Cation Diffusion Research Articles

Structural and chemical evolutions of a magnesium vanadium oxide cathode under electrochemical cycling in magnesium batteries

The design of cathode materials that remain chemically and structurally stable during repetitive ion insertion and extraction poses a significant challenge in developing multivalent batteries. The cycling stability of traditional metal oxide-based cathode is challenged by sluggish diffusion of multivalent cations and parasitic reactivity at interfacial regimes, including the cathode electrolyte interphase layer (CEI). Understanding the reactions at the cathode-electrolyte interface, particularly those induced by non-stoichiometric surface layers, is a crucial design parameter for both cathode materials and electrolytes. In this study, we employed multimodal analysis, including in situ and ex situ X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS) to examine the surface reactions and subsequent structural and chemical evolutions of the CEI on high voltage magnesium vanadium oxide (MgV2O4) spinel cathode during the Mg2+ insertion/extraction processes. The results revealed that the presence of non-stoichiometric surface layers in the magnesium vanadium oxide cathode drive the decomposition of bis(trifluoromethanesulfonyl)imide (TFSI-) anion, leading to the formation of the CEI layer. The CEI layer could inhibit the Mg2+ ion transfer processes. Accompanying this reactivity-driven degradation, the magnesium vanadium oxide cathode undergoes pulverization, forming clusters of nanosized particles. This process likely improves cycling ability by creating new intercalation sites and shortening the diffusion pathway for the Mg2+ cations. This study demonstrates that controlling surface stoichiometry and engineering morphological properties are critical design parameters for high performance cathodes for multivalent batteries.

Molecular evolution and functional diversification of metal tolerance protein families in cereals plants and function of maize MTP protein

Plants employ metal tolerance proteins (MTPs) to confer tolerance by sequestering excess ions into vacuoles. MTPs belong to the cation diffusion facilitator (CDF) family, which facilitates the transport of divalent transition metal cations. In this study, we conducted a comprehensive analysis of the MTP gene families across 21 plant species, including maize (Zea mays). A total of 247 MTP genes were identified within these plant genomes and categorized into distinct subgroups, namely Zn-CDF, Mn-CDF, and Fe/Zn-CDF, based on phylogenetic analyses. This investigation encompassed the characterization of genomic distribution, gene structures, cis-regulatory elements, collinearity relationships, and gene ontology functions associated with MTPs. Transcriptomic analyses unveiled stress-specific expression patterns of MTP genes under various abiotic stresses. Moreover, quantitative RT-PCR assays were employed to assess maize MTP gene responses to diverse heavy metal stress conditions. Functional validation of metal tolerance roles was achieved through heterologous expression in yeast. This integrated evolutionary scrutiny of MTP families in cereals furnishes a valuable framework for the elucidation of MTP functions in subsequent studies. Notably, the prioritized MTP gene ZmMTP6 emerged as a positive regulator of plant Cd tolerance, thereby offering a pivotal genetic asset for the development of Cd-tolerant crops, particularly maize cultivars.

Electric field/current enhanced grain growth behavior of 8mol% Y2O3 stabilized cubic ZrO2 (8Y-CSZ) polycrystals

The effect of the flash event on grain growth behavior was examined in 8 mol% yttria-stabilized cubic zirconia (8Y-CSZ) polycrystals under direct and alternating electric fields/currents. Even at the same specimen temperature, the rate of the grain growth is accelerated in the flash event than in the heat treatment without electric field/current (0 V), suggesting that the non-thermal effect caused additionally under the flash event contributes to the acceleration of the grain growth. Although the grain growth behavior can be characterized by the empirical equation (dtn –d0n = kt) with the same grain growth exponent of n = 3 irrespective of the electric field/current, the activation energy for the grain growth is lowered under the flash event. This suggests that the non-thermal effect caused by the flash event does not affect the mechanism of the grain growth, but would accelerate the rate-controlling process of the grain growth. The non-thermal effects can be further accelerated in fine-grained specimens under the alternating current flash and/or by increasing the input power density. Since the grain growth is rate-controlled by the grain boundary cation diffusivity, the non-thermal effect under the flash event would accelerate the grain boundary cation diffusivities through the formation of excess oxygen vacancies depending on the polarity and the power density.

High-performance lithium batteries achieved by electrospun MXene-Enhanced cation-selective membranes

Conventional separators applied in lithium batteries face limitations like low porosity, poor electrolyte wettability, lower cation selectivity, and thermal instability, which impact battery performance and safety characteristics. Besides the challenge in separator design, transition metal ion migration from positive electrodes during cycling greatly accelerates capacity fading because of unrestricted diffusion of transition metal cation across the separator. This study explores an innovative strategy for the separator design by incorporating MXene (spraying MXene solution on both sides of the separator), a two-dimensional material, into electrospun Polyacrylonitrile/Polyetherimide membranes with the function of cation selection. Li+ can be accelerated, and its transference number increases along with the anion limitation in the MXene layer. Ni, Co, and Mn ion dissolution from the positive electrode is inhibited due to the cation selectivity of the MXene layer. Leveraging electrospinning advantages, the resultant membranes exhibit high porosity, excellent liquid absorption, mechanical strength, and superior thermal properties. Benefiting from MXene's layered structure and excellent adsorption ability, the membrane significantly inhibits the dissolution of transition metal ions while enabling smooth lithium deposition due to its cation selectivity. Eventually, the Li||NMC811 batteries deliver outstanding cyclic performance (91.3 % capacity retention after 200 cycles) and robust lithium dendrite suppression (800 h of stable cycling). Moreover, the MXene-modified membrane demonstrates exceptional electrolyte wettability, significantly improving ionic transference number (0.67) and conductivity (1.6 mS/cm). Modification of membrane surfaces with MXene offers insights into addressing transition metal ion migration from the positive electrode material perspective, providing a promising avenue for high-performance LIBs.

A Membrane-Free Rechargeable Seawater Battery Unlocked by Lattice Engineering.

Seawater batteries that directly utilize natural seawater as electrolytes are ideal sustainable aqueous devices with high safety, exceedingly low cost, and environmental friendliness. However, the present seawater batteries are either primary batteries or rechargeable half-seawater/half-nonaqueous batteries because of the lack of suitable anode working in seawater. Here, a unique lattice engineering to unlock the electrochemically inert anatase TiO2 anode to be highly active for the reversible uptake of multiple cations (Na+, Mg2+, and Ca2+) in aqueous electrolytes is demonstrated. Density functional theory calculationsfurther reveal the origin of the unprecedented charge storage behaviors, which can be attributed to the significant reduction of the cations diffusion barrier within the lattice, i.e., from 1.5 to 0.4eV. As a result, the capacities of anatase TiO2 with 2.4% lattice expansion are ≈100 times higher than the routine one in natural seawater, and ≈200 times higher in aqueous Na+ electrolyte. The finding will significantly advance aqueous seawater energy storage devices closer to practical applications.

Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure.

Exploration of compositional disorder using conventional diffraction-based techniques is challenging for systems containing isoelectronic ions possessing similar coherent neutron scattering lengths. Here, we show that a multinuclear solid-state Nuclear Magnetic Resonance (NMR) approach provides compelling insight into the Ga3+/Ge4+ cation distribution and oxygen anion transport in a family of solid electrolytes with langasite structure and La3Ga5-xGe1+xO14+0.5x composition. Ultrahigh field 71Ga Magic Angle Spinning (MAS) NMR experiments acquired at 35.2 T offer striking resolution enhancement, thereby enabling clear detection of Ga sites in different coordination environments. Three-connected GaO4, four-connected GaO4 and GaO6 polyhedra are probed for the parent La3Ga5GeO14 structure, while one additional spectral feature corresponding to the key (Ga,Ge)2O8 structural unit which forms to accommodate the interstitial oxide ions is detected for the Ge4+-doped La3Ga3.5Ge2.5O14.75 phase. The complex spectral line shapes observed in the MAS NMR spectra are reproduced very accurately by the NMR parameters computed for a symmetry-adapted configurational ensemble that comprehensively models site disorder. This approach further reveals a Ga3+/Ge4+ distribution across all Ga/Ge sites that is controlled by a kinetically governed cation diffusion process. Variable temperature 17O MAS NMR experiments up to 700 °C importantly indicate that the presence of interstitial oxide ions triggers chemical exchange between all oxygen sites, thereby enabling atomic-scale understanding of the anion diffusion mechanism underpinning the transport properties of these materials.

Influence of cationic vacancy diffusion on the aging behavior of low-temperature SrCo1-xRuxO3 thermosensitive ceramics

The thermosensitive ceramics of negative temperature coefficient (NTC), SrCo1-xRuxO3 (0 ≤ x ≤ 0.8), were synthesized using the solid-phase method. The research systematically explored the phase structure, microstructure, elemental chemical states, electrical properties, and aging performance. X-ray diffraction (XRD) data indicates that with the increase of Ru content, the lattice parameter increases. Scanning electron microscopy (SEM) images reveal a dense and uniform microstructure. X-ray photoelectron spectroscopy (XPS) data indicates the presence of Co2+/Co3+ and Ru4+/Ru5+ ion pairs. Resistive temperature data indicates its potential use as a low-temperature thermosensitive resistance material in the range of 2–300 K. Fitting the resistance-temperature curve using the thermally activated band conduction model and Mott's 3D variable range hopping model. Proposed the Ru–O2--Co hopping model, elucidating the hole hopping transport mechanism in NTC ceramics. Impedance spectroscopy analysis indicates that grain boundary resistance dominates the overall resistance of the sample. After aging at 77 K for 864 h, the maximum aging drift rate of the ceramic material is 1.55 %. Proposed a novel cationic vacancy diffusion model to explain aging phenomena, offering a new perspective for designing high-stability low-temperature NTC thermistors.

Exhaustive Study of Electrical Conductivity in the MNb2−x TixO6–0.5x (M = Mg, Ca, Zn; x = 0, 0.1, 0.2) Columbites

The CaNb2O6 and ZnNb2O6 columbites (Sp.gr. Pbcn) were studied as oxygen ion conductors both theoretically and experimentally. A theoretical approach included geometrical-topological analysis, bond valence site energy (BVSE) and density functional theory (DFT) calculations. The BVSE approach showed the possibility of pure oxygen ions diffusion with migration energies less than 0.45 eV in both compounds. However, DFT calculations indicated the possibility of diffusion of both anions and cations. The single-phases columbites were synthesized by the Pechini method for accurately determine charge carriers type and investigated by impedance spectroscopy, by the Tubandt method, which confirmed the absence of cationic conductivity, and measured the electrical conductivity as a function of oxygen partial pressures. The CaNb2O6 sample was characterized by the pure oxygen-ionic conductivity ∼2 × 10−6 S cm–1 at 800 °C (E a = 0.82 eV), while the ZnNb2O6 had a similar conductivity value due to mixed ionic-electronic contribution (E a = 0.83 eV). The electromotive force method also showed the predominance of the ionic type of conductivity in CaNb2O6, while ZnNb2O6 has a mixed conductivity with ion transport number of about 0.4. Additionally, we synthesized Ti-doped samples MNb2−x Ti x O6–0.5x (M = Mg, Ca; x = 0.1, 0.2) to study the doping effect on conducting properties.

Study on the mechanism of interaction between cations and the surface of nano-SiO2 particle in the salt solution by using molecular dynamics simulation

Nano-SiO2 solution has great potential for application in the field of oil and gas exploration and development. However, its application is restricted due to the aggregation of nano-SiO2 in stratum water. This paper studies the process of interaction between nano-SiO2 particles and salt solutions by using the molecular dynamics simulation experiments, including the characteristics of transportation and diffusion of cations around the nano SiO2, the effect of cations on the recombination and destruction of hydrogen bonds, the interaction energy between cations and nano SiO2. The main results are as follows. During the transportation and diffusion of cations in the solution, the hydrogen bonds of water molecules are broken, so that the hydrogen bonds can be rearranged, and a stable solvated layer can be formed. In the solvated layer, the repulsive force of solvation can prevent the charge exchange between cation and the charged surface of nano SiO2 particle. Compared with the monovalent salt solution, more divalent cations can break through the solvation layer to generate the charge exchange on the surface of nano-SiO2 particle. More divalent cations can conduct small amplitude oscillation movement near the surface of nano-SiO2 particle due to the strong electrostatic effect. When the concentration of salt solution is increased (3000 mg/L → 7000 mg/L) and the valence of cations is increased (monovalent → bivalent), the hydrogen bond is easier to break through the solvation layer to gather on the surface of nano SiO2 particles, which is unfavorable to the stability of nano SiO2 particles. When the cations transport to the position of 7 Å away from the surface of nano-SiO2 particles, the short-range force (including hydrogen bond force, van der Waals force, and electrostatic force) begins to affect the movement of cations. When the cations transport to the position of 2 ∼ 3 Å away from the surface of nano-SiO2 particles, the charge exchange occurs between cations and the surface of nano SiO2 particle, so that the local energy is increased and the cation continues to oscillate. In summary, with the increasing of concentration of salt solution and the valence state, more cations can break through the solvation layer to be adsorbed on the surface of nano SiO2 particle, showing that the ability of transportation and diffusion of cations is weakened, the interaction energy between nano SiO2 particle and salt solution molecules is enhanced. The electrostatic force is the main force to destroy the stability of nano SiO2 particle. The conclusions can provide a certain theoretical basis for the efficient application of nano-SiO2 materials in the field of oil and gas exploration and development and other interrelated industry.

Intervalence Charge Transfer in Aluminum Oxide and Aluminosilicate Minerals at Elevated Temperatures

Abstract Single-crystal optical spectra of corundum (Al2O3) and the Al2SiO5 polymorphs andalusite, kyanite, and sillimanite, containing both Fe2+ – Fe3+ and Fe2+ – Ti4+ intervalence charge transfer (IVCT) absorption bands were measured at temperatures up to 1000 °C. Upon heating, thermally equilibrated IVCT bands significantly decreased in intensity and recovered fully on cooling. These trends contrast with the behavior of crystal field bands at temperature for Fe, Cr and V in corundum, kyanite, and spinel. The effects of cation diffusion and aggregation, as well as the redistribution of band intensity at temperature, are also discussed. The loss of absorption intensity in the visible and near-infrared regions of the spectrum of these phases may point to a more general behavior of IVCT in minerals at temperatures within the Earth with implications for radiative conductivity within the Earth.

Designing a Magnesium/Sodium Hybrid Battery Using Hierarchical Iron Selenide Architecture as Cathode Material and Modified Dual-Ion Salts in Ether as Electrolyte.

We developed a magnesium/sodium (Mg/Na) hybrid battery using a hierarchical disk-whisker FeSe2 architecture (HD-FeSe2) as the cathode material and a modified dual-ion electrolyte. The polarizable Se2- anion reduced the Mg2+ migration barrier, and the 3D configuration possessed a large surface area, which facilitated both Mg2+/Na+ cation diffusion and electron transport. The dual-ion salts with NaTFSI in ether reduced the Mg plating/stripping overvoltage in a symmetric cell. The hybrid battery exhibited an energy density of 260.9 Wh kg-1 and a power density of 600.8 W kg-1 at 0.2 A g-1. It showed a capacity retention of 154 mAh g-1 and a Coulombic efficiency of over 99.5% under 1.0 A g-1 after 800 long cycles. The battery also displayed outstanding temperature tolerance. The findings of 3D architecture as cathode material and hybrid electrolyte provide a pathway to design a highly reliable Mg/Na hybrid battery.

Development of a physical reservoir that operates by the diffusion of Cu cations

We developed a physical reservoir using Cu2S and Cu-doped Ta2O5 as a material of a reservoir layer, in both of which Cu cations contribute to the reservoir operation. The reservoirs showed nonlinearity and short-term memory required as reservoirs. The memory capacity becomes maximum with the input frequency at around 104 Hz. The t-distributed stochastic neighbor embedding analysis revealed that a Cu2S reservoir can classify input of five bit pulse trains, and a Cu-doped Ta2O5 reservoir can classify input of six bit pulse trains. These are longer than four bit pulse trains that a Ag2S island network reservoir achieved in our previous study. Using the superior performance, NARMA task was also carried out.

Enhanced Li+ and Mg2+ Diffusion at the Polymer–Ionic Liquid Interface within PVDF‐Based Ionogel Electrolytes for Batteries and Metal‐Ion Capacitors

AbstractWith the widespread use of batteries, their increased performance is of growing in importance. One avenue for this is the enhancement of ion diffusion, particularly for solid‐state electrolytes, for different ions such as lithium (Li+) and magnesium (Mg2+). Unraveling the origin of better cation diffusion in confined ionic liquids (ILs) in a polymer matrix (ionogels) is compared to that of the IL itself. Ionic conductivity measured by electrochemical impedance spectroscopy for ionogels (7.0 mS cm−1 at 30 °C) is very close to the conductivity of the non‐confined IL (8.9 mS cm−1 at 30 °C), that is, 1‐ethyl‐3‐methyimidazolium bis(trifluorosulfonyl)imide (EMIM TFSI). An even better ionic conductivity is observed for confined EMIM TFSI with high concentrations (1 m) of lithium or magnesium salt added. The improved macroscopic transport properties can be explained by the higher self‐diffusion of each ion at the liquid‐to‐solid interface induced by the confinement in a poly‐vinylidenedifluoride (PVDF) polymer matrix. Upon confinement, the strong breaking down of ion aggregates enables a better diffusion, especially for TFSI anion and strongly polarizing cations (e.g., Li+, Mg2+.). The coordination number of these cations in the liquid phase confirmed that Li+ and Mg2+ interact with the polymer matrix. Moreover, it is a major result that the activation energy for diffusion is lowered.

Influence of magnetic field upon electrode kinetics and ionic transport

Performance properties in lithium-ion, sodium-ion, and zero excess metal batteries are currently limited by the sluggish ion diffusion and inhomogeneity of the transport ion flux, resulting in poor formation, low rates, and short cycle lives. In this work, a magnetic field is applied to the cell by the incorporation of a NdFeB magnetic spacer, and the effect upon the kinetics and transport properties at each electrode is studied using galvanic charge and discharge, electrochemical impedance spectroscopy, and intermittent titration techniques. Stabilization of the anode-free or zero excess sodium and lithium metal cells is achieved during formation, and upon cycling. Reduced cell overpotential is observed with resulting higher areal capacities, with improved ionic diffusion through the electrode. Upon cycling metallic dendritic structures are suppressed due to the inhomogeneity of ion flux, and the likely competing kinetics of plating at a metallic tip and the surrounding surface. At the NMC electrode, improved kinetics are observed with lower charge-transfer resistance (Rct) due to the reshaped and aligned domain in the ferromagnetic Ni of NMC cathode. Pulsed current methods further confirm enhanced cationic diffusion in the anode graphite materials, particularly at high mass loading of 4 mA h cm−2 and high C rates. Consequently, the combination of enhanced reaction kinetics on the ferromagnetic cathode and improved diffusion kinetics in the porous anode leads to excellent full-cell performance compared to control groups. This study highlights the potential of magnetic fields in enhancing diffusion and reaction kinetics for rechargeable batteries (Li, Na, K, Mg, etc.), and may provide routes for extending cycle life, reconditioning cells, and improving formation protocols.

Designing Atomic Interface in Sb2S3/CdS Heterojunction for Efficient Solar Water Splitting.

In the emerging Sb2S3-based solar energy conversion devices, a CdS buffer layer prepared by chemical bath deposition is commonly used to improve the separation of photogenerated electron-hole pairs. However, the cation diffusion at the Sb2S3/CdS interface induces detrimental defects but is often overlooked. Designing a stable interface in the Sb2S3/CdS heterojunction is essential to achieve high solar energy conversion efficiency. As a proof of concept, this study reports that the modification of the Sb2S3/CdS heterojunction with an ultrathin Al2O3 interlayer effectively suppresses the interfacial defects by preventing the diffusion of Cd2+ cations into the Sb2S3 layer. As a result, a water-splitting photocathode based on Ag:Sb2S3/Al2O3/CdS heterojunction achieves a significantly improved half-cell solar-to-hydrogen efficiency of 2.78% in a neutral electrolyte, as compared to 1.66% for the control Ag:Sb2S3/CdS device. This work demonstrates the importance of designing atomic interfaces and may provide a guideline for the fabrication of high-performance stibnite-type semiconductor-based solar energy conversion devices.

One-Step Hydrothermal Synthesis of NVO Cathodes with Varied Lattice NH4 + Content: Effect on Structural Evolution and Electrochemical Performance.

Aqueous zinc ion batteries have been extensively researched due to their distinctive advantages such as low cost and high safety. Vanadium oxides are important cathode materials, however, poor cycle life caused by vanadium dissolution limits their application. Recent studies show that the lattice NH4 + in vanadium oxides can act as a pillar to enhance structural stability and play a crucial role in improving its cycling stability. Nevertheless, there is still a lack of research on the effect of the lattice NH4 + content on structural evolution and electrochemical performance. Herein, we synthesize vanadium oxides with different contents of lattice NH4 + by a one-step hydrothermal reaction. The vanadium oxides with lattice NH4 + exhibit high initial capacity, as well as good cycling stability and rate performance compared to bare vanadium oxide. Combined with electrochemical analyses, ex-situ structural characterizations, and in-situ X-ray diffraction tests, we reveal that the lattice NH4 + content plays a positive role in vanadium oxides' structural stability and cation diffusion kinetics. This work presents a direction for designing high-performance vanadium cathodes for aqueous zinc ion batteries.

Isotope fractionation of alkaline and alkaline-earth elements (Li, K, Rb, Mg, Ca, Sr, Ba) during diffusion in aqueous solutions

In this study, we used an improved “diffusion cell” method to precisely determine the diffusion-driven kinetic isotope fractionation factors of the Li, K, Rb, Mg, Ca, Sr, and Ba cations in aqueous solutions under room temperature. The obtained isotope fractionation factors (±2σ errors) are, α7/6Li = 0.996139 ± 0.000140, α41/39K = 0.998572 ± 0.000072, α87/85Rb = 0.999333 ± 0.000020, α26/24Mg = 0.999877 ± 0.000010, α44/42Ca = 0.999704 ± 0.000010, α88/86Sr = 0.999781 ± 0.000014, α138/135Ba = 0.999716 ± 0.000018. The results show that the charge of the cation and the ion-water bond length for the aquo ions are the two predominant factors affecting the mass dependence of isotope fractionation (β factor) during cation diffusion in aqueous solutions. Cations with higher charge numbers and shorter ion-water bond lengths exhibit less kinetic isotope fractionation during diffusion. Therefore, the isotope separation effect during diffusion (or β factor) in fluids is fundamentally controlled by the intensity of ion-water interaction. Weaker ion-water interaction (e.g., lower charge number, longer ion-water bond length) leads to less prominent hydrodynamic behavior for diffusing ions at the molecular level, thus more significant isotope fractionation in bulk solutions, and vice versa. Ions of larger radius would show stronger mass dependence of isotope fractionation (β factor), which can cancel the effect of decreasing relative isotope mass difference for heavier elements, thus kinetic isotope fractionation during diffusion in aqueous solutions remains prominent even for heavy elements such as Rb, Sr, and Ba. The diffusion-driven kinetic isotope fractionation factors measured in this study could provide a useful basis for interpreting specific natural isotopic variability of alkaline and alkaline-earth elements in supergene environments where chemical diffusion takes place.

Compositional zoning of the Otowi Member of the Bandelier Tuff, Valles caldera, New Mexico, USA

Abstract The Otowi Member of the Bandelier Tuff erupted at ca. 1.60 Ma from the Valles caldera (New Mexico, USA). It consists of as much as 400 km3 (dense rock equivalent) of strongly differentiated high-silica rhyolite and shows systematic upward variations in crystallinity, mineral chemistry, and trace element concentrations through its thickness, but the major element composition is almost constant and is near the low-pressure granite minimum. Incompatible trace elements in whole pumice fragments and glasses show well-correlated linear covariations. Upward zoning to lower abundances of incompatible trace elements is accompanied by development of overgrowths on quartz and alkali feldspar, although earlier-formed interiors of quartz and feldspar have near-constant compositions throughout the tuff, modified by cation diffusion in the case of feldspar. Melt inclusions in remnant quartz cores show diverse Pb isotope ratios, pointing to a wide range of distinct protoliths that contributed rhyolitic melt to the Otowi magma. Mineral thermometers suggest a modest temperature gradient through the melt body, perhaps of 40 °C, at the time of eruption. Chemical, textural, and mineralogical variations and volume-composition relations through the tuff are consistent with an origin for zoning by melting of a high-crystallinity cumulate layer beneath cognate supernatant liquid to produce denser, remobilized liquid of accumulative composition (i.e., the “modified mush model”). Melting may have occurred in several episodes. The latest of these episodes, probably thousands of years prior to eruption, introduced new rhyolitic liquid into the system and was associated with a thermal excursion, recorded in core compositions of pyroxene, during which much of the earlier crystal mass was dissolved. This left inherited cores and interiors of accumulated quartz and feldspar mantled with new growth having less-evolved compositions (higher Ti, Sr, and Ba). Changing solubility of zircon during cumulate melting produced a reversal of Zr concentrations. There is no clear petrologic evidence of a recharge eruption trigger; nonetheless, compositional zoning resulted mainly from repeated recharge-induced remobilization of quartz-feldspar cumulate. The Otowi system was built, evolved, and modified by several events over the course of a few hundred thousand years.

Forsteritic olivine in EH (enstatite) chondrite meteorites: A record of nebular, metamorphic, and crystal‐lattice diffusion effects

AbstractThe occurrence of forsteritic olivine in EH enstatite chondrites is indicative of bulk disequilibrium. In MgO‐rich magmatic systems, forsterite can either crystallize as a liquidus phase or be produced during peritectic melting of enstatite. Because diffusion of divalent cations through forsterite is relatively rapid, it records peak melting (i.e., chondrule‐forming events) and is also sensitive to subsequent metamorphism in the EH chondrite parent body. Here, we report the major and minor element geochemistry of olivine in EH chondrites across petrologic types 3 and 4. In all cases, olivine meets the technical definition of forsterite (>90 mole% Mg2SiO4). For unequilibrated EH chondrites, minor elements identify CaO‐Al2O3‐TiO2‐rich (refractory forsterite), MnO‐rich (“LIME” forsterite), and FeO‐bearing (forsteritic olivine) endmember components, the latter with Cr2O3‐rich and Cr2O3‐poor varieties. At higher petrologic type, minor element concentrations become restricted and compositions approach pure forsterite, while grain sizes reduce strongly with peak metamorphic temperatures. These changes reflect diffusive equilibration with enstatitic groundmass and dissolution reaction with free silica. The global geochemical distribution of forsteritic olivine in EH chondrites is, perhaps unexpectedly, more similar to those in low‐FeO type I chondrules and associated objects in carbonaceous chondrites (CCs), rather than equivalent objects in ordinary (H, L, LL), low‐FeO (or HH), or Kakangari (K) chondrites. Among achondrites, there is similarity between pure forsterite in aubrites and EH4 chondrites arising due to subsolidus equilibration in both settings, while Cr2O3‐poor forsteritic olivine in EH3 and CCs is similar to magnesian xenocrystic olivine in angrites. This might reflect CaO‐rich and SiO2‐poor magmatic sources across multiple early solar system reservoirs.

A high-current hydrogel generator with engineered mechanoionic asymmetry.

Mechanoelectrical energy conversion is a potential solution for the power supply of miniaturized wearable and implantable systems; yet it remains challenging due to limited current output when exploiting low-frequency motions with soft devices. We report a design of a hydrogel generator with mechanoionic current generation amplified by orders of magnitudes with engineered structural and chemical asymmetry. Under compressive loading, relief structures in the hydrogel intensify net ion fluxes induced by deformation gradient, which synergize with asymmetric ion adsorption characteristics of the electrodes and distinct diffusivity of cations and anions in the hydrogel matrix. This engineered mechanoionic process can yield 4 mA (5.5 A m-2) of peak current under cyclic compression of 80 kPa applied at 0.1 Hz, with the transferred charge reaching up to 916 mC m-2 per cycle. The high current output of this miniaturized hydrogel generator is beneficial for the powering of wearable devices, as exemplified by a controlled drug-releasing system for wound healing. The demonstrated mechanisms for amplifying mechanoionic effect will enable further designs for a variety of self-powered biomedical systems.