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Abstract Silicate and oxide glasses are often chemically doped with a variety of cations to tune for desirable properties in technological applications, but their performances are often limited by relatively lower mechanical and elastic properties. Finding a new route to synthesize silica-based glasses with high elastic and mechanical properties needs to be explored. Here, we report a dense SiO2-glass with ultra-high elastic moduli using sound velocity measurements by Brillouin scattering up to 72 GPa at 300 K. High-temperature measurements were performed up to 63 GPa at 750 K and 59 GPa at 1000 K. Compared to compression at 300 K, elevated temperature helps compressed SiO2-glass effectively overcome the kinetic barrier to undergo permanent densification with enhanced coordination number and connectivity. This hot compressed SiO2-glass exhibits a substantially high bulk modulus of 361–429 GPa which is at least 2–3 times greater than the metallic, oxide, and silicate glasses at ambient conditions. Its Poisson’s ratio, an indicator for the packing efficiency, is comparable to the metallic glasses. Even after temperature quench and decompression to ambient conditions, the SiO2-glass retains some of its unique properties at compression and possesses a Poisson’s ratio of 0.248(11). In addition to chemical alternatives in glass syntheses, coupled compression and heating treatments can be an effective means to enhance mechanical and elastic properties in high-performance glasses.

Thermal conductivity of Earth’s core affects Earth’s thermal structure, evolution and dynamics. Based on thermal conductivity measurements of iron–silicon alloys at high pressure and temperature conditions, the authors here propose Earth’s inner core could be older than previously expected.

The relation between antifungal susceptibility and treatment outcomes is not well-characterized. There is paucity of surveillance data for cerebrospinal fluid (CSF) isolates of cryptococcus investigated with YEASTONE colorimetric broth microdilution susceptibility testing. A retrospective study of laboratory-confirmed cryptococcus meningitis (CM) patients was conducted. The antifungal susceptibility of CSF isolates was determined using YEASTONE colorimetric broth microdilution. Clinical parameters, CSF laboratory indices, and antifungal susceptibility results were analyzed to identify risk factors for mortality. High rates of resistance to fluconazole and flucytosine were observed in this cohort. Voriconazole had the lowest MIC (0.06 µg/mL) and lowest rate of resistance (3.8%). In a univariate analysis, hematological malignancy, concurrent cryptococcemia, high Sequential Organ Failure Assessment (SOFA) score, low Glasgow coma scale (GCS) score, low CSF glucose level, high CSF cryptococcal antigen titer, and high serum cryptococcal antigen burden were associated with mortality. In a multivariate analysis, meningitis with concurrent cryptococcemia, GCS score, and high CSF cryptococcus burden, were independent predictors of poor prognosis. Both early and late mortality rates were not significantly different between CM wild type and non-wild type species.

Hydrogen-rich superhydrides are promising high-temperature superconductors which have been observed only at pressures above 170 GPa. Here the authors show that CeH9 can be synthesized at 80-100 GPa with laser heating, and is characterized by a clathrate structure with a dense 3-dimensional atomic hydrogen sublattice.

Executive Summary: Pneumonia is a leading cause of death worldwide, ranking third both globally and in Taiwan. This guideline was prepared by the 2017 Guidelines Recommendations for Evidence-based Antimicrobial agents use in Taiwan (GREAT) working group, formed under the auspices of the Infectious Diseases Society of Taiwan (IDST). A consensus meeting was held jointly by the IDST, Taiwan Society of Pulmonary and Critical Care Medicine (TSPCCM), the Medical Foundation in Memory of Dr. Deh-Lin Cheng, the Foundation of Professor Wei-Chuan Hsieh for Infectious Diseases Research and Education and CY Lee's Research Foundation for Pediatric Infectious Diseases and Vaccines. The final guideline was endorsed by the IDST and TSPCCM. The major differences between this guideline and the 2007 version include the following: the use of GRADE methodology for the evaluation of available evidence whenever applicable, the specific inclusion of healthcare-associated pneumonia as a category due to the unique medical system in Taiwan and inclusion of recommendations for treatment of pediatric pneumonia. This guideline includes the epidemiology and recommendations of antimicrobial treatment of community-acquired pneumonia, hospital-acquired pneumonia, ventilator-associated pneumonia, healthcare-associated pneumonia in adults and pediatric pneumonia. Keywords: Pneumonia, Guidelines, Treatment, Taiwan

Background/purpose: We reported an outbreak of Staphylococcus haemolyticus (SH) infection in a group of young patients (mean age 21.6) simultaneously hospitalized due to a mass-burn incident. This study analyzed the clinical features of these patients and the microbiological characteristics of the outbreak. Methods: All 50 patients hospitalized for burns were enrolled, and their clinical differences were analyzed based on culture results. A drug sensitivity test and pulsed-field gel electrophoresis (PFGE) were conducted to analyze the microbiological difference between SH isolates from the mass-burn casualty patients (the study group) and SH isolates from other patients hospitalized during the same period (the control group) with the intention of identifying the strain of SH outbreak. Results: Patients with isolated SH (N = 36) had a significantly higher disease severity (higher revised Baux score, APACHE II score, and concurrent bacteremia rate), and a significantly poorer clinical outcome (longer ICU and hospital stay, and longer MV usage). Significant differences in the phenotype (antibiotics drug sensitivity test) and genotype (PFGE typing) were observed between the study and control groups. The dominant PFGE type C identified among the study group was related to poorer outcomes in a subgroup analysis. Conclusion: A dominant PFGE type of SH infection was found in these mass-burn casualty patients. Pathogenesis or virulence factors may have contributed to our results. Further study of isolated SH should be conducted. Keywords: Burn, Outbreak, Outcome, Pulsed-field gel electrophoresis (PFGE), Staphylococcus haemolyticus (SH)

Background and purpose: Rapid identification of microbes in the bloodstream is crucial in managing septicemia because of its high disease severity, and direct identification from positive blood culture bottles through matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) can shorten the turnaround time. Therefore, we developed a simple method for rapid microbiological identification from positive blood cultures by using MALDI-TOF MS. Methods: We modified previously developed methods to propose a faster, simpler and more economical method, which includes centrifugation and hemolysis. Specifically, our method comprises two-stage centrifugation with gravitational acceleration (g) at 600g and 3000g, followed by the addition of a lysis buffer and another 3000g centrifugation. Results: In total, 324 monomicrobial bacterial cultures were identified. The success rate of species identification was 81.8%, which is comparable with other complex methods. The identification success rate was the highest for Gram-negative aerobes (85%), followed by Gram-positive aerobes (78.2%) and anaerobes (67%). The proposed method requires less than 10 min, costs less than US$0.2 per usage, and facilitates batch processing. Conclusion: We conclude that this method is feasible for clinical use in microbiology laboratories, and can serve as a reference for treatments or further complementary diagnostic testing. Keywords: Blood culture, Direct identification, MALDI-TOF MS

Abstract A pressure-induced anomalous valence crossover without structural phase transition is observed in archetypal cubic YbCu5 based heavy Fermion systems. The Yb valence is found to decrease with increasing pressure, indicating a pressure-induced crossover from a localized 4f 13 state to the valence fluctuation regime, which is not expected for Yb systems with conventional c–f hybridization. This result further highlights the remarkable singularity of the valence behavior in compressed YbCu5-based compounds. The intermetallics Yb2Pd2Sn, which shows two quantum critical points (QCP) under pressure and has been proposed as a potential candidate for a reentrant Yb2+ state at high pressure, was also studied for comparison. In this compound, the Yb valence monotonically increases with pressure, disproving a scenario of a reentrant non-magnetic Yb2+ state at the second QCP.

Mid-gap defects: Carriers in a trap The temporal dynamics of photo-generated electrons and holes in MoSe2 trapped by defects are revealed. While transitional metal dichalcogenides have significant potential for optoelectronic applications, samples tend to contain defects such as vacancies and impurities, most of which affect carrier mobility by inducing mid-gap states, i.e. within the bandgap. Now a team led by Yaguo Wang from the University of Texas elucidates the role of defects in samples grown by chemical vapor deposition. Femtosecond pump probe spectroscopy reveals that such defects are prone to capture (within few picoseconds) and then release (at slightly longer timescales of hundreds of picoseconds) electrons and holes. Such dynamics are intrinsic to samples grown with this particular method and possibly linked to the oxygen-associated impurities introduced during growth. This knowledge is relevant to engineering the properties of 2D materials for optoelectronics applications.

The source of the anisotropic layer (D'' layer) at the bottom of the lower mantle remains unclear. Here, using high pressure and temperature experiments, the authors find that seismic anisotropy observed at the D'' layer is caused by 50% deformation of the minerals post-perovskite and ferropericlase.

Terrestrial basalts have a unique iron isotopic signature taken as fingerprints of core formation. Here, high pressure studies show that force constants of iron bonds increase with pressure similarly for silicate and metals suggesting interplanetary isotopic variability is not due to core formation.

Recently we are witnessing the boom of high-pressure science and technology from a small niche field to becoming a major dimension in physical sciences. One of the most important technological advances is the integration of synchrotron nanotechnology with the minute samples at ultrahigh pressures. Applications of high pressure have greatly enhanced our understanding of the electronic, phonon, and doping effects on the newly emerged graphene and related 2D layered materials. High pressure has created exotic stoichiometry even in common Group 17, 15, and 14 compounds and drastically altered the basic σ and π bonding of organic compounds. Differential pressure measurements enable us to study the rheology and flow of mantle minerals in solid state, thus quantitatively constraining the geodynamics. They also introduce a new approach to understand defect and plastic deformations of nano particles. These examples open new frontiers of high-pressure research.

Interest in studying power flow dynamics has grown in recent years, with new power flow diagnostics being developed at Sandia National Laboratories for the Z Pulsed Power Facility. Presently, the only power flow loads that have been studied are cylindrical static or imploding loads that are driven by synchronous short pulse (100 ns rise time). Presented is a design that utilizes the dynamic materials properties program’s stripline geometry in a high voltage pulsed shaped (asymmetric asynchronous) driving mode. This design has exhibited repeatable current loss with a large time-varying inductance that is well matched to the machine at pulse initialization but which triples to high inductance in 800 ns. Evidence is presented that plasma not captured in the magnetohydrodynamic approximation and ill represented by any of our existing predictive pulsed power codes is adversely affecting load current delivery. The authors believe this design could be of great interest to the experimental and modeling communities for studying power flow dynamics.

Earth’s inner core is predominantly composed of solid iron (Fe) and displays intriguing properties such as strong shear softening and an ultrahigh Poisson’s ratio. Insofar, physical mechanisms to explain these features coherently remain highly debated. Here, we have studied longitudinal and shear wave velocities of hcp-Fe (hexagonal close-packed iron) at relevant pressure–temperature conditions of the inner core using in situ shock experiments and machine learning molecular dynamics (MLMD) simulations. Our results demonstrate that the shear wave velocity of hcp-Fe along the Hugoniot in the premelting condition, defined as T/Tm (Tm: melting temperature of iron) above 0.96, is significantly reduced by ~30%, while Poisson’s ratio jumps to approximately 0.44. MLMD simulations at 230 to 330 GPa indicate that collective motion with fast diffusive atomic migration occurs in premelting hcp-Fe primarily along [100] or [010] crystallographic direction, contributing to its elastic softening and enhanced Poisson’s ratio. Our study reveals that hcp-Fe atoms can diffusively migrate to neighboring positions, forming open-loop and close-loop clusters in the inner core conditions. Hcp-Fe with collective motion at the inner core conditions is thus not an ideal solid previously believed. The premelting hcp-Fe with collective motion behaves like an extremely soft solid with an ultralow shear modulus and an ultrahigh Poisson’s ratio that are consistent with seismic observations of the region. Our findings indicate that premelting hcp-Fe with fast diffusive motion represents the underlying physical mechanism to help explain the unique seismic and geodynamic features of the inner core. [ABSTRACT FROM AUTHOR]

Light elements in Earth's core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron-electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ~100 to 110 Wm21K21 for liquid Fe-9Si near the topmost outer core. If Earth's core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core-mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core-mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core. [ABSTRACT FROM AUTHOR]

Determination of the full elastic constants (cij) of methane hydrates (MHs) at extreme pressuretemperature environments is essential to our understanding of the elastic, thermodynamic, and mechanical properties of methane in MH reservoirs on Earth and icy satellites in the solar system. Here, we have investigated the elastic properties of singe-crystal cubic MH-sI, hexagonal MH-III, and orthorhombic MH-III phases at high pressures in a diamond anvil cell. Brillouin light scattering measurements, together with complimentary equation of state (pressure-density) results from X-ray diffraction and methane site occupancies in MH from Raman spectroscopy, were used to derive elastic constants of MH-sI, MH-II, and MH-III phases at high pressures. Analysis of the elastic constants for MH-sI and MH-II showed intriguing similarities and differences between the phases' compressional wave velocity anisotropy and shear wave velocity anisotropy. Our results show that these high-pressure MH phases can exhibit distinct elastic, thermodynamic, and mechanical properties at relevant environments of their respective natural reservoirs. These results provide new insight into the determination of how much methane exists in MH reservoirs on Earth and on icy satellites elsewhere in the solar system and put constraints on the pressure and temperature conditions of their environment. [ABSTRACT FROM AUTHOR]

Lattice strength and structural phase transitions of gadolinium (Gd) were determined under nonhydrostatic compression up to 55 GPa using an angle-dispersive radial x-ray diffraction technique in a diamond-anvil cell at room temperature. Three new phases of fcc structure, dfcc structure, and new monoclinic structure were observed at 25 GPa, 34 GPa, and 53 GPa, respectively. The radial x-ray diffraction data yield a bulk modulus K0=36(1) GPa with its pressure derivate K0'=3.8(1) at the azimuthal angle between the diamond cell loading axis and the diffraction plane normal and diffraction plane ψ=54.7°. With K0' fixed at 4, the derived K0 is 34(1) GPa. In addition, analysis of diffraction data with lattice strain theory indicates that the ratio of differential stress to shear modulus (t/G) ranges from 0.011 to 0.014 at pressures of 12-55 GPa. Together with estimated high-pressure shear moduli, our results show that Gd can support a maximum differential stress of 0.41 GPa, while it starts to yield to plastic deformation at 16 GPa under uniaxial compression. The yield strength of Gd remains approximately a constant with increasing pressure, and reaches 0.46 GPa at 55 GPa. [ABSTRACT FROM AUTHOR]

Acoustic compressional and shear wave velocities (VP, VS) of anhydrous (AHRG) and hydrous rhyolitic glasses (HRG) containing 3.28 wt% (HRG-3) and 5.90 wt% (HRG-6) total water concentration (H[sub 2]O[sub t]) have been measured using Brillouin light scattering (BLS) spectroscopy up to 3 GPa in a diamond-anvil cell at ambient temperature. In addition, Fourier-transform infrared (FTIR) spectroscopy was used to measure the speciation of H2O in the glasses up to 3 GPa. At ambient pressure, HRG-3 contains 1.58 (6) wt% hydroxyl groups (OH-) and 1.70 (7) wt% molecular water (H2Om) while HRG-6 contains 1.67 (10) wt% OH- and 4.23 (17) wt% H2Om where the numbers in parentheses are ±1s. With increasing pressure, very little H2Om, if any, converts to OH- within uncertainties in hydrous rhyolitic glasses such that HRG-6 contains much more H2Om than HRG-3 at all experimental pressures. We observe a nonlinear relationship between high-pressure sound velocities and H2Ot, which is attributed to the distinct effects of each water species on acoustic velocities and elastic moduli of hydrous glasses. Near ambient pressure, depolymerization due to OH[sup -] reduces VS and G more than VP and KS. VP and KS in both anhydrous and hydrous glasses decrease with increasing pressure up to ~1-2 GPa before increasing with pressure. Above ~1-2 GPa, VP and KS in both hydrous glasses converge with those in AHRG. In particular, VP in HRG-6 crosses over and becomes higher than VP in AHRG. HRG-6 displays lower VS and G than HRG-3 near ambient pressure, but VS and G in these glasses converge above ~2 GPa. Our results show that hydrous rhyolitic glasses with ~2-4 wt% H2Om can be as incompressible as their anhydrous counterpart above ~1.5 GPa. The nonlinear effects of hydration on high-pressure acoustic velocities and elastic moduli of rhyolitic glasses observed here may provide some insight into the behavior of hydrous silicate melts in felsic magma chambers at depth. [ABSTRACT FROM AUTHOR]

Diopside is one of the most important end-members of clinopyroxene, which is an abundant mineral in upper-mantle petrologic models. The amount of clinopyroxene in upper-mantle pyrolite can be ~15 vol%, while pyroxenite can contain as high as ~60 vol% clinopyroxene. Knowing the elastic properties of the upper-mantle diopside at high pressure-temperature conditions is essential for constraining the chemical composition and interpreting seismic observations of region. Here we have measured the single-crystal elasticity of Fe-enriched diopside (Di80Hd20, Di-diopside, and Hd-hedenbergite; also called Fe-enriched clinopyroxene) at high-pressure conditions up to 18.5 GPa by using in situ Brillouin light-scattering spectroscopy (BLS) and synchrotron X-ray diffraction in a diamond-anvil cell. Our experimental results were used in evaluating the effects of pressure and Fe substitution on the full single-crystal elastic moduli across the Di-Hd solid-solution series to better understand the seismic velocity profiles of the upper mantle. Using the third- or fourth-order Eulerian finite-strain equations of state to model the elasticity data, the derived aggregate adiabatic bulk and shear moduli (KS0, G0) at ambient conditions were determined to be 117(2) and 70(1) GPa, respectively. The first- and second-pressure derivatives of bulk and shear moduli at 300 K were (∂KS/∂P)T = 5.0(2), (∂²KS/∂P²)[sub T] = -0.12(4) GPa-1 and (∂G/∂P)T = 1.72(9), (∂²G/∂P²)T = -0.05(2) GPa-1, respectively. A comparison of our results with previous studies on end-member diopside and hedenbergite in the literatures shows systematic linear correlations between the Fe composition and single-crystal elastic moduli. An addition of 20 mol% Fe in diopside increases KS0 by ~1.7% (~2 GPa) and reduces G0 by ~4.1% (~3 GPa), but has a negligible effect on the pressure derivatives of the bulk and shear moduli within experimental uncertainties. In addition, our modeling results show that substitution of 20 mol% Fe in diopside can reduce V[sub P] and V[sub S] by ~1.8% and ~3.5%, respectively, along both an expected normal mantle geotherm and a representative cold subducted slab geotherm. Furthermore, the modeling results show that the VP and VS profiles of Fe-enriched pyroxenite along the cold subducted slab geotherm are ~3.2% and ~2.5% lower than AK135 model at 400 km depth, respectively. Finally, we propose that the presence of Fe-enriched pyroxenite (including Fe-enriched clinopyroxene, Fe-enriched orthopyroxene, and Feenriched olivine), can be an effective mechanism to cause low-velocity anomalies in the upper mantle regions atop the 410 km discontinuity at cold subudcted slab conditions. [ABSTRACT FROM AUTHOR]

The melting curve of H2O has been measured by in situ Raman spectroscopy in an externally heated diamond anvil cell up to 22 GPa and 900 K. The Raman-active OH-stretching bands and the translational modes of H2O as well as optical observations are used to directly and reliably detect melting in ice VII. The observed melting temperatures are higher than previously reported x-ray measurements and significantly lower than recent laser-heating determinations. However, our results are in accord with earlier optical determinations. The frequencies and intensities of the OH-stretching peaks change significantly across the melting line while the translational mode disappears altogether in the liquid phase. The observed OH-stretching bands of liquid water at high pressure are very similar to those obtained in shock-wave Raman measurements. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In situ high P-T Raman spectra of solid CO2 up to 67 GPa and 1660 K have been measured, using a micro-optical spectroscopy system coupled with a Nd:YLF laser heating system in diamond anvil cells. A metallic foil was employed to efficiently absorb the incoming Nd:YLF laser and heat the sample. The average sample temperature was accurately determined by detailed balance from the anti-Stokes/Stokes ratio, and was compared to the temperature of the absorber determined by fitting the thermal radiation spectrum to the Planck radiation law. The transformation temperature threshold and the transformation dynamics from the molecular phases III and II to the polymeric phase V, previously investigated only by means of temperature quench experiments, was determined at different pressures. The P-T range of the transformation, between 640 and 1100 K in the 33–65 GPa pressure interval, was assessed to be a kinetic barrier rather than a phase boundary. These findings lead to a new interpretation of the high P-T phase diagram of carbon dioxide. Furthermore, our approach opens a new way to perform quantitative in situ Raman measurements under extremely high pressures and temperatures, providing unique information about phase relations and structural and thermodynamic properties of materials under these conditions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The pressure induced phase transformations in pure LiAlH4 were studied using in situ Raman spectroscopy. The analyses of the spectra reveal a phase transition at approximately 3 GPa from the ambient pressure monoclinic [alpha]-LiAlH4 phase to a high pressure phase [beta]-LiAlH4 having a distorted [[AlH4].sup.-] tetrahedron and the Al-H stretching mode in the quenched state further shifts to lower frequencies, suggesting a weakening of the Al-H bond.

The pressure dependence of the crystal and electronic structures of (NH3)yCs0.4FeSe, which has two pressure-induced superconducting domes of the SC1 and SC2 phases, was investigated by x-ray diffraction and emission spectroscopy at low temperatures. We found a pressure-induced change in the crystal structure from tetragonal (T) to collapsed tetragonal (cT) and peculiar pressure dependence of the magnetic moment between the SC1 and SC2 phases at a low temperature. The electronic structure also markedly changed between the two phases. The results suggest that the increase in the electron–electron correlation accompanying the increase in the magnetic moment may relate the high Tc in the SC2 phase. Theoretical calculations using the multi-orbital Hubbard model revealed that the spin susceptibility decreases in the SC1 phase and increases in the SC2 phase with the T → cT phase transition. [ABSTRACT FROM AUTHOR]

In this study, we measured the sound velocities of single-crystal periclase by Brillouin light scattering (BLS) combined with in situ synchrotron X-ray diffraction (XRD) up to ~30 GPa and 900 K in an externally heated diamond-anvil cell (EHDAC). Our experimental results were used to evaluate the combined effects of pressure and temperature on the elastic moduli of single-crystal periclase using third-order Eulerian finite-strain equations. All of the elastic moduli increased with increasing pressure but decreased with increasing temperature, except the off-diagonal modulus C12, which remained almost constant up to ~30 GPa and 900 K. The derived aggregate adiabatic bulk and shear moduli (KS0, G0) at ambient conditions were 162.8(±0.2) and 130.3(±0.2) GPa, respectively, consistent with literature results. The pressure derivatives of the bulk [(∂KS/∂P)300 K] and shear moduli [(∂G/∂P)300 K] at ambient conditions were 3.94(±0.05) and 2.17(±0.02), respectively, whereas the temperature derivatives of these moduli [(∂KS/∂T)P and (∂G/∂T) P]] at ambient conditions were -0.025(±0.001) and -0.020(±0.001) GPa/K, respectively. A comparison of our experimental results with the high-pressure (P) and high-temperature (T) elastic moduli of ferropericlase (Fp) in the literature showed that all the elastic moduli of Fp were linearly correlated with the FeO content up to approximately 20 mol%. These results allowed us to build a comprehensive thermoelastic model for Fp to evaluate the effect of Fe-Mg substitution on the elasticity and seismic parameters of Fp at the relevant P-T conditions of the lower mantle. Our modeling results showed that both the increase of the Fe content in Fp and the increasing depth could change the compressional wave anisotropy (AVP) and shear wave splitting anisotropy (AVS) of Fp in the upper parts of the lower mantle. Furthermore, using our modeling results here, we also evaluated the contribution of Fp to seismic lateral heterogeneities of thermal or chemical origin in the lower mantle. Both the thermally induced and Fe-induced heterogeneities ratios (RS/P = ∂lnVS/∂lnVP) of Fp from 670 to 1250 km along a representative lower mantle geotherm increased by ~2-5% and ~15%, respectively. The thermally induced RS/P value of Fp20 is ~30% higher than Fp10, indicating that the Fe content has a significant effect on the thermally induced RS/P of Fp. Compared to the seismic observation results (RS/P = 1.7-2.0) in the upper regions of the lower mantle, the Fe-induced RS/P value of Fp is more compatible than the thermally induced RS/P value of Fp20 (the expected composition of Fp in the lower mantle) within their uncertainties. Thus, we propose that Fe-induced lateral heterogeneities can significantly contribute to the observed seismic lateral heterogeneities in the Earth's lower mantle (670-1250 km). [ABSTRACT FROM AUTHOR]

Objectives: Staphylococcus lugdunensis, a species of CoNS, has become an important hospital pathogen because of increasing resistance to β-lactam antibiotics such as methicillin and oxacillin. Methicillin resistance is mainly due to the acquisition of the staphylococcal cassette chromosome (SCC) mec (SCCmec). Little is known about the structure of SCCmec in methicillin- or oxacillin-resistant CoNS.Methods: WGS was performed to determine the structure of SCCmec elements of two clinical S. lugdunensis isolates: CMUH-22 and CMUH-25.Results: These elements were found to be flanked by DRs and IRs with unique mosaic structures and a common integration site in the 3' end of the rlmH gene. The sequences of the regions located between rlmH and the ISSau4-like transposase genes of both elements were similar to those of SCCmec Vt of Staphylococcus aureus PM1. The SCCmec (type V, 5C2&4) of CMUH-25 harboured a novel ccrC complex and a C2-like mec complex in opposite orientations, similar to the type V SCCmec of S. aureus WIS. The sequences of the ccrA4B4 genes and J1 and J2 regions of CMUH-25 were similar to those of the SCC element of Staphylococcus haemolyticus NCTC 11042. In contrast, portions of the sequence of the J1 region of type Vt (5C2) SCCmec in strain CMUH-22 were highly similar to portions of those of Staphylococcus epidermidis RP62A and the composite SCCmec type V of S. aureus WAMRSA40.Conclusions: These observations suggest that the SCCmec elements of CMUH-25 and CMUH-22 evolved separately and assembled through different recombination events. [ABSTRACT FROM AUTHOR]

The concentrations of Fe, Al, and Ni and their distributions were determined for all known natural assemblages of ferropericlase (fPer) and bridgmanite (Bridg), coexisting as inclusions in deep-mantle diamonds from Brazil, Canada, Guinea, and South Australia. Based upon these data, it is likely that some areas within the deep lower mantle are iron-rich and differ markedly from a pyrolitic composition. In the lowermost lower mantle, Bridg is Al-rich and fPer is Ni-poor, witnessing the presence of a free metallic phase in the mineral-forming environment. The iron partitioning in the Bridg + fPer association … in juvenile diamond inclusions is as low as 0.1-0.2. During ascent of the diamonds with their inclusions to the surface, the … eventually increases to values of 0.4-0.5 and even as high as 0.7. The details of the element partitioning between natural Bridg and fPer in the lower mantle are as follows: iron in Bridg is ferrous Fe2+ in the A site, substituting for Mg2+; almost all iron in fPer is ferrous Fe2+; the share of ferric Fe3+ iron in fPer is Fe3+/ΣFe = 8-12 at %; iron concentrations in both Bridg and fPer increase with depth (pressure), reflecting the increasing Fe content in the lower part of the lower mantle, different from that of a pyrolitic model. Al in Bridg is mainly in the cation site B and partly in the cation site A, in both cases substituting for Si, Mg, and Fe with vacancy formation; and in the case of Al positioning into both B and A sites, a charge-balanced reaction occurs. The natural samples show very diverse … values and elemental distribution that cannot be simply explained by our current understanding on alumina dissolution in Bridg and the spin transition of Fe2+ in fPer. These major differences between experimental results and observations in natural samples demonstrate the complex, inhomogeneous iron speciation and chemistry in the lower mantle. [ABSTRACT FROM AUTHOR]

The article comments on a study on the use of a laser to generate conditions similar to those inside the cores of Earth-like exoplanets, which references a research paper by R. G. Kraus et al., published within the issue of "Science." Topics discussed include the crystallization of molten iron under extreme conditions, factors for habitability of exoplanets, and theory on the formation of Earth-like exoplanets.

Single-crystal elasticity of candidate minerals in the Earth's mantle, such as that of ferropericlase and bridgmanite, etc., is very important for understanding the seismic observations, geodynamic flow patterns, and testing geochemical and mineralogical models of the planet's deep interior. Determination of the full elastic tensor typically requires measuring both compressional and shear wave velocities (vP and vS) of the candidate single crystal as a function of crystallographic orientations at high pressures, but it has been a huge technical challenge obtaining vP at pressures above 25 GPa using Brillouin light scattering coupled with in a diamond-anvil cell due to the spectral overlap of the sample vP with the vS of the diamond window. In this study, we present a new method to derive the full elastic tensor (Cij) of single crystals using only measured vS of a given crystal platelet as a function of the azimuthal angle. Experimentally determined vP and vS results from Brillouin measurements for cubic periclase (MgO) and spinel (MgAl2O4), tetragonal stishovite (SiO2), and orthorhombic zoisite [Ca2Al3Si3O12(OH)] at ambient conditions are used as examples to demonstrate the application of our approach from theoretical analyses and experimental prospective. For high-symmetry cubic minerals, such as cubic MgO and spinel, a suitable crystallographic plane with small tradeoffs between any two Cij in vS is required for the method to work well such that the obtained Cij using measured vS velocities alone can be within 3% of the values derived from using both vS and vP. Our analyses show that the (-1,0.5,0.2) platelet for periclase and the (1,1,0) platelet for spinel are respective optimal orientations for applying our method. For lower symmetry minerals, such as tetragonal stishovite and orthorhombic zoisite, three crystallographic planes, that are orthogonal to each other and are tilted at least 20° from the principal crystallographic planes, can be used to provide reliable constraints on Cij using measured vS alone. We have extended this method to derive Cij of the (-1,0.5,0.2) platelet for periclase at pressures of 5.8 and 11.3 GPa, in a high-pressure diamond-anvil cell to demonstrate the usefulness of the approach in studying the elasticity of Earth's mantle minerals at relevant pressure-temperature conditions. Our proposed approach can be extended to all other crystal systems at high pressures to overcome the constant lack of experimental vP velocities at above 25 GPa, potentially providing new experimental and theoretical approaches in constraining the elastic tensor of the materials in the Earth's deep interior, which will be an effective strategy to solve one of the most relevant difficulties involved in the experimental study of the elastic properties (especially elastic anisotropy) of minerals of the lower mantle. [ABSTRACT FROM AUTHOR]

The presence of water in the Earth's deep mantle is an issue of increasing interest in the field of highpressure mineralogy. An important task for further advancing research in the field is to create homogeneous single crystals of candidate deep-mantle water-bearing minerals of 1 mm or larger in size, which is required for applying them for the time-of-flight (TOF) single-crystal Laue diffraction method with a third-generation neutron instrument. In this study, we perform several experiments to demonstrate an improved methodology for growing hydrous crystals of such large sizes at relevant transition zone and lower-mantle conditions via very slow cooling over a maximum period of 1 day. Successfully synthesized crystals using this methodology include dense hydrous magnesium silicate (DHMS) phase E, hydrous wadsleyite, hydrous ringwoodite, and bridgmanite (silicate perovskite). It is also demonstrated that these hydrous crystals can be grown from deuterium enriched starting materials in addition to those having a natural hydrogen isotope ratio. Magnitudes of chemical and crystallographic heterogeneities of the product crystals were characterized by comprehensive analysis of X-ray precession photography, single-crystal X-ray diffraction (SCXRD), field-emission scanning electron microscope (FE-SEM), electron probe microanalyzer (EPMA), secondary ion mass spectroscopy (SIMS), powder X-ray diffraction (PXRD), and TOF neutron powder diffraction (TOF-NPD). The product crystals were confirmed to be inclusion free and crystallographically homogeneous. Compositional and isotopic differences of major elements and hydrogen isotope abundances were lower than 1 and 3%, respectively, among intracrystals and intercrystals within each recovered sample capsule. Phase E crystals up to 600 µm in the largest dimension were grown at a constant temperature of 1100 °C kept for 3 h. Using a lattice parameter-to-temperature relation of phase E, the thermal gradient in the sample capsules for the phase E synthesis has been evaluated to be 20 °C/mm. Hydrous wadsleyite crystals up to 1100 µm in the largest dimension were grown at 1390 °C with a temperature reduction of 70 °C during heating for 10 h. Hydrous ringwoodite crystals up to 1000 µm in the largest dimension were grown at around 1400 °C with a temperature reduction of 110 °C during heating for 12 h. Bridgmanite crystals up to 600 µm in the largest dimension were grown at 1700 °C with a temperature reduction of 30 °C during heating for 12 h. A TOF single-crystal diffraction instrument has been successfully used for analyzing one of the hydrous wadsleyite crystals, which demonstrated that single crystals appropriate for their expected usage are created using the method proposed in the present study. [ABSTRACT FROM AUTHOR]

Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature. [ABSTRACT FROM AUTHOR]

Studying the velocity-density profiles of iron and iron-silicon alloy at high pressures and temperatures is critical for understanding the Earth's core as well as the interiors of other planetary bodies. Here we have investigated the compressional wave velocity (VP) and density (p) profiles of polycrystalline bcc-Fe and Fe0.85Si0.15 alloy (8 wt.% Si) using in situ high-energy resolution inelastic X-ray scattering (HERIX) and synchrotron X-ray diffraction spectroscopies in an externally-heated diamond anvil cell (EHDAC) up to 15 GPa and 700 K. Based on the measured velocity-density (VP-p) and velocity-pressure (VP-P) relations of bcc-Fe at simultaneous high pressure and temperature (P-T) conditions, our results show a strong VP reduction at elevated temperatures at a constant density. Comparison of the VP-p profiles between the bcc-Fe and bcc-Fe0.85Si0.15 alloy indicates that the alloying effect of additional 8 wt.% Si on the VP-p relationship of bcc-Fe is predominant via a constant density decrease of approximately 0.6 g/cm³ (7%). Compared with the literature velocity results for bcc and hcp Fe-Si alloys, the bcc-Fe and Fe-Si alloys exhibit higher VP than their hcp phase counterparts at the given bcc-hcp transition pressures. Our results here strongly support the notion that high temperature has a strong effect on the VP of Fe and that the VP-p profile of Fe can be affected by structural and magnetic transitions. Analyses on literature elastic constants of the bcc Fe-Si alloys, as a function of P-T and Si content, show that the bcc phase displays extremely high VP anisotropy of 16-30% and VS splitting anisotropy of 40-90% at high temperatures, while the addition of Si further enhances the anisotropy. Due to the extremely high elastic anisotropy of the bcc Fe-Si alloy, a certain portion of the bcc Fe-Si alloy with the lattice-preferred orientation may produce VP and VS anisotropies to potentially account for the observed seismic anisotropy in the inner core. [ABSTRACT FROM AUTHOR]

High-pressure synchrotron Mössbauer (SMS) and X-ray emission (XES) spectroscopic measurements were conducted to investigate the spin and valence states of iron in (Al,Fe)-bearing magnesium silicate glass (Mg0.79Fe0.10Al0.10Si0.96O3) up to 126 GPa and 300 K. By analyzing the Fe Kβ emission spectra using the integrated relative difference (IRD) method, which accounts for the spectral broadening effects, the derived total spin momentum (S) of the iron in the glass shows no observable changes with pressure within the experimental uncertainties. A two-doublet fitting model representing two diverse local iron atomic environments was used to satisfactorily simulate the high-pressure SMS spectra of iron in the glass. The doublet with an averaged quadrupole splitting (QS) value of 1.94(±0.25) mm/s and chemical shift (CS) of 1.02(±0.25) mm/s at ambient conditions was assigned to be high-spin Fe2+, whereas the second doublet with QS = 0.83(±0.25) mm/s and CS = 0.49(±0.25) mm/s was assigned to be high-spin Fe3+. Increasing pressure continuously elevates the QS of Fe2+ from ~2 mm/s at ambient pressure to 3.5 mm/s at 126 GPa, while Fe3+ only exhibits a slight increase in the QS to 1.34(±0.25) mm/s. Comparing with previous experimental and theoretical studies on the local geometries and hyperfine parameters of silicate glasses and minerals, we conclude that the occurrence of the extremely high QS of Fe2+ in our glass above ~40-50 GPa can be associated with the enhanced density and diverse distortions and geometries of the local Fe2+ environments. Our combined XES and SMS results show that both Fe2+ and Fe3+ ions in Al-bearing silicate remain in the high-spin state, rather than undergoing a spin-pairing transition as proposed previously. Assuming that the silicate glass results can be used as an analog for understanding silicate melts, our results here indicate that iron ions likely experience significant changes in the local environments yet remain overall in the high-spin state in silicate melts at the extreme pressure and temperature conditions of the deep mantle. [ABSTRACT FROM AUTHOR]

In situ synchrotron X-ray diffraction experiments on natural magnesiosiderite [(Mg0.35Fe0.65)CO3] were conducted using resistive and laser-heated diamond-anvil cells (DACs) up to 78 GPa and 1200 K. Based on thermal elastic modeling of the measured pressure-volume curves at given temperatures, we have derived thermal equation of state (EoS) parameters and the spin-crossover diagram of magnesiosiderite across the spin transition. These results show the spin crossover broadened and shifted toward higher pressures at elevated temperatures. Low-spin magnesiosiderite is 6% denser and 8% more incompressible than the high-spin phase at 1200 K and high pressures. Within the spin crossover from 53 to 63 GPa at 1200 K, magnesiosiderite exhibits anomalous thermal elastic behaviors, including a dramatic increase in the thermal expansion coefficient by a factor of 20 and a drop in the isothermal bulk modulus and the bulk sound velocity by approximately 75 and 50%, respectively. Compared with the end-member magnesite [MgCO3] at relevant pressure-temperature conditions of the subducted slabs, the high-spin magnesiosiderite with 65 mol% FeCO3 is approximately 21-23% denser and its unit-cell volume is 2^1% larger, whereas the low-spin state is 28-29% denser and 2% smaller than the end-member magnesite. Since ferromagnesite with 20 mol% of iron has been proposed to be a potential deep-carbon carrier, our results here indicate that the dense low-spin ferromagnesite can become more stable than high-spin ferromagnesite at pressures above approximately 50 GPa, providing a mechanism for (MgFe)-bearing carbonate to be a major carbon host in the deeper lower mantle. [ABSTRACT FROM AUTHOR]

Perovskite oxides ABO3 are important materials used as components in electronic devices. The highly compact crystal structure consists of a framework of corner-shared BO6 octahedra enclosing the A-site cations. Because of these structural features, forming a strong bond between A and B cations is highly unlikely and has not been reported in the literature. Here we report a pressure- induced first-order transition in PbRuO3 from a common orthorhombic phase (Pbnm) to an orthorhombic phase (Pbn21) at 32 GPa by using synchrotron X-ray diffraction. This transition has been further verified with resistivity measurements and Raman spectra under high pressure. In contrast to most well-studied perovskites under high pressure, the Pbn21 phase of PbRuO3 stabilized at high pressure is a polar perovskite. More interestingly, the Pbn21 phase has the most distorted octahedra and a shortest Pb–Ru bond length relative to the average Pb–Ru bond length that has ever been reported in a perovskite structure. We have also simulated the behavior of the PbRuO3 perovskite under high pressure by first principles calculations. The calculated critical pressure for the phase transition and evolution of lattice parameters under pressure match the experimental results quantitatively. Our calculations also reveal that the hybridization between a Ru:t2g orbital and an sp hybrid on Pb increases dramatically in the Pbnm phase under pressure. This pressure-induced change destabilizes the Pbnm phase to give a phase transition to the Pbn21 phase where electrons in the overlapping orbitals form bonding and antibonding states along the shortest Ru–Pb direction at P > Pc. 4. [ABSTRACT FROM AUTHOR]

The recent discovery of iron ferropnictide superconductors has received intensive concern in connection with magnetically involved superconductors. Prominent features of ferropnictide superconductors are becoming apparent: the parent compounds exhibit an antiferromagnetic ordered spin density wave (SDW) state, the magnetic-phase transition is always accompanied by a crystal structural transition, and superconductivity can be induced by suppressing the SDW phase via either chemical doping or applied external pressure to the parent state. These features generated considerable interest in the interplay between magnetism and structure in chemically doped samples, showing crystal structure transitions always precede or coincide with magnetic transition. Pressure-tuned transition, on the other hand, would be more straightforward to superconducting mechanism studies because there are no disorder effects caused by chemical doping; however, remarkably little is known about the interplay in the parent compounds under controlled pressure due to the experimental challenge of in situ measuring both of magnetic and crystal structure evolution at high pressure and low temperatures. Here we show from combined synchrotron Mössbauer and X-ray diffraction at high pressures that the magnetic ordering surprisingly precedes the structural transition at high pressures in the parent compound BaFe2As2, in sharp contrast to the chemical-doping case. The results can be well understood in terms of the spin fluctuations in the emerging nematic phase before the long-range magnetic order that sheds light on understanding how the parent compound evolves from a SDW state to a superconducting phase, a key scientific inquiry of iron-based superconductors. [ABSTRACT FROM AUTHOR]

The recent discovery of iron ferropnictide superconductors has received intensive concern in connection with magnetically involved superconductors. Prominent features of ferropnictide superconductors are becoming apparent: the parent compounds exhibit an antiferromagnetic ordered spin density wave (SDW) state, the magnetic-phase transition is always accompanied by a crystal structural transition, and superconductivity can be induced by suppressing the SDW phase via either chemical doping or applied external pressure to the parent state. These features generated considerable interest in the interplay between magnetism and structure in chemically doped samples, showing crystal structure transitions always precede or coincide with magnetic transition. Pressure-tuned transition, on the other hand, would be more straightforward to superconducting mechanism studies because there are no disorder effects caused by chemical doping; however, remarkably little is known about the interplay in the parent compounds under controlled pressure due to the experimental challenge of in situ measuring both of magnetic and crystal structure evolution at high pressure and low temperatures. Here we show from combined synchrotron Mössbauer and X-ray diffraction at high pressures that the magnetic ordering surprisingly precedes the structural transition at high pressures in the parent compound BaFe2As2, in sharp contrast to the chemical-doping case. The results can be well understood in terms of the spin fluctuations in the emerging nematic phase before the long-range magnetic order that sheds light on understanding how the parent compound evolves from a SDW state to a superconducting phase, a key scientific inquiry of iron-based superconductors. [ABSTRACT FROM AUTHOR]

Electronic spin transitions of iron in the Earth's mantle minerals are of great interest to deep-Earth researchers because their effects on the physical and chemical properties of mantle minerals can significantly affect our understanding of the properties of the deep planet. Here we have studied the electronic spin states of iron in ringwoodite (Mg0.75Fe0.25)2SiO4 using synchrotron Mössbauer spec-troscopy in a diamond-anvil cell up to 82 GPa. The starting samples were analyzed extensively using transmission and scanning electron microscopes to investigate nanoscale crystal chemistry and local iron distributions. Analyses of the synchrotron Mössbauer spectra at ambient conditions reveal two non-equivalent iron species, (Fe2+)1 and (Fe2+)2, which can be attributed to octahedral and tetrahedral sites in the cubic spinel structure, respectively. High-pressure Mössbauer measurements show the disappearance of the hyperfine quadrupole splitting (QS) of the Fe2+ ions in both sites at approximately 45-70 GPa, indicating an electronic high-spin (HS) to low-spin (LS) transition. The spin transition exhibits a continuous crossover nature over a pressure interval of ~25 GPa, and is reversible under decompression. Our results here provide the first experimental evidence for the occurrence of the spin transition in the spinel-structured ringwoodite, a mantle olivine polymorph, at high pressures. [ABSTRACT FROM AUTHOR]

Ferropericlase [(Mg,Fe)O] is one of the most abundant minerals of the earth's lower mantle. The high-spin (HS) to low-spin (LS) transition in the Fe2+ ions may dramatically alter the physical and chemical properties of (Mg,Fe)O in the deep mantle. To understand the effects of compression on the ground electronic state of iron, electronic and magnetic states of Fe2+ in (Mg0.75Fe0.25)O have been investigated using transmission and synchrotron Mössbauer spectroscopy at high pressures and low temperatures (down to 5 K). Our results show that the ground electronic state of Fe2+ at the critical pressure Pc of the spin transition close to T = 0 is governed by a quantum critical point (T = 0, P = Pc) at which the energy required for the fluctuation between HS and LS states is zero. Analysis of the data gives Pc = 55 GPa. Thermal excitation within the HS or LS states (T > 0 K) is expected to strongly influence the magnetic as well as physical properties of ferropericlase. Multielectron theoretical calculations show that the existence of the quantum critical point at temperatures approaching zero affects not only physical properties of ferropericlase at low temperatures but also its properties at P-T of the earth's lower mantle. [ABSTRACT FROM AUTHOR]

Compressional wave velocity-density (VP - p) relations of candidate Fe alloys at relevant pressure-temperature conditions of the Earth's core are critically needed to evaluate the composition, seismic signatures, and geodynamics of the planet's remotest region. Specifically, comparison between seismic VP - &rgr; profiles of the core and candidate Fe alloys provides first-order information on the amount and type of potential light elements--including H, C, O, Si, and/or S--needed to compensate the density deficit of the core. To address this issue, here we have surveyed and analyzed the literature results in conjunction with newly measured VP-p results of hexagonal closest- packed (hep) Fe and hcp-Fe0.85Si0.15 alloy using in situ highenergy resolution inelastic X-ray scattering and X-ray diffraction. The nature of the Fe-Si alloy where Si is readily soluble in Fe represents an ideal solid-solution case to better understand the lightelement alloying effects. Our results show that high temperature significantly decreases the VP of hcp-Fe at high pressures, and the Fe-Si alloy exhibits similar high-pressure VP - &rgr; behavior to hcp-Fe via a constant density offset. These VP-p data at a given temperature can be better described by an empirical power-law function with a concave behavior at higher densities than with a linear approximation. Our new datasets, together with literature results, allow us to build new VP - &rgr; models of Fe alloys in order to determine the chemical composition of the core. Our models show that the VP -p profile of Fe with 8 wt % Si at 6,000 Κ matches well with the Preliminary Reference Earth Model of the inner core. [ABSTRACT FROM AUTHOR]

The electronic spin and valence states of iron in lower-mantle silicate perovskite have been previously investigated at high pressures using various experimental and theoretical techniques. However, experimental results and their interpretation remain highly debated. Here we have studied a well-characterized silicate perovskite starting sample [(Mg0.9,Fe0.1)SiO3] in a chemically inert Ne pressure medium at pressures up to 120 GPa using synchrotron Mössbauer spectra. Analyses of the Mössbauer spectra explicitly show a high-spin to low-spin transition of the octahedral-site Fe3+ occurring at ~13--24 GPa, as evidenced from a significant increase in the hyperfine quadrupole splitting. Two quadrupole doublets of the A-site Fe2+, with extremely high-QS values of 4.1 and 3.1 mm/s, occur simultaneously with the spin transition of the octahedral-site Fe3+ and continue to develop to 120 GPa. It is conceivable that the spin-pairing transition of the octahedral-site Fe3+ causes a volume reduction and a change in the local atomic-site configurations that result in a significant increase of the quadrupole splitting in the dodecahedral-site Fe2+ at 13--24 GPa. Our results here provide a coherent explanation for recent experimental and theoretical results on the spin and valence states of iron in perovskite, and assist in comprehending the effects of the spin and valence states of iron on the properties of the lower-mantle minerals. [ABSTRACT FROM AUTHOR]

Ferromagnesite [(Mg,Fe)CO3] has been proposed as a candidate host mineral for carbon in the Earth's mantle. Studying its physical and chemical properties at relevant pressures and temperatures helps our understanding of deep-carbon storage in the planet's interior and on its surface. Here we have studied high-pressure vibrational and elastic properties of magnesian siderite [(Mg0.35Fe0.65)CO3] across the electronic spin transition by Raman and X-ray diffraction spectroscopies in a diamond-anvil cell. Our results show an increase in Raman shift of the observed lattice modes of magnesian siderite across the spin transition at 45 GPa as a result of an ~8% unit-cell volume collapse and a 10% stiffer lattice (higher bulk modulus). C-O bond lengthening in the strong, rigid (CO3)2- unit across the spin transition contributes to a competitive decrease in Raman shift, most evident in the Raman shift decrease of the symmetric stretching mode. Combined vibrational and elastic results are used to derive the mode Grüneisen parameter of each mode, which drops significantly across the transition. These results suggest that the low-spin state has distinctive vibrational and elastic properties compared to the high-spin state. Analyses of all recent experimental results on the (Mg,Fe)CO3 system show no appreciable compositional effect on the transition pressure, indicating weak iron-iron exchange interactions. Our results provide new insight into understanding the effects of the spin transition on the vibrational, elastic, and thermodynamic properties of (Mg,Fe)CO3 as a candidate carbon-host in the deep mantle. [ABSTRACT FROM AUTHOR]

High-pressure phonon density of states (PDOS) of Fe2O3 across structural and electronic transitions has been investigated by nuclear resonant inelastic x-ray scattering (NRIXS) and first-principles calculations together with synchrotron Mössbauer, x-ray diffraction, and x-ray emission spectroscopies. Drastic changes in elastic, thermodynamic, and vibrational properties of Fe2O3 occur across the Rh2O3(II)-type structural transition at 40-50 GPa, whereas the Mott insulator-metal transition occurring after the structural transition only causes nominal changes in the properties of the Fe2O3. The observed anomalous mode-softening behavior of the elastic constants is associated with the structural transition at 40-50 GPa, leading to substantial changes in the Debye-like part of the PDOS in the terahertz acoustic phonons. Our experimental and theoretical studies provide new insights into the effects of the structural and electronic transitions in the transition-metal oxide (TMO) compounds. [ABSTRACT FROM AUTHOR]

Abstract  Recent high-pressure studies have shown that an electronic spin transition of iron in ferropericlase, an expected major phase of Earth’s lower mantle, results in changes in its properties, including density, incompressibility, radiative thermal conductivity, electrical conductivity, and sound velocities. To understand the rheology of ferropericlase across the spin transition, we have used in situ radial X-ray diffraction techniques to examine ferropericlase, (Mg0.83,Fe0.17)O, deformed non-hydrostatically in a diamond cell up to 81 GPa at room temperature. Compared with recent quasi-hydrostatic studies, the range of the spin transition is shifted by approximately 20 GPa as a result of the presence of large differential stress in the sample. We also observed a reduction in incompressibility and in the unit cell volume of 3% across the spin transition. Our radial X-ray diffraction results show that the {0 0 1} texture is the dominant lattice preferred orientation in ferropericlase across the spin transition and in the low-spin state. Viscoplastic self-consistent polycrystal plasticity simulations suggest that this preferred orientation pattern is produced by {1 1 0} slip. Analyzing our radial X-ray diffraction patterns using lattice strain theory, we evaluated the lattice d-spacings of ferropericlase and Mo as a function of the ψ angle between the compression direction and the diffracting plane normal. These analyses give the ratio between the uniaxial stress component (t) and the shear modulus (G) under constant stress condition, which represents a proxy for the supported differential stress and elastic strength. This ratio in the mixed-spin and low-spin states is lower than what is expected from previous studies of high-spin ferropericlase, indicating that the spin transition results in a reduced differential stress and elastic strength along with the volume reduction. The influence of the spin transition on the differential stress and strength of ferropericlase is expected to be less dominant across the wide spin transition zone at high pressure–temperature conditions relevant to the lower mantle. [ABSTRACT FROM AUTHOR]

Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; [3]O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earth's lower mantle. [ABSTRACT FROM AUTHOR]

Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extending from about 1000 kilometers in depth and 1900 kelvin to 2200 kilometers and 2300 kelvin in the lower mantle. Because low-spin ferropericlase exhibits higher density and faster sound velocities relative to the high-spin ferropericlase, the observed increase in low-spin (Mg,Fe)O at mid-lower mantle conditions would manifest seismically as a lower-mantle spin transition zone characterized by a steeper-than- normal density gradient. [ABSTRACT FROM AUTHOR]

Synchrotron-based X-ray emission spectroscopy (XES) is well suited to probing the local electronic structure of 3 d transition metals such as Fe and Mn in their host phases. The laser-heated diamond anvil cell technique is uniquely capable of generating ultra-high static pressures and temperatures in excess of 100 GPa and 3000 K. Here X-ray emission spectroscopy and X-ray diffraction have been interfaced with the laser-heated diamond cell for studying the electronic spin states of iron in magnesiowüstite-(Mg0.75,Fe0.25)O and its crystal structure under lower-mantle conditions. X-ray emission spectra of the ferrous iron in a single crystal of magnesiowüstite-(Mg0.75,Fe0.25)O indicate that a high-spin to low-spin transition of ferrous iron occurs at 54 to 67 GPa and 300 K and the ferrous iron remains in the high-spin state up to 47 GPa and 1300 K. This pilot study points to the unique capability of the synchrotron-based XES and X-ray diffraction techniques for addressing the issue of electronic spin transition or crossover in 3 d transition metals and compounds under extreme high- P–T conditions. [ABSTRACT FROM AUTHOR]

This study demonstrates the use of monochromatic synchrotron X-ray radiation of 40 keV for high-precision equation-of-state studies on sets of single crystals analysed individually in the same diamond-anvil pressure cell. Angle-dispersive zone-axis diffraction patterns were obtained from crystals of wustite-Fe0.93O and magnesiowüstite-(Mg0.73Fe0.27)O to 51 GPa in a hydrostatic helium pressure medium. The rhombohedral phase of Fe0.93O was observed above 23 GPa, and its isothermal bulk modulus ( K0) was determined to be 134 (±4) GPa, assuming K′ = 4. The rhombohedral phase of Fe0.93O is more compressible than B1-structured Fe0.93O, with K0 = 146 (±2) GPa. Magnesiowüstite-(Mg0.73Fe0.27)O remains cubic over the experimental pressure range, and has a bulk modulus of 154 (±3) GPa with K′ = 4.0 (±0.1). [ABSTRACT FROM AUTHOR]