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Feiite (Fe3TiO5) is a high-pressure Fe-Ti oxide mineral recently discovered in martian meteorite Shergotty. Feiite is isostructural with Fe4O5, a high-pressure iron oxide stable at pressures >10 GPa. The stability of feiite has yet to be studied, as it has not previously been synthesized in the laboratory. To determine the minimum pressure at which feiite can be synthesized, we have conducted multi-anvil experiments at 1200 °C and at pressures ranging from 7 to 12 GPa. Major element compositions and XRD patterns indicate that we successfully synthesized feiite with an orthorhombic unit cell (Cmcm structure) in experiments conducted at pressures 8 GPa or greater. Relative to A2B2O5 phases with similar structure, feiite can be synthesized at lower pressures. The coexistence of feiite and liuite (FeTiO3-perovskite) in Shergotty indicates that the upper pressure limit of feiite stability is above 15 GPa. To investigate the effect of oxygen fugacity on the composition and stability of feiite, we conducted an additional series of experiments at 1200 °C and 10 GPa pressure in which we varied the Fe3+/Fetotal ratio of the experimental starting materials. In doing so, we identified a minimum Fe3+ content necessary to stabilize the feiite structure (Fe3+/Fetotal = 0.26 at 10 GPa and 1200 °C). The importance of Fe3+ for feiite stability suggests this phase would not form in lunar or HED meteorites, where iron-titanium oxides contain little to no ferric iron. Though our experimental results can only place a lower limit on the shock pressures experienced in Shergotty, the determined pressure stability indicates feiite could also be present in diamond-bearing terrestrial rocks sourced from the upper mantle or transition zone. Additionally, the presence of feiite would be an indicator of source Fe3+/ Fetotal. [ABSTRACT FROM AUTHOR]

The scientific community is inclined towards addressing environmental and energy concerns through sustainable means. Conventional processes such as chemical synthesis, involve the usage of environmentally harmful ligands and high tech facilities, which are time-consuming, expensive, energy-intensive, and require extreme conditions for synthesis. Plant-based synthesis is valuable and sustainable for the ecosystem. The use of plant-based precursors for nanoparticle synthesis eliminates the menace of toxic waste contamination. The present review elucidates that the plant based synthesized iron oxide and manganese oxide nanoparticles have tremendous and exceptional applications in various fields such as antimicrobial and antioxidative domains, environmental, electrical and sensing properties. Hence, the literature reviewed explains that plant based synthesis of nanoparticles is an adept and preferred technique. These important transition oxide metal nanoparticles have great applicability in ecological, environmental science as well as electrochemistry and sensing technology. Both these metal oxides display a stable and adaptable nature, which can be functionalized for a specific application, thus exhibiting great potential for efficiency. The current review epitomizes all the latest reported work on the synthesis of iron and manganese oxide nanoparticles through a greener approach along with explaining various significant applications keeping in view the concept of sustainability. [ABSTRACT FROM AUTHOR]

Short-range-ordered Fe(III) minerals such as ferrihydrite (Fh) are ubiquitous in the environment, are key players in biogeochemical cycling, and sorb trace elements and nutrients. As such, it is important to be able to identify the presence of such minerals in natural samples. Fh is commonly observed to be X‑ray amorphous and cannot be easily analyzed using X‑ray diffraction, meaning that spectroscopic methods such as X‑ray absorption or 57Fe Mössbauer spectroscopy (MBS) are necessary for accurate identification and quantification. Despite decades of research into Fh using MBS, there is a discrepancy in the literature about the exact parameters applicable to the mineral when measured at liquid helium temperature. Fh is frequently fitted with either one, two, or three hyperfine sextets with little interpretation applied to the meaning of each, which is problematic as a one sextet model does not account for the asymmetric lineshape frequently observed for Fh. Here, we address inconsistencies in the fitting of Fh and provide a more standardized approach to its identification by MBS. We present a systematic comparison of diferent fitting methods, notably based on Lorentzian and Voigt functions. We suggest that the most suitable approach to fitting pure Fh at liquid helium temperature is with two sextets (A and B) fitted using an extended Voigt-based function with the ability to apply probability distributions to each hyperfine parameter. 2-line Fh: A (δ = 0.49 mm/s; ε = 0.00 mm/s; Bhf = 50.1 T) and B (δ = 0.42 mm/s; ε = –0.01 mm/s; Bhf = 46.8 T) 6-line Fh: A (δ = 0.50 mm/s; ε = –0.03 mm/s; Bhf = 50.2 T) and B (δ = 0.40 mm/s; ε = –0.05 mm/s; Bhf = 47.1 T). We interpret the two sextets to be due to either diferences in the coordination environment of iron, i.e., in tetrahedral or octahedral sites, the presence of a disordered surface phase, or a combination of both. We hope that provoking a discussion on the use of MBS for Fh will help develop a greater understanding of this mineral, and other short-range ordered iron minerals, which are so important in environmental processes. [ABSTRACT FROM AUTHOR]

Iron(II) oxide, wüstite, is the iron oxide with the lowest oxygen content. Under ambient conditions it is metastable for two reasons: (1) it undergoes eutectoid decomposition to Fe and Fe3O4 below ≈570° C, and (2) depending on temperature, it is thermodynamically stable only for very low oxygen partial pressures, down to below 10−20 bar. Hence, for the growth of single crystals from the melt, the growth atmosphere must contain reducing components to keep the oxygen partial pressure on the required low level. With Ar/CO2/CO mixtures this aim can be reached. It is shown experimentally and by thermodynamic calculation, that the grown crystals contain carbon inclusions. Theoretically it is shown that wüstite crystals without carbon inclusions could be grown in humid N2/H2 mixtures. First experiments are presented in this article, but a further adjustment of experimental parameters is required. [ABSTRACT FROM AUTHOR]