive energies and melting temperatures. It is also very incompressible, but its high-pressure behaviour is not well understood because it has been studied so far only at pressures below 75 gigapascals. Here we report powder X-ray diffraction measurements on Os at multi-megabar pressures using both conventional and double-stage diamond anvil cells, with accurate pressure determination ensured by first obtaining self-consistent equations of state of gold, platinum, and tungsten in static experiments up to 500 gigapascals. These measurements allow us to show that Os retains its hexagonal close-packed structure upon compression to over 770 gigapascals. But although its molar volume monotonically decreases with pressure, the unit cell parameter ratio of Os exhibits anomalies at approximately 150 gigapascals and 440 gigapascals. Dynamical mean-field theory calculations suggest that the former anomaly is a signature of the topological change of the Fermi surface for valence electrons. However, the anomaly at 440 gigapascals might be related to an electronic transition associated with pressure-induced interactions between core electrons. The ability to affect the core electrons under static high-pressure experimental conditions, even for incompressible metals such as Os, opens up opportunities to search for new states of matter under extreme compression. [ABSTRACT FROM AUTHOR]

The melting of bismuth in response to shock compression has been studied using in situ femtosecond x-ray diffraction at an x-ray free electron laser. Both solid-solid and solid-liquid phase transitions are documented using changes in discrete diffraction peaks and the emergence of broad, liquid scattering upon release from shock pressures up to 14 GPa. The transformation from the solid state to the liquid is found to occur in less than 3 ns, very much faster than previously believed. These results are the first quantitative measurements of a liquid material obtained on shock release using x-ray diffraction, and provide an upper limit for the time scale of melting of bismuth under shock loading. [ABSTRACT FROM AUTHOR]

Between 19 and 54 GPa, potassium has a complex composite incommensurate host-guest structure which undergoes two intraphase transitions over this pressure range. The temperature dependence of these host-guest phases is further complicated by the onset of an order-disorder transition in their guest chains. Here, we report single-crystal, quasi-single-crystal, and powder synchrotron x-ray diffraction measurements of this order-disorder phenomenon in incommensurate potassium to 47 GPa and 750 K. The so-called chain melting transition is clearly visible over a 22 GPa pressure range, and there are significant changes in the slope of the phase boundary which divides the ordered and disordered phases, one of which results from the intraphase transitions in the guest structure. [ABSTRACT FROM AUTHOR]

High pressure x-ray powder-diffraction experiments were performed on europium metal up to ~70 GPa. Above 38 GPa, europium transforms from the incommensurately modulated Eu-IV phase to a second phase with an incommensurately modulated crystal structure, Eu-V. This is a previously unseen incommensurately modulated to incommensurately modulated transition in the elements at high pressure. High-pressure high-temperature experiments were also performed up to 449 K in order to make an initial estimate of the positions of the phase boundaries of the incommensurate phases. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structures of anion-deficit cobaltite LaBaCoO have been studied by the X-ray and neutron diffraction methods at high pressures up to 30 and 6 GPa, respectively. A structure transition from the cubic phase with symmetry $Pm\bar 3m$ to the tetragonal phase with symmetry P4/ mmm has been observed in this compound at P ≈ 3 GPa. It is accompanied by the change of the ground antiferromagnetic state of the G type to the ferromagnetic state because of a change in the electronic configuration of Co ions. Possible mechanisms of the observed magnetic phase transition, as well as the role of the superexchange interactions between Co ions in various spin states in the formation of magnetic properties, have been discussed. Pressure-induced change in the magnetic state of LaBaCoO significantly differs from related stoichiometric compounds LaACoO (A = Sr, Ca), where the ground ferromagnetic state is formed and the sign of the pressure dependence of the Curie temperature depends on the element A. [ABSTRACT FROM AUTHOR]

Modifications of structural arrangements including relaxation processes were investigated in swift-heavy-ion-bombarded Fe 73 Cu 1 Nb 3 Si 16 B 7 metallic glass. The irradiation of as-quenched amorphous ribbons was accomplished with 3 MeV u −1 (u is atomic mass unit) and 11.1 MeV u −1 Au ions with total fluences of up to 1 × 10 13 ions cm −2 . Specimens irradiated with 3 MeV u −1 ions were subsequently annealed for 4 h at 350 °C. Ion-irradiated samples including those heat-treated were studied using in situ temperature-dependent diffraction of high-energy X-ray synchrotron radiation (wavelength of 0.020689 nm). Cyclic heating–cooling regimes were applied during the measurements. A tendency towards a higher degree of disorder was revealed as a function of the ion fluence in both types of alloys. During the first heating–cooling cycle, a remarkable hysteresis is observed in the position and line width of the first diffraction peak, especially in the as-quenched irradiated alloys. The hysteresis increases with rising ion fluence but vanishes completely after the first heating–cooling cycle. No hysteresis is found in the irradiated and subsequently annealed alloys. The irradiation-induced structural modifications have some features similar to the effects caused by mechanical deformation. [ABSTRACT FROM AUTHOR]

Recent advances in storage ring technology pioneered by MAX IV (Sweden) allow synchrotron radiation sources to achieve significantly smaller emittances than those currently in operation. This new, multi-bend achromat technology can thus boost spectral brightness, enabling unprecedented experimental possibilities. The high-energy synchrotron radiation facilities ESRF (France), SPring-8 (Japan), and APS (USA) have settled upgrade plans to improve their storage ring emittance by up to two orders of magnitude at 6 GeV electron energy. PETRA III at DESY has the largest circumference with 2.3 km. As the emittance scales favorably with the storage ring size, an upgrade of PETRA III offers the unique potential to reach a diffraction limit up to X-ray energies of 10 keV. Operating at 6 GeV with an emittance of 10 pmrad, this PETRA IV facility would pave the way for new experimental opportunities, especially for those using high photon energies. [ABSTRACT FROM AUTHOR]

The behavior of a natural topaz, AlSiO(OHF), has been investigated by means of in situ single-crystal synchrotron X-ray diffraction up to 45 GPa. No phase transition or change in the compressional regime has been observed within the pressure-range investigated. The compressional behavior was described with a third-order Birch-Murnaghan equation of state (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are as follows: K = 158(4) GPa and K ′ = 3.3(3). The confidence ellipse at 68.3 % (Δχ = 2.30, 1σ) was calculated starting from the variance-covariance matrix of K and K′ obtained from the III-BM-EoS least-square procedure. The ellipse is elongated with a negative slope, indicating a negative correlation of the parameters K and K ′, with K = 158 ± 6 GPa and K ′ = 3.3 ± 4. A linearized III-BM-EoS was used to obtain the axial-EoS parameters (at room- P), yielding: K( a) = 146(5) GPa [ β = 1/(3 K( a)) = 0.00228(6) GPa] and K′( a) = 4.6(3) for the a-axis; K( b) = 220(4) GPa [ β = 0.00152(4) GPa] and K′( b) = 2.6(3) for the b-axis; K( c) = 132(4) GPa [ β = 0.00252(7) GPa] and K′( c) = 3.3(3) for the c-axis. The elastic anisotropy of topaz at room- P can be expressed as: K( a): K( b): K( c) = 1.10:1.67:1.00 ( β: β: β = 1.50:1.00:1.66). A series of structure refinements have been performed based on the intensity data collected at high pressure, showing that the P-induced structure evolution at the atomic scale is mainly represented by polyhedral compression along with inter-polyhedral tilting. A comparative analysis of the elastic behavior and P/ T-stability of topaz polymorphs and 'phase egg' (i.e., AlSiOOH) is carried out. [ABSTRACT FROM AUTHOR]

The structural, magnetic, and vibrational properties of PbFe0.5Nb0.5O3 relaxor multiferroic have been studied by means of x-ray, neutron powder diffraction, and Raman spectroscopy at pressures up to 30 GPa. Two successive structural phase transitions from the initial R3m polar phase to Cm and Pm monoclinic polar phases were observed at P = 5.5 and 8.5 GPa. Both transitions are associated with anomalies in pressure behavior of several stretching and bending modes of oxygen octahedra as well as Fe/Nb localized vibrational modes. The G-type antiferromagnetic order remains stable upon compression up to 6.4 GPa, assuming possible multiferroic properties of pressure-induced phases. The Neel temperature increases with a pressure coefficient (1 /TN)dTN/dP = 0.012 GPa-1. The observed pressure-induced phenomena in PbFe0.5Nb0.5O3 are in drastic contrast with conventional multiferroics, exhibiting a general tendency towards a suppression of polar phases and/or magnetoelectric coupling under pressure. [ABSTRACT FROM AUTHOR]

The high-pressure behavior of LiLaNbO ( x = 1/6, 1/3, 1/2, 2/3) perovskites where Li cations were substituted for the existing vacancies was studied using synchrotron X-ray diffraction. It was shown that all these materials undergo irreversible pressure-induced amorphization around 14.5 GPa regardless of the Li concentration. The Li-inserted materials were found to exhibit a standard pressure response (bulk modulus pressure derivative B′ ~4) when in the crystalline phase, whereas LaNbO shows a linear volume contraction versus pressure, i.e., B′ ~(−1). These results suggest that the structural collapse is not a consequence of cation disorder resulting from the Nb atoms (B-site) migrating to the A-site vacancies. The observed pressure response can be understood by increased occupancy of the A-sites opposing the tilting of the NbO octahedra. The pressure evolution of the Nb oxidation state is discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dc conductivity is Arrhenius-like with activation energy in the range 0.73−0.84eV. [•] Relative static permittivity ranges from 9.6 up to 12.8. [•] At 1000wt.-ppm Ho, modular diagrams are semicircular and independent of temperature. [•] At 2000wt.-ppm Ho, two relaxation processes appear and crystallization takes place. [•] High Ho doping shortens inter-atomic distances and enhances mean atomic density. [ABSTRACT FROM AUTHOR]

We report on an x-ray diffraction (XRD) study of helical poly[9,9-bis(2-ethylhexyl)fluorene] (PF2/6) under high quasihydrostatic pressure and show an effect of pressure on the torsion angle (dihedral angle) between adjunct repeat units and on the hexagonal unit cell. A model for helical backbone conformation is constructed. The theoretical position for the most prominent 001 x-ray reflection is calculated as a function of torsion angle. The XRD of high molecular weight PF2/6 (Ma = 30 kg/mol) is measured through a diamond anvil cell upon pressure increase from 1 to 10 GPa. The theoretically considered 001 reflection is experimentally identified, and its shift with the increasing pressure is found to be consistent with the decreasing torsion angle between 2 and 6 GPa. This indicates partial backbone planarization towards a more open helical structure. The h00 peak is identified, and its shift together with the broadening of 00l implies impairment of the ambient hexagonal order, which begins at or below 2 GPa. Previously collected high-pressure photoluminescence data are reanalyzed and are found to be qualitatively consistent with the XRD data. This paper provides an example of how the helical 7r-conjugated backbone structure can be controlled by applying high quasihydrostatic pressure without modifications in its chemical structure. Moreover, it paves the way for wider use of high-pressure x-ray scattering in the research of Π-conjugated polymers. [ABSTRACT FROM AUTHOR]

The structural, magnetic, and vibrational properties of RbFe(MoO4)2 have been studied by means of x-ray and neutron powder diffraction, magnetic susceptibility measurements, and Raman spectroscopy at pressures up to 10 GPa. The gradual structural phase transition from the initial trigonal P3m1 phase to the monoclinic C2/c phase via the intermediate P3 phase was observed at P ∼ GPa. The triangular antiferromagnetic order with a propagation vector q = (1/3, 1/3, qz) in the suppressed trigonal phase remains incommensurate, and the qz value increases from 0.45 to 0.48 in the pressure range 0-2 GPa at T = 2 K. The pressure coefficient of the Néel temperature is equal to (1/TN)dTN/dP = 0.09 GPa-1. No evidence of the formation of the long-range magnetic order in the monoclinic phase was found. The pressure dependencies of the vibrational modes for the trigonal and monoclinic phases were obtained. [ABSTRACT FROM AUTHOR]

Data on partitioning behavior of elements between different phases at in situ conditions are crucial for the understanding of element mobility especially for geochemical studies. Here, we present results of in situ partitioning of trace elements (Zr, Pd, and Ru) between silicate and iron melts, up to 50 GPa and 4200 K, using a modified laser heated diamond anvil cell (DAC). This new experimental set up allows simultaneous collection of x-ray fluorescence (XRF) and x-ray diffraction (XRD) data as a function of time using the high pressure beamline ID27 (ESRF, France). The technique enables the simultaneous detection of sample melting based to the appearance of diffuse scattering in the XRD pattern, characteristic of the structure factor of liquids, and measurements of elemental partitioning of the sample using XRF, before, during and after laser heating in the DAC. We were able to detect elements concentrations as low as a few ppm level (2-5 ppm) on standard solutions. In situ measurements are complimented by mapping of the chemical partitions of the trace elements after laser heating on the quenched samples to constrain the partitioning data. Our first results indicate a strong partitioning of Pd and Ru into the metallic phase, while Zr remains clearly incompatible with iron. This novel approach extends the pressure and temperature range of partitioning experiments derived from quenched samples from the large volume presses and could bring new insight to the early history of Earth. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the behavior of the structure of titanium hydride (TiH2), an important compound in hydrogen storage research, at elevated temperatures (0–120°C) and high pressures (1bar–34GPa). Temperature-induced changes of TiH2 as indicated in the alteration of the ambient X-ray demonstrated a cubic to tetragonal phase transition occurring at about 17°C. The main focus of this study was to identify any pressure-induced structural transformations, including possible phase transitions, in TiH2. Synchrotron X-ray diffraction studies were carried out in situ (diamond anvil cell) in a compression sequence up to 34GPa and in subsequent decompression to ambient pressure. The pressure evolution of the diffraction patterns revealed a cubic (Fm-3m) to tetragonal (I4/mmm) phase transition at 2.2GPa. The high-pressure phase persisted up to 34GPa. After decompression to ambient conditions the observed phase transition was completely reversible. A Birch–Murnaghan fit of the unit cell volume as a function of pressure yielded a zero-pressure bulk modulus K 0=146(14)GPa, and its pressure derivative K′0=6(1) for the high-pressure tetragonal phase of TiH2. [Copyright &y& Elsevier]

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe2O3 and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mössbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory+dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites. [ABSTRACT FROM AUTHOR]

Observations of multiferroicity and giant improper ferroelectricity in CaMn7O12 invigorated the research on this material. Delicate structural changes have been reported to cause ferroelectricity in the magnetically ordered state of CaMn7O12 as well as high-temperature crystallographic transformations. Through high-resolution synchrotron x-ray diffraction experiments we show for the first time the large negative thermal expansion (NTE) behavior of the cubic phase of CaMn7O12. A large NTE coefficient αL for a temperature window of around 60 K is inferred for the cubic phase in the phase coexistence region during the high-temperature structural transition. It is explained using quasirigid unit modes. We also observe a large phase coexistence region of about 100 K across the high-temperature first-order structural transition, which is different from previous reports. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of multiferroic CuO have been studied by means of neutron and x-ray powder diffraction at pressures up to 11 and 38 GPa, respectively, and by first-principles theoretical calculations. Anomalous lattice compression is observed, with enlargement of the lattice parameter a, reaching a maximum at P=13GPa, followed by its reduction at higher pressures. The lattice distortion of the monoclinic structure at high pressures is accompanied by a progressive change of the oxygen coordination around Cu atoms from the square fourfold towards the octahedral sixfold coordination. The pressure-induced evolution of the structural properties and electronic structure of CuO was successfully elucidated in the framework of full-electronic density functional theory calculations with range-separated HSE06, and meta-generalized gradient approximation hybrid M06 functionals. The antiferromagnetic (AFM) ground state with a propagation vector q=(0.5,0,-0.5) remains stable in the studied pressure range. From the obtained structural parameters, the pressure dependencies of the principal superexchange magnetic interactions were analyzed, and the pressure behavior of the Néel temperature as well as the magnetic transition temperature from the intermediate incommensurate AFM multiferroic state to the commensurate AFM ground state were evaluated. The estimated upper limit of the Néel temperature at P=38GPa is about 260 K, not supporting the previously predicted existence of the multiferroic phase at room temperature and high pressure. [ABSTRACT FROM AUTHOR]

In pressure-induced reversible structural transitions, the term "reversible" refers to the recovery of the virgin structure in a material upon complete decompression. Pressure-induced amorphous-to-crystalline transitions have been claimed to be reversible, but evidence that amorphous material recovers its virgin amorphous structure upon complete depressurization has been lacking. In amorphous As2Se3 (a-As2Se3) chalcogenide, however, we report a novel reversible amorphous-to-crystalline transition that provides compelling experimental evidence that upon complete decompression, the recovered amorphous phase is structurally the same as that of the virgin (as-cast) amorphous phase. Combining the experimental results with ab initio molecular dynamics simulations, we elucidate that the amorphization is mediated by a surplus of total free energy in the high-pressure face-centered cubic phase as compared to the virgin amorphous phase and that the structural recovery to the virgin amorphous phase is a consequence of an enhancement in covalent bonding character over interlayer forces upon complete decompression. Furthermore, we observed a two-dimensional to three-dimensional network transition under compression and its reversibility upon decompression. [ABSTRACT FROM AUTHOR]

Despite the intensive studies for decades, it is still not well understood how qualitatively different magnetic behaviors can occur in a narrow composition range for the Fe-rich Fe-transition metal (TM) amorphous alloys. In this study of amorphous Fe100-xZrx (x=7, 9, 12) metallic glasses, normal ferromagnetism (FM) is found at 12 % Zr where only the FM-paramagnetic (PM) transition is observed at the Curie temperature, TC. In contrast, spin-glass (SG)-PM transition at a temperature, Tg, called SG temperature, is only observed at 7 % Zr, while in the transient re-entrant composition range (x=8-11), an SG-FM transition at a temperature, Tf, called spin-freezing temperature, is also observed at low temperature besides the normal FM-PM transition at TC. In order to understand this unusual behavior, a detailed characterization of pressure (atomic volume), composition, and temperature dependence of the magnetic properties is coupled with high pressure synchrotron x-ray diffraction determination of the pressure dependence of the atomic volume. The results on Fe100-xZrx (x=7, 9, 12) are compared to those obtained for the FM Co91Zr9 metallic glass not showing any kind of anomalous magnetic properties. It is confirmed that the unusual behavior is caused by a granularlike magnetic structure where weakly coupled magnetic clusters are embedded into a FM bulk matrix. Since the mechanism of the magnetization reversal was found to be of the curling type rather than homogeneous rotation, the energy barrier determining the blocking temperature of the clusters is calculated as AR, where A is the exchange constant and R is the cluster size, in contrast to the usual characterization of the energy barrier by KV where K is the anisotropy energy and V is the cluster volume. The volume fraction of the FM part is a fast changing function of the bulk composition: Almost 100% FM fraction is found at 12% of Zr while no trace of real FM is observed at 7 at % Zr. The driving force of this surprising magnetic character is the atomic volume: The lower the Zr content, the higher is the fraction of Fe atoms with compressed atomic volume having low magnetic moment. The percolation of their network separates the clusters from the FM bulk. The complex magnetic behavior of the Fe-rich Fe-Zr amorphous system at low temperatures can thus be interpreted with the only assumption of a cluster-size distribution and a weak coupling of the clusters to the FM matrix. The introduction of this coupling is able to explain the opposite pressure dependence of Tg and Tf. The threshold atomic volume in the low magnetic moment regions is found to be comparable to the atomic volume characteristic to the low-spin limit of the face-centered-cubic Fe alloys. The extensive literature results on the anomalous magnetism for various Fe-rich Fe-TM amorphous alloys and especially for the Fe-rich Fe-Zr glassy system are also found to be in agreement with this granular magnetic behavior. [ABSTRACT FROM AUTHOR]