Seismic velocities of CaSiO3 perovskite can explain LLSVPs in Earth's lower mantle.

Seismology records the presence of various heterogeneities throughout the lower mantle1,2, but the origins of these signals-whether thermal or chemical-remain uncertain, and therefore much of the information that they hold about the nature of the deep Earth is obscured. Accurate interpretation of observed seismic velocities requires knowledge of the seismic properties of all of Earth's possible mineral components. Calcium silicate (CaSiO3) perovskite is believed to be the third most abundant mineral throughout the lower mantle. Here we simultaneously measure the crystal structure and the shear-wave and compressional-wave velocities of samples of CaSiO3 perovskite, and provide direct constraints on the adiabatic bulk and shear moduli of this material. We observe that incorporation of titanium into CaSiO3 perovskite stabilizes the tetragonal structure at higher temperatures, and that the material's shear modulus is substantially lower than is predicted by computations3-5 or thermodynamic datasets6. When combined with literature data and extrapolated, our results suggest that subducted oceanic crust will be visible as low-seismic-velocity anomalies throughout the lower mantle. In particular, we show that large low-shear-velocity provinces (LLSVPs) are consistent with moderate enrichment of recycled oceanic crust, and mid-mantle discontinuities can be explained by a tetragonal-cubic phase transition in Ti-bearing CaSiO3 perovskite.

Hyper-expanded interlayer separations in superconducting barium intercalates of FeSe.

Intercalation of Ba in ß-FeSe by ammonothermal synthesis results in the formation of different superconducting phases with interlayer distance ranging between 8.4 and 13.1 Å. The values of Tc are primarily dependent on Ba content, and are further modulated by the interlayer spacing through facile intercalation and deintercalation of ammonia.

Role of disorder in the thermodynamics and atomic dynamics of glasses.

We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higher-density crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal.

Importance of correlation effects in hcp iron revealed by a pressure-induced electronic topological transition.

We discover that hcp phases of Fe and Fe(0.9)Ni(0.1) undergo an electronic topological transition at pressures of about 40 GPa. This topological change of the Fermi surface manifests itself through anomalous behavior of the Debye sound velocity, c/a lattice parameter ratio, and Mössbauer center shift observed in our experiments. First-principles simulations within the dynamic mean field approach demonstrate that the transition is induced by many-electron effects. It is absent in one-electron calculations and represents a clear signature of correlation effects in hcp Fe.

A 30 T pulsed magnet with conical bore for synchrotron powder diffraction.

We report on the design, construction, and operation of a horizontal field, 30 T magnet system with a conical bore optimized for synchrotron x-ray powder diffraction. The magnet offers ±31° optical access downstream of the sample, which allows to measure a sufficiently large number of Debye rings for an accurate crystal structure analysis. Combined with a 290 kJ generator, magnetic field pulses of 60 ms length were generated in the magnet, with a rise time of 4.1 ms and a repetition rate of 6 pulses/h at 30 T. The coil is mounted inside a liquid nitrogen bath. A liquid helium flow cryostat reaches into the coil and allows sample temperature between 5 and 250 K. The setup was used on the European Synchrotron Radiation Facility beamlines ID20 and ID06.

Portable double-sided laser-heating system for Mössbauer spectroscopy and X-ray diffraction experiments at synchrotron facilities with diamond anvil cells.

The diamond anvil cell (DAC) technique coupled with laser heating is a major method for studying materials statically at multimegabar pressures and at high temperatures. Recent progress in experimental techniques, especially in high-pressure single crystal X-ray diffraction, requires portable laser heating systems which are able to heat and move the DAC during data collection. We have developed a double-sided laser heating system for DACs which can be mounted within a rather small (~0.1 m(2)) area and has a weight of ~12 kg. The system is easily transferable between different in-house or synchrotron facilities and can be assembled and set up within a few hours. The system was successfully tested at the High Pressure Station of White Beam (ID09a) and Nuclear Resonance (ID18) beamlines of the European Synchrotron Radiation Facility. We demonstrate examples of application of the system to a single crystal X-ray diffraction investigation of (Mg(0.87),Fe(3+) (0.09),Fe(2+) (0.04))(Si(0.89),Al(0.11))O(3) perovskite (ID09a) and a Synchrotron Mössbauer Source (SMS) study of (Mg(0.8)Fe(0.2))O ferropericlase (ID18).

Equivalence of the boson peak in glasses to the transverse acoustic van Hove singularity in crystals.

We compare the atomic dynamics of the glass to that of the relevant crystal. In the spectra of inelastic scattering, the boson peak of the glass appears higher than the transverse acoustic (TA) singularity of the crystal. However, the density of states shows that they have the same number of states. Increasing pressure causes the transformation of the boson peak of the glass towards the TA singularity of the crystal. Once corrected for the difference in the elastic medium, the boson peak matches the TA singularity in energy and height. This suggests the identical nature of the two features.

Absence of pressure-induced amorphization in LiKSO4.

Angle-resolved synchrotron radiation diffraction was used to investigate lithium potassium sulfate (LiKSO(4)) crystals under high pressure. We confirm that the title compound undergoes three phase transitions, α →ß, ß â†’ γ and γ →δ, observed at around 0.8 GPa, 4.0 GPa and 7.0 GPa, respectively. Two competitive structures are proposed for the ß-phase after powder diffraction data Rietveld refinements: an orthorhombic (space group Cmc 2(1)) or a monoclinic (space group Cc) structure. These structures correspond to the models of the low temperature phases. The γ-phase is indexed by a monoclinic structure. Finally, the δ-phase is found to be highly disordered. No evidence of any pressure-induced amorphous phase was observed up to 24 GPa, even under imposed highly non-hydrostatic conditions, contrary to previous propositions.

Symmetry breaking of ionic semiconductors under pressure: the case of InAs.

The NaCl-to-Cmcm phase transition and the Cmcm structure of InAs under high pressure are studied by x-ray diffraction. The lattice parameters and fractional coordinates are given as a function of pressure. We propose a mechanism responsible for this type of symmetry breaking under pressure. We show that the ppσ interactions do not play a major role in the stabilization of the NaCl structure. Consequently the NaCl-to-Cmcm transition occurs only in compounds with a large charge transfer. General conclusions on the behavior of III-V semiconductors under pressure are drawn.

High-pressure effect on PbTiO3: an investigation by Raman and x-ray scattering up to 63 GPa.

We report a room-temperature high-pressure x-ray and Raman scattering investigation of lead titanate (PbTiO3) up to 63 GPa. Three continuous phase transitions at 13, 20, and 45 GPa between tetragonal-like phases occur. As a result, no evidence is found for a pressure-induced morphotropic phase boundary. Our study provides experimental evidence that PbTiO3 presents a complex sequence of phases accommodating pressure through mechanisms involving oxygen octahedra tilting and reentrance of ferroelectricity.

Detection of adverse events in a Scottish hospital using a consensus-based methodology.

OBJECTIVE: To determine, using a consensus based methodology, the rate and nature of adverse events (AEs) among patients admitted to acute medicine, acute surgery and obstetrics in a large teaching hospital in Scotland. METHODS: Retrospective case-note review of 450 medical, nursing and medication records to identify and classify adverse events. For 354 patients whose length of stay was greater than 24 hours, the overall adverse event rate was 7.9% which ranged from 0% in obstetrics, 7.2% in acute medicine to 13% in acute surgery. Among all AEs, 43% were deemed preventable by a consensus group and 59% of the AEs contributed to a proportion of the patients' hospital stay or led to hospital readmission. Whilst nurse identification of adverse events was highly specific (94%), its sensitivity was poor (43%). Only 10% of the identified AEs were identified by the hospital's voluntary reporting system for adverse events. The estimated additional cost of adverse events in terms of bed days was l69,189 which if extrapolated Scotland-wide could cost l297 million per annum. CONCLUSIONS: This study supports the need to continue the traditional retrospective record review to identify adverse events. The current hospital-based reporting of adverse events does not provide a complete measure of adverse events and needs to be complemented by other measures.

Noblest of all metals is structurally unstable at high pressure.

In a series of experiments in externally electrically heated diamond anvil cells we demonstrate that at pressures above approximately 240 GPa gold adopts a hexagonal-close-packed structure. Ab initio calculations predict that at pressures about 250 GPa different stacking sequences of close-packed atomic layers in gold become virtually degenerate in energy, strongly supporting the experimental observations.

Effect of densification on the density of vibrational states of glasses.

We studied the effect of densification on the vibrational dynamics of a Na(2)FeSi(3)O(8) glass. The density of vibrational states (DOS) has been measured using nuclear inelastic scattering. The corresponding changes in the microscopic, intermediate-range, and macroscopic properties have also been investigated. The results reveal that, in the absence of local structure transformations, the Debye level and the glass-specific excess of vibrational states above it have the same dependence on density, and the evolution of the DOS is fully described by the transformation of the elastic medium.

Density of vibrational states of a hyperquenched glass.

The vibrational density of states of a hyperquenched and an annealed glass has been measured using nuclear inelastic scattering. The hyperquenched sample shows a higher number of vibrational states in the low-energy region with respect to the annealed glass. It reveals, however, lower density and sound velocity and, therefore, smaller Debye energy. After rescaling the energy axes in Debye energy units and area renormalization, the density of states of both samples becomes identical. Thus, the effect of quenching is described by the transformation of the continuous medium.

Novel behaviour and structure of new glasses of the type Ba-Al-O and Ba-Al-Ti-O produced by aerodynamic levitation and laser heating.

Novel barium aluminate (BaAl(2)O(4)) and barium alumino-titanate (BaAl(2)TiO(6)) glasses have been produced by aerodynamic levitation and laser heating. BaAl(2)O(4) forms a clear and colourless glass under containerless and rapid quenching conditions. Under similar rapid quenching conditions BaAl(2)TiO(6) forms an opaque and black glass, while under slower and controlled quenching conditions it is possible to form a clear and colourless glass. The formation of the opaque or clear glass is reversible and purely dependent on the quench rate used. By slowing the quench rate further, it is possible to produce a milky glass suggestive of liquid-liquid phase separation in the liquid before glassification. High-energy x-ray diffraction experiments confirm the glassy state of these materials and show coordination structures and bond distances similar to their crystalline analogues.

Beating the miscibility barrier between iron group elements and magnesium by high-pressure alloying.

Iron and magnesium are almost immiscible at ambient pressure. The low solubility of Mg in Fe is due to a very large size mismatch between the alloy components. However, the compressibility of Mg is much higher than that of Fe, and therefore the difference in atomic sizes between elements decreases dramatically with pressure. Based on the predictions of ab initio calculations, we demonstrate in a series of experiments in a multianvil apparatus and in electrically and laser-heated diamond anvil cells that high pressure promotes solubility of magnesium in iron. At the megabar pressure range, more than 10 at. % of Mg can dissolve in Fe and then the alloy can be quenched to ambient conditions. A generality of the concept of high-pressure alloying between immiscible elements is demonstrated by its application to two other Fe group elements, Co and Ni.

Rubberlike dynamics in sulphur above the lambda-transition temperature.

The high-frequency acoustic dynamics of sulfur across the liquid-liquid, lambda transition has been studied using inelastic x-ray scattering. The combination of these high-frequency data with lower frequency, literature data indicates that liquid sulfur develops, in the high-temperature, polymeric solution phase, some characteristic features of a rubber. In particular, entanglement coupling among polymeric chains plays a relevant role in the dynamics of this liquid phase.

Development of a new state-of-the-art beamline optimized for monochromatic single-crystal and powder X-ray diffraction under extreme conditions at the ESRF.

A new state-of-the art synchrotron beamline fully optimized for monochromatic X-ray diffraction at high pressure and high (or low) temperature is presented. In comparison with the old high-pressure beamline ID30, this new beamline exhibits outstanding performance in terms of photon flux and focusing capabilities. The main components of this new instrument will be described in detail and compared with the performance of beamline ID30. In particular, the choices in terms of X-ray source, X-ray optics, sample environment and detectors are discussed. The first results of the beamline commissioning are presented.

Nature of the first-order phase transition in fluid phosphorus at high temperature and pressure.

An in situ x-ray diffraction experiment has been performed on phosphorus to characterize the liquid-liquid transition which occurs at high temperature and pressure. The transition line has been measured over an extended temperature range up to 2200 degrees C at 0.3 GPa. From the shape of this line, a thermodynamic characterization of the transition is obtained in terms of latent heat and internal energy change. Moreover, the addition of the high-pressure high-temperature data to the known phase diagram of phosphorus allows us to conclude that this is a first-order transition between a dense molecular fluid and a polymeric liquid.

Iron-silica interaction at extreme conditions and the electrically conducting layer at the base of Earth's mantle.

The boundary between the Earth's metallic core and its silicate mantle is characterized by strong lateral heterogeneity and sharp changes in density, seismic wave velocities, electrical conductivity and chemical composition. To investigate the composition and properties of the lowermost mantle, an understanding of the chemical reactions that take place between liquid iron and the complex Mg-Fe-Si-Al-oxides of the Earth's lower mantle is first required. Here we present a study of the interaction between iron and silica (SiO2) in electrically and laser-heated diamond anvil cells. In a multianvil apparatus at pressures up to 140 GPa and temperatures over 3,800 K we simulate conditions down to the core-mantle boundary. At high temperature and pressures below 40 GPa, iron and silica react to form iron oxide and an iron-silicon alloy, with up to 5 wt% silicon. At pressures of 85-140 GPa, however, iron and SiO2 do not react and iron-silicon alloys dissociate into almost pure iron and a CsCl-structured (B2) FeSi compound. Our experiments suggest that a metallic silicon-rich B2 phase, produced at the core-mantle boundary (owing to reactions between iron and silicate), could accumulate at the boundary between the mantle and core and explain the anomalously high electrical conductivity of this region.