Earth Transition Research Articles

Comparative compressibility of hydrous wadsleyite and ringwoodite: Effect of H2O and implications for detecting water in the transition zone

AbstractReview of recent mineral physics literature shows consistent trends for the influence of Fe and H2O on the bulk modulus (K0) of wadsleyite and ringwoodite, the major phases of Earth's mantle transition zone (410–660 km). However, there is little consensus on the first pressure derivative, K0′ = (dK/dP)P=0, which ranges from about 4 to >5 across experimental studies and compositions. Here we demonstrate the importance of K0′ in evaluating the bulk sound velocity of the transition zone in terms of water content and provide new constraints on the effect of H2O on K0′ for wadsleyite and ringwoodite by conducting a comparative compressibility study. In the experiment, multiple crystals of hydrous Fo90 wadsleyite containing 2.0 and 0.25 wt % H2O were loaded into the same diamond anvil cell, along with hydrous ringwoodite containing 1.4 wt % H2O. By measuring their pressure‐volume evolution simultaneously up to 32 GPa, we constrain the difference in K0′ independent of the pressure scale, finding that H2O has no effect on K0′, whereas the effect of H2O on K0 is significant. The fitted K0′ values of hydrous wadsleyite (0.25 and 2.0 wt % H2O) and hydrous ringwoodite (1.4 wt % H2O) examined in this study were found to be identical within uncertainty, with K0′ ~3.7(2). New secondary‐ion mass spectrometry measurements of the H2O content of these and previously investigated wadsleyite samples shows the bulk modulus of wadsleyite is reduced by 7.0(5) GPa/wt % H2O, independent of Fe content for upper mantle compositions. Because K0′ is unaffected by H2O, the reduction of bulk sound velocity in very hydrous regions of transition zone is expected to be on the order of 1.6%, which is potentially detectible in high‐resolution, regional seismology studies.

Kinetics of the olivine–ringwoodite transformation and seismic attenuation in the Earth's mantle transition zone

In regions of the mantle where multi-phases coexist like at the olivine–wadsleyite–ringwoodite transitions, the stress induced by the seismic waves may drive a mineralogical reaction between the low to high pressure phases, a possible source of dissipation. In such a situation, the amount of attenuation critically depends on the timescale for the phase transformations to reach equilibrium relative to the period of the seismic wave. Here we report synchrotron-based measurements of the kinetics of the olivine to ringwoodite transformation at pressure-temperature conditions of the co-stability loop, for iron-rich olivine compositions. Both microstructural and kinetic data suggest that the transformation rates are controlled by growth processes after the early saturation of nucleation sites along olivine grain boundaries. Transformation-time data show an increase of reaction rates with temperature and iron content, and have been fitted to a rate equation for interface-controlled transformation: G=k0⋅T⋅exp⁡[n⋅XFa]⋅exp⁡[−(ΔHa+PV⁎)/RT]×[1−exp⁡(ΔGr/RT)], where XFa is the fayalite fraction, the exponential factor n=9.7, ln⁡k0=−9.1 ms−1. XFa−1 and ΔHa=199 kJ/mol, assuming V⁎=0 cm3/mol. Including these new kinetic results in a micro-mechanical model of a two-phase loop (Ricard et al., 2009), we predict QK−1 and Qμ−1 significantly higher than the PREM values for both body waves and normal modes. This attests that the olivine–wadsleyite transition can significantly contribute to the attenuation of the Earth's mantle transition zone.

Magnetic Augment in the Nitrogen Substituted Bismuth Ferrite

The nitrogen substituted bismuth ferrite polycrystal sample BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.1</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> has been successfully synthesized using sol-gel method. Its structural and magnetic properties are investigated. The formation of Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> due to charge compensation is found in BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.1</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> from X-ray photoelectron spectra. The crystal structure of BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is barely affected by N doping while the magnetic property is well improved. We propose that it is the coexistence of different superexchanges (Fe-N-Fe and Fe-O-Fe) that breaks the magnetic cancellation effect of the spin spiral, hence increasing the macroscopic magnetization.

Ion size effects on thermoluminescence of terbium and europium doped magnesium orthosilicate

Abstract

Sr, Zn co-doped TiO2 xerogel film made of uniform spheres for high-performance dye-sensitized solar cells

This study comes up with the facile preparation of Sr,Zn co-doped TiO2 xerogel film for boosting the short circuit current density of dye-sensitized solar cells (DSCs). The film contains 2.5-μm-diameter spheres assembled from 60 nm nanoparticles. X-ray photoelectron spectroscopy (XPS) shows that Sr2+ and Zn2+ ions to be well incorporated into the TiO2 crystal lattice without forming specific strontium and zinc compositions. The crystallite size, phase composition, and band structure of the spheres depend on the dopants concentration. Isolated energy levels near valence band as a result of the foreign ions introduction improve the photocatalytic activity of the prepared TiO2 spheres, enhancing the short circuit current density of the cells. The DSC co-doped with 0.075 at.% Sr and 0.4 at.% Zn showed the highest power conversion efficiency of 7.87 % and short circuit current density of 18.75 mA cm−2 thanks to lower charge transfer resistance (2.16 Ω cm2), lower electron transit time (1.19 ms), and higher electron diffusion coefficient (18.1 × 104 cm2 S−1) compared to the other cells, demonstrated by electrochemical impedance spectroscopy (EIS). The concept of the simultaneous introduction of alkaline earth ions and transition ions into TiO2 xerogel films will open up a new insight into the fabrication of high performance DSCs.

High-Entropy Alloys in Hexagonal Close-Packed Structure

The microstructures and properties of high-entropy alloys (HEAs) based on the face-centered cubic and body-centered cubic structures have been studied extensively in the literature, but reports on HEAs in the hexagonal close-packed (HCP) structure are very limited. Using an efficient strategy in combining phase diagram inspection, CALPHAD modeling, and ab initio molecular dynamics simulations, a variety of new compositions are suggested that may hold great potentials in forming single-phase HCP HEAs that comprise rare earth elements and transition metals, respectively. Experimental verification was carried out on CoFeReRu and CoReRuV using X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy.

The Earth transiting the Sun as seen from Jupiter's moons: detection of an inverse Rossiter–McLaughlin effect produced by the opposition surge of the icy Europa

We report on a multi-wavelength observational campaign which followed the Earth's transit on the Sun as seen from Jupiter on 5 Jan the 2014. Simultaneous observations of Jupiter's moons Europa and Ganymede obtained with HARPS from La Silla, Chile, and HARPS-N from La Palma, Canary Islands, were performed to measure the Rossiter-McLaughlin effect due to the Earth's passage using the same technique successfully adopted for the 2012 Venus Transit (Molaro et al 2013). The expected modulation in radial velocities was of about 20 cm/s but an anomalous drift as large as 38 m/s, i.e. more than two orders of magnitude higher and opposite in sign, was detected instead. The consistent behaviour of the two spectrographs rules out instrumental origin of the radial velocity drift and BiSON observations rule out the possible dependence on the Sun's magnetic activity. We suggest that this anomaly is produced by the Opposition Surge on Europa's icy surface, which amplifies the intensity of the solar radiation from a portion of the solar surface centered around the crossing Earth which can then be observed as a a sort of inverse Rossiter-McLaughling effect. in fact, a simplified model of this effect can explain in detail most features of the observed radial velocity anomalies, namely the extensions before and after the transit, the small differences between the two observatories and the presence of a secondary peak closer to Earth passage. This phenomenon, observed here for the first time, should be observed every time similar Earth alignments occur with rocky bodies without atmospheres. We predict it should be observed again during the next conjunction of Earth and Jupiter in 2026.

Enhanced performance of dye-sensitized solar cells aided by Sr,Cr co-doped TiO2 xerogel films made of uniform spheres

One-pot preparation of Sr,Cr co-doped TiO2 xerogel film for boosting the short circuit current density of dye-sensitized solar cells (DSCs) is reported. The 2.5-μm-diameter spheres are assembled from 60nm nanoparticles by a modified sol–gel method. X-ray photoelectron spectroscopy (XPS) shows that Sr2+ and Cr3+ ions to be well incorporated into the titania crystal lattice without forming specific strontium and chromium compositions. The crystallite size, phase composition, and band structure of the particles depend on the dopants concentration. Isolated energy levels near valence band as a result of the transition ion (i.e., Cr) introduction, in conjunction with the local lattice distortions owing to the alkaline earth ion (i.e., Sr) insertion, improves the photocatalytic activity of the prepared TiO2 spheres, enhancing the short circuit current density of the cells. The DSC co-doped with 0.075 at.% Sr and 2.5 at.% Cr (i.e., S7C25 solar cell) showed the highest power conversion efficiency of 7.89% and short circuit current density of 18.58mA/cm2 thanks to lower charge transfer resistance (2.35Ωcm2), lower electron transit time (1.26ms), and higher electron diffusion coefficient (17.1×104cm2S−1) compared to the other cells, demonstrated by electrochemical impedance spectroscopy (EIS). The concept of simultaneously introduction of alkaline earth ions and transition ions into TiO2 lattice will open up a new insight into the fabrication of high performance DSCs.

Vapor–liquid partitioning of alkaline earth and transition metals in NaCl-dominated hydrothermal fluids: An experimental study from 360 to 465 °C, near-critical to halite saturated conditions

Multi-phase fluid flow is a common occurrence in magmatic hydrothermal systems; and extensive modeling efforts using currently established P–V–T–x properties of the NaCl–H2O system are impending. We have therefore performed hydrothermal flow experiments (360–465°C) to observe vapor–liquid partitioning of alkaline earth and first row transition metals in NaCl-dominated source solutions. The data allow extraction of partition coefficients related to the intrinsic changes in both chlorinity and density along the two-phase solvus. The coefficients yield an overall decrease in vapor affinity in the order Cu(I)>Na>Fe(II)>Zn>Ni(II)⩾Mg⩾Mn(II)>Co(II)>Ca>Sr>Ba, distinguished with 95% confidence for vapor densities greater than ∼0.2g/cm3. The alkaline earth metals are limited to purely electrostatic interactions with Cl ligands, resulting in an excellent linear correlation (R2>0.99) between their partition coefficients and respective ionic radii. Though broadly consistent with this relationship, relative behavior of the transition metals is not well resolved, being likely obscured by complex bonding processes and the potential participation of Na in the formation of tetra-chloro species. At lower densities (at/near halite saturation) partitioning behavior of all metals becomes highly non-linear, where M/Cl ratios in the vapor begin to increase despite continued decreases in chlorinity and density. We refer to this phenomenon as “volatility”, which is broadly associated with substantial increases in the HCl/NaCl ratio (eventually to >1) due to hydrolysis of NaCl. Some transition metals (e.g., Fe, Zn) exhibit volatility prior to halite stability, suggesting a potential shift in vapor speciation relative to nearer critical regions of the vapor–liquid solvus. The chemistry of deep-sea hydrothermal fluids appears affected by this process during magmatic events, however, our results do not support suggestions of subseafloor halite precipitation recorded in currently available field data. Ca–Cl systematics in vent fluids are specifically explored, revealing behavior consistent with partitioning due to phase separation. Interestingly, the effect of variable chloride on dissolved Na/Ca ratios associated with plagioclase solubility (in single-phase solutions) appears fundamentally similar to that of phase separation on vapor compositions such that vapors evolved in hydrothermal systems may naturally remain near equilibrium with the host lithology. Conversely, residual liquids/brines left behind in the crust may be undersaturated with metals, enhancing the rate and extent of hydrothermal alteration.

Continental flood basalts derived from the hydrous mantle transition zone.

It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can potentially account for the chemical diversity of many continental flood basalts.

Transition Probabilities and Oscillator Strengths for E1 Transitions of Ce III

The lanthanide elements (Z = 57−71) are important in astrophysics in relation to nucleosynthesis and star formation considerations. Spectroscopic investigations of the doubly ionized elements of this group are motivated by astrophysical interest because, in the hot chemically peculiar (CP) stars, there is an overwhelming presence of lines belonging to the third spectrum which corresponds to the dominant ionization stage [1]. The rare-earth element cerium has a particularly rich, even by rare-earth standards, optical emission spectrum from both its neutral and singly ionized stages. This characteristic has made cerium attractive for use in highintensity discharge light sources where it improves both luminous e cacy and colour rendering [2]. The works for energy levels and lifetimes of doubly ionized cerium (Ce III) can be found in, for example, [3 7]. Many strong lines of cerium in the ultraviolet evidently arise from doubly ionized atoms. King and King published a list of these [8]. Triplet and singlet terms of Ce III were reported by Russell et al. [9]. Observations of the third spectrum of cerium from 757 to 11091 A were given by Sugar [10]. The 4f 4f5d lines of Ce III were measured by Johansson and Litzen [11]. Bord and co-workers calculated oscillator strengths for some Ce III lines [12]. Later, the spectroscopic analysis of Ce III was extended. Wyart and Palmeri gave a list of computed oscillator strengths for some selected transitions [6]. Transition probabilities for Ce III were obtained from branching fractions calculated by Cowan code and experimental lifetimes by Li and co-workers [7]. Biemont et al. emphasized the importance of corepolarization e ects on oscillator strength determination in Ce III [1]. The multicon guration Dirac Fock calculation of the transition energies and oscillator strengths for the 6s S0 6s6p P1, P1 transitions in rare earth

Rheology of Mg2GeO4 olivine and spinel harzburgite: Implications for Earth's mantle transition zone

AbstractGeophysical modeling requires an upper mantle low‐viscosity zone (LVZ); recent results suggest that the LVZ could be within the mantle transition zone (MTZ) or above it, depending on boundary conditions. The rheology of the olivine‐dominated uppermost mantle is well constrained experimentally but not the MTZ. Here we report first‐time measurement of the rheology of Mg2GeO4 spinel (analogue of ringwoodite, the dominant mineral of the lower MTZ) in the dislocation creep regime and compare it with that of Mg2GeO4 olivine. In both cases, we incorporate 15–20% pyroxene, the second most abundant mineral in the upper mantle to provide a realistic comparison of rock rheologies. Under similar conditions, spinel‐dominated material is about twice as strong as olivine‐dominated material. Our results suggest that unless H2O weakening of ringwoodite or phase‐transformation‐induced grain size reduction occurs in the lower MTZ, it will be more viscous than above the 410 km discontinuity.

Silicon/Hollow γ-Fe2O3 Nanoparticles as Efficient Anodes for Li-Ion Batteries

Nanomaterials have triggered a lot of attention as potential triggers for a technological breakthrough in Energy Storage Devices and specifically Li-ion batteries. Herein, we report the original synthesis of well-defined silicon/iron oxide nanoparticles and its application as anode materials for Li-ion batteries. This model compound is based on earth abundant elements and allows for a full investigation of the electrochemical reactions through its iron oxide magnetic phase. The elaboration of silicon with iron oxide grown on its surface has been achieved by reacting an organometallic precursor Fe(CO)5 with Si nanopowder and subsequent slow oxidation step in air yields hollow γ-Fe2O3 on the Si surface. This specific morphology results in an enhancement of the specific capacity from 2000 mAh/gSi up to 2600 mAh/gSi. Such a high specific capacity is achieved only for hollow γ-Fe2O3 and demonstrates a novel approach toward the modification of electrode materials with an earth abundant transition metal like iron. This result further emphasizes the need for precisely designed nanoparticles in achieving significant progress in energy storage.

Light emission from rare-earths in dislocation engineered silicon substrates

We report and compare the luminescence, both photo- and electroluminescence, in the near-infrared of a wide range of rare earths (Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) doped dislocation engineered silicon light emitting devices. The rare earths are introduced using ion implantation into standard Czochralski (CZ) n-type silicon wafers pre-implanted with boron to form both the p–n junction and an engineered dislocation loop array. Rare earth internal transitions are observed in samples co-doped with Dy, Ho, Er, and Tm. We show that for each rare earth optimizing the optical activity depends critically on the rare earth implant parameters and post-implant process conditions. Room temperature operation in the 1.5 and 2.0 µm spectral regions is observed from the internal rare earth transitions in Er and Tm.

Targeted crystal growth of rare Earth intermetallics with synergistic magnetic and electrical properties: structural complexity to simplicity.

The single-crystal growth of extended solids is an active area of solid-state chemistry driven by the discovery of new physical phenomena. Although many solid-state compounds have been discovered over the last several decades, single-crystal growth of these materials in particular enables the determination of physical properties with respect to crystallographic orientation and the determination of properties without possible secondary inclusions. The synthesis and discovery of new classes of materials is necessary to drive the science forward, in particular materials properties such as superconductivity, magnetism, thermoelectrics, and magnetocalorics. Our research is focused on structural characterization and determination of physical properties of intermetallics, culminating in an understanding of the structure-property relationships of single-crystalline phases. We have prepared and studied compounds with layered motifs, three-dimensional magnetic compounds exhibiting anisotropic magnetic and transport behavior, and complex crystal structures leading to intrinsically low lattice thermal conductivity. In this Account, we present the structural characteristics and properties that are important for understanding the magnetic properties of rare earth transition metal intermetallics grown with group 13 and 14 metals. We present phases adopting the HoCoGa5 structure type and the homologous series. We also discuss the insertion of transition metals into the cuboctahedra of the AuCu3 structure type, leading to the synthetic strategy of selecting binaries to relate to ternary intermetallics adopting the Y4PdGa12 structure type. We provide examples of compounds adopting the ThMn12, NaZn13, SmZn11, CeCr2Al20, Ho6Mo4Al43, CeRu2Al10, and CeRu4Al16-x structure types grown with main-group-rich self-flux methods. We also discuss the phase stability of three related crystal structures containing atoms in similar chemical environments: ThMn12, CaCr2Al10, and YbFe2Al10. In addition to dimensionality and chemical environment, complexity is also important in materials design. From relatively common and well-studied intermetallic structure types, we present our motivation to work with complex stannides adopting the Dy117Co57Sn112 structure type for thermoelectric applications and describe a strategy for the design of new magnetic intermetallics with low lattice thermal conductivity. Our quest to grow single crystals of rare-earth-rich complex stannides possessing low lattice thermal conductivity led us to discover the new structure type Ln30Ru4+xSn31-y (Ln = Gd, Dy), thus allowing the correlation of primitive volumes with lattice thermal conductivities. We highlight the observation that Ln30Ru4+xSn31-y gives rise to highly anisotropic magnetic and transport behavior, which is unexpected, illustrating the need to measure properties on single crystals.

Silver nitroprusside: Atypical coordination within the metal nitroprussides series

The nitroprusside complex anion forms an insoluble salt, of formula unit Ag2[Fe(CN)5NO], when it reacts with an aqueous solution of Ag+. Related to the high insolubility of silver halides, silver nitroprusside is a good intermediate to obtain soluble nitroprussides of alkaline, alkaline earth and trivalent transition metals. No other applications for that solid have been reported, probably because its crystal structure and related properties are unknown. This contribution reports the crystal structure for the titled compound from X-ray powder diffraction data and its refinement using the Rietveld method. It crystallizes with a monoclinic unit cell, in the Pc space group, with cell parameters: a=7.4254(3), b=6.4121(2), c=11.8729(2)Å, β=115.16(1)°. The crystal structure has two sites for the silver atom, corresponding to its coordination two and three to the N ends of CN groups. Calculation of the radial distribution function and IR and UV–Vis spectra provided the a priori structural information required to support the selected structural model to be refined. Such information was then used to validate the refined structure. The structure of this compound is atypical within the metal nitroprussides series. The thermal decomposition in air and nitrogen atmosphere of the title compound was studied from thermogravimetry and IR combined techniques. In the solid residues metallic silver and iron oxide (hematite) were identified.

Design and construction of new potentiometric sensors for determination of Al3+ ion based on (Z)-2-(2-methyl benzylidene)-1-(2,4-dinitrophenyl) hydrazine.

(Z)-2-(2-methyl benzylidene)-1-(2,4-dinitrophenyl) hydrazine (L) was used as an active component of PVC membrane electrode (PME), coated graphite electrode (CGE) and coated silver wire electrode (CWE) for sensing Al(3+) ion. The electrodes exhibited linear Nernstian responses to Al(3+) ion in the concentration range of 1.0×10(-6) to 1.0×10(-1)M (for PME, LOD=8.8×10(-7)M), 5.5×10(-7) to 2.0×10(-1)M (for CWE, LOD=3.3×10(-7)M) and 1.5×10(-7) to 1.0×10(-1)M (for CGE, LOD=9.2×10(-8)M). The best performances were observed with the membranes having the composition of L:PVC:NPOE:NaTPB in the ratio of 5:35:57:3 (w/w; mg). The electrodes have a response time of 6s and an applicable pH range of 3.5-9.1. The sensors have a lifetime of about 15weeks and exhibited excellent selectivity over a number of mono-, bi-, and tri-valent cations including alkali, alkaline earth metal, heavy and transition metal ions. Analytical utility of the proposed sensor has been further tested by using it as an indicator electrode in the potentiometric titration of Al(3+) with EDTA. The electrode was also successfully applied for the determination of Al(3+) ion in real and pharmaceutical samples.

Фазовые равновесия и термодинамические свойства оксидов в системах на основе редкоземельных, щелочноземельных и 3d-переходных (Mn, Fe, Co) металлов. Краткий обзор

Review is dedicated studies of phase equilibria in the systems based on rare earth elements and 3d transition metals. It’s highlighted several structural families of these compounds and is shown that many were found interesting properties for practical application, such as high conductivity up to the superconducting state, magnetic properties, catalytic activity of the processes of afterburning of exhaust gases, the high mobility in the oxygen sublattice and more.

Rare earth–metal bonding in molecular compounds: recent advances, challenges, and perspectives

In this review, all structurally authenticated molecular compounds with direct bonds between rare earth metals and transition or main group metals are summarized. Novel aspects of their syntheses, properties and reactivities are highlighted.

57 Fe Mössbauer and magnetic studies of Nd3Fe24.5Cr4.5

The structural and magnetic properties of the rare earth transition metal compound Nd 3Fe 24.5Cr 4.5 have been investigated by variable temperature high resolution x-ray diffraction together with DC magnetization and 57Fe Mossbauer effect measurements. The magnetic ordering temperature has been found to be T C= 423(5) K with spin reorientation detected below room temperature around T sr= 158(5) K. Rietveld refinements indicate that Nd 3Fe 24.5Cr 4.5 crystallizes in the Nd 3(Fe,Ti) 29-type structure with the A2/m space group and a substantial magneto-volume effect is detected around T C. The Mossbauer spectra can be fitted well using five sub-spectra. The temperature dependence of the average hyperfine field has been analysed in terms of different power laws of the reduced temperature. The Debye temperature of Nd 3Fe 24.5Cr 4.5 has been determined as 𝜃D= 400(± 30) K from a fit to the variable temperature isomer shift IS(T).