Measuring the Electrical Resistivity of Liquid Iron to 1.4 Mbar.

We determined the electrical resistivity of liquid Fe to 135 GPa and 6680 K using a four-probe method in a diamond-anvil cell combined with two novel techniques: (i) enclosing a molten Fe in a sapphire capsule, and (ii) millisecond time-resolved simultaneous measurements of the resistance, x-ray diffraction, and temperature of instantaneously melted Fe. Our results show the minimal temperature dependence of the resistivity of liquid Fe and its anomalous resistivity decrease around 50 GPa, likely associated with a gradual magnetic transition, both in agreement with previous ab initio calculations.

X-ray focusing to 62 keV by compound refractive lenses for high-pressure x-ray diffraction.

This study describes high-energy x-ray focusing optics using compound refractive lenses (CRLs) for high-pressure x-ray diffraction (XRD) with a monochromatic x-ray beam. A CRL-based x-ray transfocator was upgraded and installed in the optics hutch at the BL10XU beamline of SPring-8. The instrument can be equipped with two types of CRLs in parallel: a newly designed aluminum (Al) CRL for x-ray energies of 40-62 keV and an existing glassy carbon CRL for those up to 40 keV. In only the Al-CRL-based x-ray transfocator, a 62 keV monochromatic x-ray beam with horizontal (H) and vertical (V) focused spots, whose sizes were 189 and 10.5 µm, respectively, and a flux of 1.32 × 1011 phs/s were generated. A polymer SU-8 CRL fabricated via deep x-ray lithography was installed to further reduce the x-ray beam size. The Al-CRL and the SU-8 CRL were combined to generate a smaller spot size of 12.5 (H) × 11.0 (V) µm2 with a flux of 3 × 1010 phs/s at 62 keV. A two-step optical configuration combining an x-ray transfocator and SU-8 CRL provides a valuable method for high-pressure XRD using a high-energy x-ray focused beam. The optical design and performance of the Al-CRL-based x-ray transfocator, its combination with the SU-8 CRL, and the first results of the focusing optics commissioning are presented here.

High-pressure melting experiments of Fe3S and a thermodynamic model of the Fe-S liquids for the Earth's core.

Melting experiments on Fe3S were conducted to 75 GPa and 2800 K in laser-heated and internally resistive-heated diamond anvil cells within-situx-ray diffraction and/or post-mortem textural observation. From the constrained melting curve, we assessed the thermal equation of state for Fe3S liquid. Then we constructed a thermodynamic model of melting of the system Fe-Fe3S including the eutectic relation under high pressures based on our new experimental data. The mixing properties of Fe-S liquids under high pressures were evaluated in order to account for existing experimental data on eutectic temperature. The results demonstrate that the mixing of Fe and S liquids are nonideal at any core pressure. The calculated sulphur content in eutectic point decreases with increasing pressure to 120 GPa and is fairly constant of 8 wt% at greater pressures. From the Gibbs free energy, we derived the parameters to calculate the crystallising point of an Fe-S core and its isentrope, and then we calculated the density and the longitudinal seismic wave velocity (Vp) of these liquids along each isentrope. While Fe3S liquid can account for the seismologically constrained density andVpprofiles over the outer core, the density of the precipitating phase is too low for the inner core. On the other hand, a hypothetical Fe-S liquid core with a bulk composition on the Fe-rich side of the eutectic point cannot represent the density andVpprofiles of the Earth's outer core. Therefore, Earth's core cannot be approximated by the system Fe-S and it should include another light element.

Melting phase relations in Fe-Si-H at high pressure and implications for Earth's inner core crystallization.

Hydrogen could be an important light element in planetary cores, but its effect on phase diagrams of iron alloys is not well known because the solubility of H in Fe is minimal at ambient pressure and high-pressure experiments on H-bearing systems have been challenging. Considering that silicon can be another major light element in planetary cores, here we performed melting experiments on the Fe-Si-H system at ~ 50 GPa and obtained the ternary liquidus phase relations and the solid/liquid partition coefficient, D of Si and H based on in-situ high-pressure X-ray diffraction measurements and ex-situ chemical and textural characterizations on recovered samples. Liquid crystallized hexagonal close-packed (hcp) (Fe0.93Si0.07)H0.25, which explains the observed density and velocities of the Earth's solid inner core. The relatively high DSi = 0.94(4) and DH = 0.70(12) suggest that in addition to Si and H, the liquid outer core includes other light elements such as O, which is least partitioned into solid Fe and can thus explain the density difference between the outer and inner core. H and O, as well as Si, are likely to be major core light elements, supporting the sequestration of a large amount of water in the Earth's core.

Stratification in planetary cores by liquid immiscibility in Fe-S-H.

Liquid-liquid immiscibility has been widely observed in iron alloy systems at ambient pressure and is important for the structure and dynamics in iron cores of rocky planets. While such previously known liquid immiscibility has been demonstrated to disappear at relatively low pressures, here we report immiscible S(±Si,O)-rich liquid and H(±C)-rich liquid above ~20 GPa, corresponding to conditions of the Martian core. Mars' cosmochemically estimated core composition is likely in the miscibility gap, and the separation of two immiscible liquids could have driven core convection and stable stratification, which explains the formation and termination of the Martian planetary magnetic field. In addition, we observed liquid immiscibility in Fe-S-H(±Si,O,C) at least to 118 GPa, suggesting that it can occur in the Earth's topmost outer core and form a low-velocity layer below the core-mantle boundary.

Low-spin ferric iron in primordial bridgmanite crystallized from a deep magma ocean.

The crystallization of the magma ocean resulted in the present layered structure of the Earth's mantle. An open question is the electronic spin state of iron in bridgmanite (the most abundant mineral on Earth) crystallized from a deep magma ocean, which has been neglected in the crystallization history of the entire magma ocean. Here, we performed energy-domain synchrotron Mössbauer spectroscopy measurements on two bridgmanite samples synthesized at different pressures using the same starting material (Mg0.78Fe0.13Al0.11Si0.94O3). The obtained Mössbauer spectra showed no evidence of low-spin ferric iron (Fe3+) from the bridgmanite sample synthesized at relatively low pressure of 25 gigapascals, while that directly synthesized at a higher pressure of 80 gigapascals contained a relatively large amount. This difference ought to derive from the large kinetic barrier of Fe3+ rearranging from pseudo-dodecahedral to octahedral sites with the high-spin to low-spin transition in experiments. Our results indicate a certain amount of low-spin Fe3+ in the lower mantle bridgmanite crystallized from an ancient magma ocean. We therefore conclude that primordial bridgmanite with low-spin Fe3+ dominated the deeper part of an ancient lower mantle, which would contribute to lower mantle heterogeneity preservation and call for modification of the terrestrial mantle thermal evolution scenarios.

Experimental evidence for hydrogen incorporation into Earth's core.

Hydrogen is one of the possible alloying elements in the Earth's core, but its siderophile (iron-loving) nature is debated. Here we experimentally examined the partitioning of hydrogen between molten iron and silicate melt at 30-60 gigapascals and 3100-4600 kelvin. We find that hydrogen has a metal/silicate partition coefficient DH ≥ 29 and is therefore strongly siderophile at conditions of core formation. Unless water was delivered only in the final stage of accretion, core formation scenarios suggest that 0.3-0.6 wt% H was incorporated into the core, leaving a relatively small residual H2O concentration in silicates. This amount of H explains 30-60% of the density deficit and sound velocity excess of the outer core relative to pure iron. Our results also suggest that hydrogen may be an important constituent in the metallic cores of any terrestrial planet or moon having a mass in excess of ~10% of the Earth.

Equation of State of Liquid Iron under Extreme Conditions.

The density of liquid iron has been determined up to 116 GPa and 4350 K via static compression experiments following an innovative analysis of diffuse scattering from liquid. The longitudinal sound velocity was also obtained to 45 GPa and 2700 K based on inelastic x-ray scattering measurements. Combining these results with previous shock-wave data, we determine a thermal equation of state for liquid iron. It indicates that Earth's outer core exhibits 7.5%-7.6% density deficit, 3.7%-4.4% velocity excess, and an almost identical adiabatic bulk modulus, with respect to liquid iron.

Pressure-Induced Charge Disorder-Order Transition in the Cs4O6 Sesquioxide.

Cs4O6 adopts two distinct crystal structures at ambient pressure. At temperatures below ∼200 K, its ground state structure is tetragonal, incorporating two symmetry-distinct dioxygen anions, diamagnetic peroxide, O22-, and paramagnetic superoxide, O2-, units in a 1:2 ratio, consistent with the presence of charge and orbital order. At high temperatures, its ground state structure is cubic, comprising symmetry-equivalent dioxygen units with an average oxidation state of -4/3, consistent with the adoption of a charge-disordered state. The pressure dependence of the structure of solid Cs4O6 at 300 K and at 13.4 K was followed up to ∼12 GPa by synchrotron X-ray powder diffraction. When a pressure of ∼2 GPa is reached at ambient temperature, an incomplete phase transition that is accompanied by a significant volume reduction (∼2%) to a more densely packed highly anisotropic tetragonal structure, isostructural with the low-temperature ambient-pressure phase of Cs4O6, is encountered. A complete transformation of the cubic (charge-disordered) to the tetragonal (charge-ordered) phase of Cs4O6 is achieved when the hydrostatic pressure exceeds 6 GPa. In contrast, the pressure response of the Cs4O6 cubic/tetragonal phase assemblage at 13.4 K is distinctly different with the cubic and tetragonal phases coexisting over the entire pressure range (to ∼12 GPa) accessed in the present experiments and with only a small fraction of the cubic phase converting to tetragonal. Pressure turns out to be an inefficient stimulus to drive the charge disorder-order transition in Cs4O6 at cryogenic temperatures, presumably due to the high activation barriers (much larger than the thermal energy at 13.4 K) associated with the severe steric hindrance for a rotation of the molecular oxygen units necessitated in the course of the structural transformation.

At-wavelength optics characterisation via X-ray speckle- and grating-based unified modulated pattern analysis.

The current advances in new generation X-ray sources are calling for the development and improvement of high-performance optics. Techniques for high-sensitivity phase sensing and wavefront characterisation, preferably performed at-wavelength, are increasingly required for quality control, optimisation and development of such devices. We here show that the recently proposed unified modulated pattern analysis (UMPA) can be used for these purposes. We characterised two polymer X-ray refractive lenses and quantified the effect of beam damage and shape errors on their refractive properties. Measurements were performed with two different setups for UMPA and validated with conventional X-ray grating interferometry. Due to its adaptability to different setups, the ease of implementation and cost-effectiveness, we expect UMPA to find applications for high-throughput quantitative optics characterisation and wavefront sensing.

Emergence of a new valence-ordered structure and collapse of the magnetic order under high pressure in EuPtP.

The layered hexagonal EuPtP is a rare substance that exhibits two successive valence transitions occurring simultaneously with valence ordering transitions and an antiferromagnetic order. Anticipating that the application of pressure to this sample would induce a new valence-ordered structure and/or a new phenomenon associated with valence fluctuation, we examined the electrical resistivity ρ, the Eu L3-edge x-ray absorption spectroscopy, and the powder x-ray diffraction under high pressure. We found a new valence transition at around P = 2.5 GPa. After the transition, a new valence-ordered structure is realized at the lowest temperature. The valence-ordered structure is inferred to be stacking of [Formula: see text] (2+: Eu2+ layer, 3+: Eu3+ layer) along the c-axis. Upon further increases in pressure, the valence-ordered structure is suppressed and another valance-ordered phase is realized up to P = 6 GPa. The antiferromagnetic order collapses in the pressure range between 6 GPa and 8 GPa.

Prognostic Impact of Serum Albumin Concentration for Neurologically Favorable Outcome in Patients Treated with Targeted Temperature Management After Out-of-Hospital Cardiac Arrest: A Multicenter Prospective Study.

To assess whether serum albumin concentration measured upon hospital arrival was useful as an early prognostic biomarker for neurologically favorable outcome in out-of-hospital cardiac arrest (OHCA) patients treated with target temperature management (TTM). This prospective, multicenter observational study (The CRITICAL Study) carried out between July 1, 2012 and December 31, 2014 in Osaka Prefecture, Japan involving 13 critical care medical centers (CCMCs) and one non-CCMC with an emergency department. This study included patients ≥18 years of age who underwent an OHCA, for whom resuscitation was attempted by Emergency Medical Services personnel and were then transported to participating institutions, and who were then treated with TTM. Based on the serum albumin concentration upon hospital arrival, involved patients were divided into four quartiles (Q1-Q4) defined as Q1 (<3.0 g/dL), Q2 (≥3.0, <3.4 g/dL), Q3 (≥3.4, <3.8 g/dL), and Q4 (≥3.8 g/dL). The primary outcome of this study was 1-month survival with neurologically favorable outcome defined by cerebral performance category 1 or 2. During the study period, a total of 327 were eligible for our analysis. The overall proportion of neurologically favorable outcome was 33.0% (108/327). The Q4 group had the highest proportion of neurologically favorable outcome (52.5% [48/91]), followed by Q3 (34.5% [30/87]), Q2 (27.3% [21/77]), and Q1 (12.5% [9/72]). The multivariable logistic regression analysis demonstrated that the proportion of neurologically favorable outcome was significantly higher in the Q4 group than that in the Q1 group (adjusted odds ratio 10.39; 95% confidence interval 3.36-32.17). The adjusted proportion of neurologically favorable outcome increased in a stepwise fashion across increasing quartiles (p < 0.001). In this study, higher serum albumin concentration upon hospital arrival had a positive association with neurologically favorable outcome after OHCA in a dose-dependent manner.

Effect of Serum Albumin Concentration on Neurological Outcome After Out-of-Hospital Cardiac Arrest (from the CRITICAL [Comprehensive Registry of Intensive Cares for OHCA Survival] Study in Osaka, Japan).

The aim of this study was to assess whether serum albumin concentration upon hospital arrival had prognostic indications on out-of-hospital cardiac arrest (OHCA). This prospective, multicenter observational study conducted in Osaka, Japan (the CRITICAL [Comprehensive Registry of Intensive Cares for OHCA Survival] study), enrolled all patients with consecutive OHCA transported to 14 participating institutions. We included adult patients aged ≥18 years with nontraumatic OHCA who achieved return of spontaneous circulation and whose serum albumin concentration was available from July 2012 to December 2014. Based on the serum albumin concentration upon hospital arrival, patients were divided into quartiles (Q1 to Q4), namely, Q1 (<2.7 g/dl), Q2 (2.7 to 3.1 g/dl), Q3 (3.1 to 3.6 g/dl), and Q4 (≥3.6 g/dl). The primary outcome was 1-month survival with favorable neurological outcome (cerebral performance category scale 1 or 2). During the study period, a total of 1,269 patients with OHCA were eligible for our analyses. The highest proportion of favorable neurological outcome was 33.5% (109 of 325) in the Q4 group, followed by 13.2% (48 of 365), 5.0% (13 of 261), and 3.5% (11 of 318) in the Q3, Q2, and Q1 groups, respectively. In the multivariable logistic regression analysis, the proportion of favorable neurological outcome in the Q4 group was significantly higher, compared with that in the Q1 group (adjusted odds ratio 8.61; 95% confidence interval 4.28 to 17.33). The adjusted proportion of favorable neurological outcome increased in a stepwise manner across increasing quartiles (p for trend <0.001). Higher serum albumin concentration was significantly and independently associated with favorable neurological outcome in a dose-dependent manner.

An Exceptionally Narrow Band-Gap (∼4 eV) Silicate Predicted in the Cubic Perovskite Structure: BaSiO3.

The electronic structures of 35 A2+B4+O3 ternary cubic perovskite oxides, including their hypothetical chemical compositions, were calculated by a hybrid functional method with the expectation that peculiar electronic structures and unique carrier transport properties suitable for semiconductor applications would be hidden in high-symmetry cubic perovskite oxides. We found unique electronic structures of Si-based oxides (A = Mg, Ca, Sr, and Ba, and B = Si). In particular, the unreported cubic BaSiO3 has a very narrow band gap (4.1 eV) compared with conventional nontransition-metal silicates (e.g., ∼9 eV for SiO2 and the calculated value of 7.3 eV for orthorhombic BaSiO3) and a small electron effective mass (0.3m0, where m0 is the free electron rest mass). The narrow band gap is ascribed to the nonbonding state of Si 3s and the weakened Madelung potential. The existence of the predicted cubic perovskite structure of BaSiO3 was experimentally verified by applying a high pressure of 141 GPa. The present finding indicates that it could be possible to develop a new transparent oxide semiconductor of earth abundant silicates if the symmetry of its crystal structure is appropriately chosen. Cubic BaSiO3 is a candidate for high-performance oxide semiconductors if this phase can be stabilized at room temperature and ambient pressure.

Pressure dependence of transverse acoustic phonon energy in ferropericlase across the spin transition.

We investigated transverse acoustic (TA) phonons in iron-bearing magnesium oxide (ferropericlase) up to 56 GPa using inelastic x-ray scattering (IXS). The results show that the energy of the TA phonon far from the Brillouin zone center suddenly increases with increasing pressure above the spin transition pressure of ferropericlase. Ab initio calculations revealed that the TA phonon energy far from the Brillouin zone center is higher in the low-spin state than in the high spin state; that the TA phonon energy depend weakly on pressure; and that the energy gap between the TA and the lowest-energy-optic phonons is much narrower in the low-spin state than in the high-spin state. This allows us to conclude that the anomalous behavior of the TA mode in the present experiments is the result of gap narrowing due to the spin transition and explains contradictory results in previous experimental studies.

Diamond formation in the deep lower mantle: a high-pressure reaction of MgCO3 and SiO2.

Diamond is an evidence for carbon existing in the deep Earth. Some diamonds are considered to have originated at various depth ranges from the mantle transition zone to the lower mantle. These diamonds are expected to carry significant information about the deep Earth. Here, we determined the phase relations in the MgCO3-SiO2 system up to 152 GPa and 3,100 K using a double sided laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction. MgCO3 transforms from magnesite to the high-pressure polymorph of MgCO3, phase II, above 80 GPa. A reaction between MgCO3 phase II and SiO2 (CaCl2-type SiO2 or seifertite) to form diamond and MgSiO3 (bridgmanite or post-perovsktite) was identified in the deep lower mantle conditions. These observations suggested that the reaction of the MgCO3 phase II with SiO2 causes formation of super-deep diamond in cold slabs descending into the deep lower mantle.

The Room-Temperature Superionic Conductivity of Silver Iodide Nanoparticles under Pressure.

We performed variable-temperature synchrotron powder X-ray diffraction measurements and impedance spectroscopy under pressure for silver iodide (AgI) nanoparticles with a diameter of 11 nm. The superionic conducting α-phase of AgI nanoparticles was successfully stabilized down to at least 20 °C by applying a pressure of 0.18 GPa, whereas the transition temperature was 147 °C in bulk AgI at ambient pressure. To our knowledge, this is the first example of the α-phase of AgI existing stably at room temperature.

Pressure-induced Transformations of Dense Carbonyl Sulfide to Singly Bonded Amorphous Metallic Solid.

The application of pressure, internal or external, transforms molecular solids into non-molecular extended network solids with diverse crystal structures and electronic properties. These transformations can be understood in terms of pressure-induced electron delocalization; however, the governing mechanisms are complex because of strong lattice strains, phase metastability and path dependent phase behaviors. Here, we present the pressure-induced transformations of linear OCS (R3m, Phase I) to bent OCS (Cm, Phase II) at 9 GPa; an amorphous, one-dimensional (1D) polymer at 20 GPa (Phase III); and an extended 3D network above ~35 GPa (Phase IV) that metallizes at ~105 GPa. These results underscore the significance of long-range dipole interactions in dense OCS, leading to an extended molecular alloy that can be considered a chemical intermediate of its two end members, CO2 and CS2.

Emergence of superconductivity in (NH3)yMxMoSe2 (M: Li, Na and K).

We report syntheses of new superconducting metal-doped MoSe2 materials (MxMoSe2). The superconducting MxMoSe2 samples were prepared using a liquid NH3 technique, and can be represented as '(NH3)yMxMoSe2'. The Tcs of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH3)yNaxMoSe2 were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe2 layers. The x-independence of c was observed in (NH3)yNaxMoSe2, indicating the formation of a stoichiometric compound in the entire x range, which is consistent with the x-independence of Tc. A metallic edge of the Fermi level was observed in the photoemission spectrum at 30 K, demonstrating its metallic character in the normal state. Doping of MoSe2 with Li and K also yielded superconductivity. Thus, MoSe2 is a promising material for designing new superconductors, as are other transition metal dichalcogenides.

Experimental determination of the electrical resistivity of iron at Earth's core conditions.

Earth continuously generates a dipole magnetic field in its convecting liquid outer core by a self-sustained dynamo action. Metallic iron is a dominant component of the outer core, so its electrical and thermal conductivity controls the dynamics and thermal evolution of Earth's core. However, in spite of extensive research, the transport properties of iron under core conditions are still controversial. Since free electrons are a primary carrier of both electric current and heat, the electron scattering mechanism in iron under high pressure and temperature holds the key to understanding the transport properties of planetary cores. Here we measure the electrical resistivity (the reciprocal of electrical conductivity) of iron at the high temperatures (up to 4,500 kelvin) and pressures (megabars) of Earth's core in a laser-heated diamond-anvil cell. The value measured for the resistivity of iron is even lower than the value extrapolated from high-pressure, low-temperature data using the Bloch-Grüneisen law, which considers only the electron-phonon scattering. This shows that the iron resistivity is strongly suppressed by the resistivity saturation effect at high temperatures. The low electrical resistivity of iron indicates the high thermal conductivity of Earth's core, suggesting rapid core cooling and a young inner core less than 0.7 billion years old. Therefore, an abrupt increase in palaeomagnetic field intensity around 1.3 billion years ago may not be related to the birth of the inner core.