Spinel

The Godzilla Megamullion, located in the Parece Vela Backarc Basin of the Izu–Bonin–Mariana (IBM) system, is the largest known example of an Oceanic Core Complex (OCC). Peridotites recovered from the megamullion are divided petrographically into fertile (e.g. lherzolites), depleted (e.g. harzburgites), and plagioclase-bearing groups (Ohara et al., 2003a). A total of 151 thin sections were studied from the Kairei KR03-01, Hakuho Maru KH07-02, and Yokosuka YK09-05 cruises. Melt stagnation is studied via the incidence of plagioclase-bearing peridotites and the major element chemistry of Cr-spinels in the plag-bearing samples. A distinct trend in melt stagnation is evident along the length of the megamullion representing a secular evolution in the entrapment of melts rising through the lithosphere. The distal (furthest from the termination of spreading), depleted portion of the mullion represents a robust mantle section that was still producing abundant melt and can be compared to typical oceanic spreading with its relatively “normal” percentage of plagioclase peridotites and average spinel Cr# of 0.35. The medial, fertile portion of the mullion represents a steep falloff in melt productivity represented by fertile spinel compositions (i.e. Cr# < 0.25) and the presence of plagioclase-free lherzolites. The proximal (closest to termination of spreading), heavily plagioclase impregnated portion (with spinel Cr#s covering nearly the entire range of abyssal peridotite spinel compositions) of the mullion then represents a period of increasing stagnation of melt into a lithosphere that was undergoing progressive thickening. We infer that the processes of mantle evolution through melt stagnation and impregnation, as evidenced by the systematic variations in plag–peridotites along Godzilla Megamullion, represent a possibly common way in which the mantle reacts to OCC formation. In this case, Godzilla Megamullion may represent an extreme endmember in OCC formation.

We report the bulk magnetic properties of a yet unexplored vanadium-based multi-valenced
spinel system, Zn3V3O8. A Curie–Weiss fit of our dc magnetic susceptibility χ(T ) data
in the temperature region of 140–300K yields a Curie constant C = 0.75 cm3Kmole−1 V−1,
θCW = −370 K. We have observed a splitting between the zero field cooled (ZFC) and
field cooled (FC) susceptibility curves below a temperature Tirr of about 6.3K. The value of
the ‘frustration parameter’ ( |θCW|
TN
∼ 100) suggests that the system is strongly frustrated. From
the ac susceptibility measurements we find a logarithmic variation of freezing temperature (Tf )
with frequency ν attesting to the formation of a spin glass below Tf . However, the value of the
characteristic frequency obtained from the Vogel–Fulcher fit suggests that the ground state is
closer to a cluster glass rather than a conventional spin glass. We explored further consequences
of the spin glass behavior and observed aging phenomena and memory effect (both in ZFC and
FC).We found that a positive temperature cycle erases the memory, as predicted by the hierarchical
model. From the heat capacityCP data, a hump-like anomalywas observed inCP /T at about
3.75 K. Below this temperature the magnetic heat capacity shows a nearly linear dependence
with T which is consistent with the formation of a spin glass state below Tf in Zn3V3O8.

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power applications. Furthermore, LMO offers improved thermal stability relative to LiCoO 2 , especially in a highly delithiated state, resulting in safer batteries. [ 6 ] However, a major disadvantage of LMO spinel cathodes is that they lose capacity following long term cycling due to Mn 2+ dissolution from the surface of the cathode into the electrolyte during charge/discharge as a result of the disproportionation reaction: 2Mn 3+ → Mn 4+ + Mn 2+. [ 7,8 ] Approaches that have shown promise in combating manganese dissolution include modifi cation of the composition of the parent LMO electrode by cation substitution (e.g., LiM x Mn 2x O 4 , M = Li, Co, Ni, Zn) [ 9-14 ] to reduce the amount of Mn 3+ in the structure, thereby increasing the average oxidation state on the manganese ions in the electrode above 3.5+. In addition, a variety of protective surface oxide coatings have been employed such as Al 2 O 3 , [ 15 ] ZrO 2 , [ 16 ] Y 2 O 3 , [ 17 ] and TiO 2. [ 7 ] However, the realization of a thin and uniform surface fi lm that does not compromise surface conductivity remains an outstanding challenge. Here, we explore single-layer graphene coatings as an alternative strategy for suppressing manganese dissolution form spinel LMO cathodes. Graphene is a promising candidate for this application since it is an effective diffusion barrier for atomic-scale species [ 18,19 ] and can withstand numerous lithiation charge/discharge cycles. [ 20 ] In addition, graphene is an excellent conductor, which facilitates electron transfer and cycling rate. [ 21 ] Graphene is also known to yield a well-defi ned and stable solid electrolyte interphase (SEI) layer, [ 22 ] which promotes long term lithium-ion battery stability. Consequently, graphene composites and graphitic coatings have been used in lithium-ion battery cathodes with promising results. However, the physical mechanisms that underlie performance improvements, especially relative to the role of graphene in suppressing manganese loss, have not been studied in depth. [ 23-26 ] As shown below, single-layer graphene coatings can significantly reduce the capacity fade of thin-fi lm LMO spinel cathodes in lithium-ion batteries. X-ray photoelectron spectroscopy (XPS) depth profi ling shows that manganese dissolution from graphene-coated LMO cathodes is signifi cantly reduced compared to uncoated LMO cathodes. Furthermore, cross-sectional transmission electron microscopy (TEM) reveals a well-defi ned SEI layer on graphene-coated LMO cathodes. Density functional theory (DFT) calculations provide atomic-scale insight into the mechanisms that underlie the suppression of manganese dissolution by single-layer graphene. Specifi cally, DFT calculations show that common graphene defects are selective diffusion barriers for manganese ions in comparison to lithium. Furthermore, DFT calculations demonstrate that graphene interacts with Mn 3+ ions at the (001) surface of LMO in a manner that increases their oxidation state to Mn 4+ , thus arresting manganese dissolution.

The synthesis of BaTiO3-MgFe2O4 composite powders by a Pechini-like one-pot process and resulting ceramic bodies is described herein. Phase formation during the decomposition of homogenous (Ba,Ti,Fe,Mg)-gels was monitored up to 1200 °C. Composite powders consisting of BaTiO3 and MgFe2O4 were obtained after decomposition at 700 °C for 1 h resulting in crystallite sizes of about 10 nm. The shrinkage and sintering behaviour of compacted powders were examined. Sintering at > 1200 °C leads to the formation of hexagonal BaTiO3 only for composites with a MgFe2O4 content of > 30 wt.%. SEM images of ceramic bodies reveal that the MgFe2O4 particles are surrounded by BaTiO3 crystallites. Magnetic measurements of both powders and corresponding ceramic bodies show ferrimagnetic behaviour with low coercivities. At high-field and low temperatures an additional small paramagnetic contribution was observed which increases with decreasing MgFe2O4 content and should be considered by the calculation of the saturation magnetization.
Finally, the frequency dependent variation of the relative permittivities of the composites was investigated.

Spinels form an interesting class of compounds, finding applications in metal-ion batteries and as catalysts for metal−air batteries and fuel cells. Here, we report a fast, template-free solution combustion method to synthesize nanoscale zinc spinels for applications as cathodes in low-cost aqueous zinc-ion batteries and oxygen reduction reaction (ORR) catalysts. It leads to the formation of phase-pure spinels with near spherical nanoscale morphology. Three spinelsZnCo 2 O 4 (ZCO), ZnMn 2 O 4 (ZMO), and ZnMnCoO 4 (ZMCO)were investigated. ZMO and, for the first time, ZMCO were observed to show reversible Zn (de)insertion involving Mn 4+ /Mn 3+ redox couple with a first discharge capacity of 109.4 mAh/g (i.e., >99% of theoretical capacity). Further, these Zn-based spinels showed appreciable oxygen reduction reaction (ORR) electrocatalytic activity. The ORR activity in alkaline solution was characterized by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) using a rotating disk electrode (RDE) and was observed to be comparable to Pt/C with similar chronoamperometric stability. This enhanced ORR activity can be rooted to the optimal tuning of Co 3+ −O bond strength because of the presence of Mn 3+. This work presents a robust synthesis route to prepare ZnMnCoO 4 spinel acting as an economic cathode material for large-scale Zn-ion batteries for grid storage applications as well as an efficient and stable alternate ORR catalyst in alkaline solution.

The slag's chromium leaching is one of the most pressing concerns in Electric Arc Furnace (EAF) carbon and stainless steels production. In recent years, many studies have aimed at understanding which properties (basicity, cooling speed) and phases (spinels, wustite, silicates) determine the Cr leaching, defining different indices (sp-factor, cs-factor) in order to forecast the slag's behavior compared to the leaching of this toxic metal. The literature suggests that spinel formation is usually a good way to fix Cr and prevent its leaching. However, in some conditions (high basicity, low amount of spinel-forming species) soluble Cr-bearing phases can be formed, i.e., Ca-chromite or unstable spinel. In these conditions, Cr can be leached easily, even if it is bound in a spinel structure. In this paper, the effects of basicity and impurities (Ca, Si) on the instability of Cr-spinel was investigated, with respect to slag mesh. The influence of basicity was also studied on Mg-wustite stability, which might contribute to the leaching of Cr. Different samples of carbon steel slag, suspected of forming unstable spinels, belonging to different steel grade production, were also investigated. Both granulated (4 mm) and milled (< 100 μm) slag were analyzed. Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) analyses were carried out to measure the local chemical composition of Cr-bearing phases. This data was correlated with slag basicity (by X-Ray Fluorescence: XRF), spinel fraction (by X-Ray Diffraction: XRD), and Cr leaching (by Inductively Coupled Plasma Mass Spectrometry: ICP-MS). The main results indicate that the increase of the slag basicity implies an increase of the impurity content (Ca, Si) in the spinel, also over-saturated by Cr. This aspect, coupled with spinel geometrical features, seems to justify the unexpected Cr leaching of some slag samples. Basicity does not influence the chemistry of wustite, thus excluding it as an additional Cr leaching source.

Sol–gel auto-ignition was used to prepare nano-scale magnesium aluminate spinel, using nitrate salts as an oxidizer and glycine–starch mixtures as the fuel. The glycine–starch mixture was varied to understand the effect of fuel mixing ratio on the structural characteristics of the resulting magnesium aluminate.The products were characterized by thermogravimetric-differential thermal analyses, Fourier-transforminfrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area measurements, and trans-mission electron microscopy. The phase purity and crystallite size of the powder products depended on the fuel mixing ratio. The presence of starch in the fuel facilitated the preparation of pure nano-particles.To prepare nano-particles of uniform spherical morphology and diameter of <13 nm, the starch content should be optimized to avoid agglomeration.

A vibronic photoexcitation band at approximately 230 nm was found at 13 K in reactor neutron- and electron-irradiated magnesium aluminate spinel (MgO.nAl2O3). Vibronic structure was found to be temperature dependent and became obscure at over 120 K. Huang Rhys factor S and Debye Temperature D were estimated from the temperature dependence of the 230 nm band by curve-fitting method using Debye approximation. Origin of the vibronic photoexcitation band was suggested as F center.

In the synthesized MgAl 2 O 4 ceramics, Raman scattering modes were detected due to the presence of random distribution of cations over structural positions (structural reversal effects). Irradiation by 10 MeV electron beam caused intensity redistribution of the fundamental bands in Raman spectrum. New optical absorption bands were registered. Observed features were attributed to the effect of radiation-induced 'ionic mixing' in cation sublattice. This effect is the formation of additional [Al] í µí±€í µí±” and [Mg] í µí°´í µí±™ anti-site defects. The obtained data on the defects in transparent ceramics are of interest for the creation of radiation-resistant electromagnetic radiation converters for alternative energy.

Nanostructure-related magnetic properties are investigated systematically for various mesoporous cobalt oxide (Co3O4) and cobalt ferrite (CoFe2O4) spinel phases. Synthesis of the materials by nanocasting offers the opportunity to obtain materials which are different from each other with respect to both specific surface area and crystallite size. As a result, the respective contributions of two types of interfaces, namely, “solid–gas” and “solid–solid” interfaces, to the magnetic ordering can be distinguished. Structural characterization of the porous materials by X-ray diffraction, N2 physisorption, and electron microscopy as well as investigation of the magnetic behavior (field-dependent magnetization and temperature-dependent susceptibility) are presented.