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Structure, electrical conductivity and electrochemical performance for a new oxygen deficient perovskite material with composition SrCo0.85Fe0.15O2.62 is explored here. It crystallizes in a '314-type' oxygen-vacancy ordered structure (Space Group: I4 /mmm) with 2ap × 2ap × 4ap unit cell, and contains alternate oxygen replete [Co2/Fe2-O] and oxygen deficient [Co1/Fe1-O] planes along c-direction. Room temperature Mössbauer spectroscopy and room temperature neutron powder diffraction confirm the presence of mixed valence states (3+ and 4+) for both Fe and Co. Polaronic behavior in the electrical conductivity is observed below 400 °C, and attributed to the presence of Co4+ and Fe3+ cations in the structure. The electrical conductivity at 600 °C is high enough (∼200 S cm−1) to act as a cathode material. At the same time, the polarization resistance measurements show an excellent value of 0.1 Ω cm2 at 600 °C. These results suggest that at 600 °C, this material is a mixed oxide-ion and electronic conductor exhibiting excellent activity for the oxygen reduction reaction, making it a promising cathode material for an intermediate temperature solid oxide fuel cell. [ABSTRACT FROM AUTHOR]

Manganese-doped ZnAl2O4 phosphors were prepared by the Pechini synthesis route and treated at various temperatures from 600 to 1350 °C. The samples were characterized by TEM-EDX, XRD, EPR, and their diffuse reflectance and luminescence properties were investigated. The structural analysis showed the high solubility limit of manganese in this spinel matrix and allowed the determination of the global inversion rate, which characterizes the cation distribution in the A and B sites of the spinel structure. As the annealing temperature increased, this factor decreased leading to a more direct matrix. EPR analysis showed that, besides Mn3+ to Mn2+ reduction, the local environment of Mn2+ cations changed with the annealing temperature, which was also reflected in the evolution of the optical properties. As the annealing temperature increased, the red luminescence related to the presence of divalent manganese in octahedral sites faded and was replaced by a new green emission due to Mn(ii) ions located in tetrahedral sites within the spinel structure. For 0.5% Mn-doped ZnAl2O4, this red to green luminescence switch occurred for samples treated between 1200 and 1350 °C. Moreover, the Al-overstoichiometric samples (Mn:ZnAl2.2O4+δ) showed that it is possible to modify the temperature range and the kinetics of this variation in emission wavelength. These tuneable properties suggest that Mn-doped spinels are potential candidates for developing stable and highly sensitive thermal sensors. [ABSTRACT FROM AUTHOR]

Obsidians from major Ecuadorian sources (outcrops) were analyzed by electron spin resonance, SQUID magnetometry and 57Fe Mössbauer spectroscopy. If the last technique allows to discriminate obsidians from the Quiscatola source, an association of ESR with SQUID magnetometry permits to differentiate obsidians from the sources of Cotopaxi volcano, from the Quiscatola and Mullumica-Callejones sources of the Chacana caldera and to infer that the 12 analyzed obsidians from the pre-Hispanic site of La Maná come from the Mullumica-Callejones source. [ABSTRACT FROM AUTHOR]

We report the results of a study on the weathering products of 21 meteorites found in the Atacama Desert (Chile) using room temperature 57Fe Mössbauer spectroscopy (MS). The meteorites are weathered ordinary chondrites (OCs) with unknown terrestrial ages and include the three chemical groups (H, L, and LL). We obtained the percentage of all the Fe-bearing phases for the primary minerals: olivine, pyroxene, troilite and Fe–Ni metal, and for the ferric alteration products (composed of the paramagnetic Fe3+ component and the magnetically ordered Fe3+ components) which gives the percentage of oxidation of the samples. From the Mössbauer absorption areas of these oxides, the terrestrial oxidation of the Atacama OC was found in the range from ~5% to ~60%. The amount of silicates as well as the opaques decreases at a constant rate with increasing oxidation level. [ABSTRACT FROM AUTHOR]

Archaeological artefacts made of obsidian are all the more precious for archaeologists as they are witnesses of cultural, social or ‘economic’ relationships between prehistoric populations. The main obsidian sources reachable in these times have been identified and characterized by chemical analysis and fission track dating. Because of iron presence (from 1% to 10% expressed in Fe2O3) it is possible to use Mo¨ssbauer spectroscopy and electron spin resonance (ESR) on geological samples to characterize different sources. We studied by electron spin resonance about seventy obsidians coming from six Mediterranean volcanic islands. The complex spectra are mainly due to iron in different states and site location (and sometimes isolated Mn2+ ions). X-band (9 GHz) spectra exhibit a signal at g=4.3 with a shoulder at 9.8 ascribed to isolated Fe3+ in the glassy matrix with a rhombic environment (C2v). Condensed clusters of Fe3+ ions give rise to a resonance line at g=2.0 whose position and width do not depend on temperature and in addition to this signal broad resonance lines are ascribed to micro-crystallites of mixed iron oxides (hematite, magnetite and related spinels, titanates, silicates) as inclusions into the amorphous matrix of obsidian. When temperature decreases from 300 to 5 K these signals shift towards weak fields. The contribution of every signal to ESR spectrum is different from one source to the other according to the different thermodynamic conditions that occurred during obsidian formation. It is thus possible to discriminate a priori one geological source using ESR spectra. At room temperature the first differences appear at X-band, low temperatures experiments may allow to remove some ambiguities. [Copyright &y& Elsevier]

Structural trends, physical properties, and electrochemical performances of the NaFe x Ru 2- x O 4 system have been investigated. Synthesis attempts using both conventional solid-state routes and high-pressure methods were explored for the compositional range 1.0 ≤ x ≤ 1.67. Based on Rietveld refinements against powder X-ray diffraction data, analyses of 57 Fe Mössbauer spectroscopy data, and elemental analysis by electron microprobe, the existence of a confined compositional solid solution (1 ≤ x ≤ 1.3) adopting the CaFe 2 O 4 -type postspinel structure is demonstrated. This is contrasted with the NaFe x Ti 2 - x O 4 system, for which no evidence of a solid solution is observed. However, for all explored synthetic routes of NaFe x Ru 2- x O 4 compositions, a trivalent iron oxidation state is maintained. Structural analysis and qualitative bond valence energy landscape models reveal that the progressive integration of iron into the postspinel framework results in narrowed sodium ion diffusion channels, restricting electrochemical deintercalation of sodium. Consequently, the CaFe 2 O 4 -type iron-rich compounds explored in this study demonstrate limited potential as positive electrode materials for sodium batteries. It is expected that this fundamental insight will help guide the exploration of alternative NaM 2 O 4 -based positive electrode materials with similar structure types.

Silicate-based bioactive glass nano/microspheres hold significant promise for bone substitution by facilitating osteointegration through the release of biologically active ions and the formation of a biomimetic apatite layer. Cu-doping enhances properties such as pro-angiogenic and antibacterial behavior. While sol-gel methods usually yield homogeneous spherical particles for pure silica or binary glasses, synthesizing poorly aggregated Cu-doped ternary glass nano/microparticles without a secondary CuO crystalline phase remains challenging. This article introduces an alternative method for fabricating Cu-doped ternary microparticles using sol-gel chemistry combined with spray-drying. The resulting microspheres exhibit well-defined, poorly aggregated particles with spherical shapes and diameters of a few microns. Copper primarily integrates into the microspheres as Cu 0 nanoparticles and as Cu 2+ within the amorphous network. This doping affects silica network connectivity, as calcium and phosphorus are preferentially distributed in the glass network (respectively as network modifiers and formers) or involved in amorphous calcium phosphate nano-domains depending on the doping rate. These differences affect the interaction with simulated body fluid. Network depolymerization, ion release (SiO 4 4- , Ca 2+ , PO 4 3- , Cu 2+ ), and apatite nanocrystal layer formation are impacted, as well as copper release. The latter is mainly provided by the copper involved in the silica network and not from metal nanoparticles, most of which remain in the microspheres after interaction. This understanding holds promising implications for potential therapeutic applications, offering possibilities for both short-term and long-term delivery of a tunable copper dose. STATEMENT OF SIGNIFICANCE: A novel methodology, scalable to industrial levels, enables the synthesis of copper-doped ternary bioactive glass microparticles by combining spray-drying and sol-gel chemistry. It provides precise control over the copper percentage in microspheres. This study explores the influence of synthesis conditions on the copper environment, notably Cu 0 and Cu 2+ ratios, characterized by EPR spectroscopy, an aspect poorly described for copper-doped bioactive glass. Additionally, copper indirectly affects silica network connectivity and calcium/phosphorus distribution, as revealed by SSNMR. Multiscale characterization illustrates how these features impact acellular degradation in simulated body fluid, highlighting the therapeutic potential for customizable copper dosing to address short- and long-term needs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

We report the synthesis of WO 3 , TiO 2 , and TiO 2 -WO 3 nanoparticles by a polyol route, with the objective of studying the influence of the preparation method on their photochromic properties. By combining transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and diffuse reflectance experiments, we show that low W 6+ concentrations and high ripening temperatures allow the preparation of WO 3 nanoparticles with high photochromic efficiency. WO 3 -TiO 2 nanocomposites (NCs) prepared by the introduction of a TiO 2+ solution in a WO 3 nanoparticle suspension exhibit a strong coloring photochromism, which is attributed to the TiO 2 coating of the WO 3 nanoparticles as it involves the formation of W-O-Ti oxo-bonds in place of W 5+ -ν O defects. Especially, after an oxidative treatment in order to obtain an initial pale-yellow material, such WO 3 -TiO 2 NCs exhibit a fully reversible photochromism with a large contrast between the colored and bleached state. They could therefore be incorporated in hybrid smart films for solar control on building window glasses. On the other hand, while the WO 3 -TiO 2 NCs are functionalized with DPA (n-dodecyl phosphonic acid), the as-prepared nanocomposites exhibit exacerbated coloring contrast but with a nearly nonreversible photochromism (very limited bleaching), which makes them good candidates for the fabrication of smart UV-sensor devices that can indicate the cumulative UV dose which is received.

Introducing compositional or structural disorder within crystalline solid electrolytes is a common strategy for increasing their ionic conductivity. (M,Sn)F 2 fluorites have previously been proposed to exhibit two forms of disorder within their cationic host frameworks: occupational disorder from randomly distributed M and Sn cations and orientational disorder from Sn(II) stereoactive lone pairs. Here, we characterize the structure and fluoride-ion dynamics of cubic BaSnF 4 , using a combination of experimental and computational techniques. Rietveld refinement of the X-ray diffraction (XRD) data confirms an average fluorite structure with {Ba,Sn} cation disorder, and the 119 Sn Mössbauer spectrum demonstrates the presence of stereoactive Sn(II) lone pairs. X-ray total-scattering PDF analysis and ab initio molecular dynamics simulations reveal a complex local structure with a high degree of intrinsic fluoride-ion disorder, where 1/3 of fluoride ions occupy octahedral "interstitial" sites: this fluoride-ion disorder is a consequence of repulsion between Sn lone pairs and fluoride ions that destabilizes Sn-coordinated tetrahedral fluoride-ion sites. Variable-temperature 19 F NMR experiments and analysis of our molecular dynamics simulations reveal highly inhomogeneous fluoride-ion dynamics, with fluoride ions in Sn-rich local environments significantly more mobile than those in Ba-rich environments. Our simulations also reveal dynamical reorientation of the Sn lone pairs that is biased by the local cation configuration and coupled to the local fluoride-ion dynamics. We end by discussing the effect of host-framework disorder on long-range diffusion pathways in cubic BaSnF 4 .

Sr 2 FeO 3 F, an oxyfluoride compound with an n = 1 Ruddlesden-Popper structure, was identified as a potential interesting mixed ionic and electronic conductor (MIEC). The phase can be synthesized under a range of different p O 2 atmospheres, leading to various degrees of fluorine for oxygen substitution and Fe 4+ content. A structural investigation and thorough comparison of both argon- and air-synthesized compounds were performed by combining high-resolution X-ray and electron diffraction, high-resolution scanning transmission electron microscopy, Mössbauer spectroscopy, and DFT calculations. While the argon-synthesized phase shows a well-behaved O/F ordered structure, this study revealed that oxidation leads to averaged large-scale anionic disorder on the apical site. In the more oxidized Sr 2 FeO 3.2 F 0.8 oxyfluoride, containing 20% of Fe 4+ , two different Fe positions can be identified with a 32%/68% occupancy ( P 4/ nmm space group). This originates due to the presence of antiphase boundaries between ordered domains within the grains. Relations between site distortion and valence states as well as stability of apical anionic sites (O vs F) are discussed. This study paves the way for further studies on both ionic and electronic transport properties of Sr 2 FeO 3.2 F 0.8 and its use in MIEC-based devices, such as solid oxide fuel cells.

Since its discovery, electrochromism, known as the modulation of optical properties under an applied voltage, has attracted strong interest from the scientific community and has proved to be of significant utility in various applications. Although vanadium dioxide (VO 2 ) has been a candidate for extensive research for its thermochromic properties, its intrinsic electrochromism has scarcely been reported so far. In this study, multi-electrochromism is described for VO 2 thick films. Indeed, a VO 2 opaque film, doctor bladed from homemade monoclinic VO 2 powder, shows a pronounced color modulation from orange to green and blue associated with an amorphization-recrystallization phenomenon upon cycling in a lithium-based electrolyte. The strong memory effect allows us to follow the coloration mechanism by combining various ex situ and in situ characterizations addressing both structural and electronic aspects. Upon cycling, the multichromism of VO 2 finds its origin in the transformation of VO 2 into orange V 2 O 5 upon oxidation, while in reduction, the blue lithiated state illustrates a mixed vanadium oxidation state.

In this fundamental solid-state chemistry study, two sample series were investigated in depth: iron(III)-doped hydroxyapatite (HA) compounds obtained from a co-sintering process of hematite and pure HA under air and iron(III)-doped HA compounds obtained from a co-sintering process from iron(II) acetate and pure HA under an argon atmosphere. X-ray diffraction, UV-visible, Fourier transform infrared, 1 H and 31 P NMR, electron paramagnetic resonance (EPR,) and Mössbauer spectroscopy methods were coupled to unravel the Fe valence states, the interactions with other anionic species (OH - and PO 4 3- ), and finally the complex local environments in hexagonal channels in both the series. In particular, we highlighted the associated mechanism to ensure electroneutrality with a focus on deprotonation versus calcium substitution. By diverging mechanisms, Fe 3+ and Fe 2+ ions were found to be located in different coordinated sites: 4(+1) coordinated site for Fe 3+ and 2(+3) coordinated site for Fe 2+ and clearly associated with very different Mössbauer and EPR signatures as various absorption bands (leading to different sample colors).

Magnetic nanoparticles are central to the development of efficient hyperthermia treatments, magnetic drug carriers, and multimodal contrast agents. While the magnetic properties of small crystalline iron oxide nanoparticles are well understood, the superparamagnetic size limit constitutes a significant barrier for further size reduction. Iron (oxy)hydroxide phases, albeit very common in the natural world, are far less studied, generally due to their poor crystallinity. Templating ultrasmall nanoparticles on substrates such as graphene is a promising method to prevent aggregation, typically an issue for both material characterization and applications. We generate ultrasmall nanoparticles, directly on the carbon framework by the reaction of a graphenide potassium solution, charged graphene flakes, with iron(II) salts. After mild water oxidation, the obtained composite material consists of ultrasmall potassium ferrite nanoparticles bound to the graphene nanoflakes. Magnetic properties as evidenced by magnetometry and X-ray magnetic circular dichroism, with open magnetic hysteresis loops near room temperature, are widely different from classical ultrasmall superparamagnetic iron oxide nanoparticles. The large value obtained for the effective magnetic anisotropy energy density K eff accounts for the presence of magnetic ordering at rather high temperatures. The synthesis of ultrasmall potassium ferrite nanoparticles under such mild conditions is remarkable given the harsh conditions used for the classical syntheses of bulk potassium ferrites. Moreover, the potassium incorporation in the crystal lattice occurs in the presence of potassium cations under mild conditions. A transfer of this method to related reactions would be of great interest, which underlines the synthetic value of this study. These findings also give another view on the previously reported electrocatalytic properties of these nanocomposite materials, especially for the sought-after oxygen reduction/evolution reaction. Finally, their longitudinal and transverse proton NMR relaxivities when dispersed in water were assessed at 37 °C under a magnetic field of 1.41 T, allowing potential applications in biological imaging.

Sodium-rich iron hexacyanoferrates were prepared by coprecipitation, hydrothermal route, and under reflux, with or without dehydration. They were obtained with different structures described in cubic, orthorhombic, or rhombohedral symmetry, with variable compositions in sodium, water, and cationic vacancies and with a variety of morphologies. This series of sodium-rich Prussian blue analogues allowed addressing the relationship between synthesis conditions, composition, structure, morphology, and electrochemical properties in Na-ion batteries. A new orthorhombic phase with the Na 1.8 Fe 2 (CN) 6 ·0.7H 2 O composition synthesized by an hydrothermal route at 140 °C is reported for the first time, whereas a phase of Na 2 Fe 2 (CN) 6 ·2H 2 O composition obtained under reflux, previously described with a monoclinic structure, shows in fact a rhombohedral structure.

Atherosclerosis is at the onset of the cardiovascular diseases that are among the leading causes of death worldwide. Currently, high-risk plaques, also called vulnerable atheromatous plaques, remain often undiagnosed until the occurrence of severe complications, such as stroke or myocardial infarction. Molecular imaging agents that target high-risk atheromatous lesions could greatly improve the diagnosis of atherosclerosis by identifying sites of high disease activity. Moreover, a "theranostic approach" that combines molecular imaging agents (for diagnosis) and therapeutic molecules would be of great value for the local management of atheromatous plaques. The aim of this study was to develop and characterize an innovative theranostic tool for atherosclerosis. We engineered oil-in-water nano-emulsions (NEs) loaded with superparamagnetic iron oxide (SPIO) nanoparticles for magnetic resonance imaging (MRI) purposes. Dynamic MRI showed that NE-SPIO nanoparticles decorated with a polyethylene glycol (PEG) layer reduced their liver uptake and extended their half-life. Next, the NE-SPIO-PEG formulation was functionalized with a fully human scFv-Fc antibody (P3) recognizing galectin 3, an atherosclerosis biomarker. The P3-functionalized formulation targeted atheromatous plaques, as demonstrated in an immunohistochemistry analyses of mouse aorta and human artery sections and in an Apoe -/- mouse model of atherosclerosis. Moreover, the formulation was loaded with SPIO nanoparticles and/or alpha-tocopherol to be used as a theranostic tool for atherosclerosis imaging (SPIO) and for delivery of drugs that reduce oxidation (here, alpha-tocopherol) in atheromatous plaques. This study paves the way to non-invasive targeted imaging of atherosclerosis and synergistic therapeutic applications.

ZnO/MoO 3 powder mixture exhibits a huge photochromic effect in comparison with the corresponding single oxides. The coloring efficiency of such combined material after UV-light irradiation was studied in terms of intensity, kinetics, and ZnO/MoO 3 powder ratio. Additionally, the incidence of the pretreatment step of the ZnO and MoO 3 powders under different atmospheres (air, Ar or Ar/H 2 flow) was analyzed. The huge photochromic effect discovered herein was interpreted as the creation of "self-closed Schottky barrier" at the solid/solid interfaces between the two oxides, associated with the full redox reaction which can be pictured by the equation ZnO 1-ε + MoO 3 → ZnO + MoO 3-ε . Remarkable optical contrast between virgin and color states as well as self-bleaching in dark allowing the reversibility of the photochromism is emphasized. From this first discovery, deeper characterization of the self-bleaching process shows that the photochromic mechanism is complex with a bleaching efficiency (possibility to come back to the virgin material optical properties without any deterioration) and a bleaching kinetics, which are both dependent on the coloring irradiation time. This demonstrates that the oxygen exchange through the Schottky interface proceeds in at least two convoluted steps: an anionic surface exchange allowing a reversibility of the redox reaction followed by bulk diffusion of the exchanged anions which are then definitively trapped. An emergent "negative photochromism effect" (i.e., photochromism associated with a self-bleaching instead of a darkening under irradiation) is observed after a long irradiation time.