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1. Structure and Oxidation States of Giant Unit Cell Compound Dy 117+x Fe 57–y Sn 112–z

   https://doi.org/10.1002/zaac.201700321  

   Brown, Alexander T. ; Barron, Keaton G. ; Salazar, Bryan G. ; Kirby, Parker ; McCandless, Gregory T. ; Walker, Amy V. ; Chan, Julia Y. ( November 2017 , Zeitschrift für anorganische und allgemeine Chemie)

   Motivated by the complex structure and properties of giant unit cell intermetallic compounds, a new isostructural Fe analogue of the Dy₁₁₇Co₅₇Sn₁₁₂structure type was synthesized. Single crystals of Dy₁₂₂Fe₅₅Sn₁₀₁were grown at 1260 °C via a Dy–Fe eutectoid flux. The Fe analogue also adopts the space groupFm3mwith lattice parametersa= 29.914(9) Å,V= 26769(23) ų, andZ= 4. Dy₁₂₂Fe₅₅Sn₁₀₁has a large cell volume, structural complexity, and consists of seven Dy, eight Fe, and ten Sn unique crystallographic sites. There are fifteen fully occupied atomic positions, three unique pairs of alternating atomic positions with positional disorder, and seven partially occupied atomic sites. Within this complex unit cell, only approximately half the unique atomic positions are fully occupied with the remainder of the atoms either positionally or occupationally disordered. X‐ray photoelectron spectroscopy indicates that the compound contains Dy³⁺, Fe⁰, Fe²⁺, Sn⁰, and Sn⁴⁺.

    

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2. The first samples from Almahata Sitta showing contacts between ureilitic and chondritic lithologies: Implications for the structure and composition of asteroid 2008 TC 3

   https://doi.org/10.1111/maps.13390  

   Goodrich, Cyrena Anne ; Zolensky, Michael E. ; Fioretti, Anna Maria ; Shaddad, Muawia H. ; Downes, Hilary ; Hiroi, Takahiro ; Kohl, Issaku ; Young, Edward D. ; Kita, Noriko T. ; Hamilton, Victoria E. ; et al ( October 2019 , Meteoritics & Planetary Science)

   Almahata Sitta (AhS), an anomalous polymict ureilite, is the first meteorite observed to originate from a spectrally classified asteroid (2008TC₃). However, correlating properties of the meteorite with those of the asteroid is not straightforward because the AhS stones are diverse types. Of those studied prior to this work, 70–80% are ureilites (achondrites) and 20–30% are various types of chondrites. Asteroid 2008TC₃was a heterogeneous breccia that disintegrated in the atmosphere, with its clasts landing on Earth as individual stones and most of its mass lost. We describe AhS 91A and AhS 671, which are the first AhS stones to show contacts between ureilitic and chondritic materials and provide direct information about the structure and composition of asteroid 2008TC₃. AhS 91A and AhS 671 are friable breccias, consisting of a C1 lithology that encloses rounded to angular clasts (<10 μm to 3 mm) of olivine, pyroxenes, plagioclase, graphite, and metal‐sulfide, as well as chondrules (~130–600 μm) and chondrule fragments. The C1 material consists of fine‐grained phyllosilicates (serpentine and saponite) and amorphous material, magnetite, breunnerite, dolomite, fayalitic olivine (Fo 28‐42), an unidentified Ca‐rich silicate phase, Fe,Ni sulfides, and minor Ca‐phosphate and ilmenite. It has similarities toCI1 but shows evidence of heterogeneous thermal metamorphism. Its bulk oxygen isotope composition (δ¹⁸O = 13.53‰, δ¹⁷O = 8.93‰) is unlike that of any known chondrite, but similar to compositions of severalCC‐like clasts in typical polymict ureilites. Its Cr isotope composition is unlike that of any known meteorite. The enclosed clasts and chondrules do not belong to the C1 lithology. The olivine (Fo 75‐88), pyroxenes (pigeonite of Wo ~10 and orthopyroxene of Wo ~4.6), plagioclase, graphite, and some metal‐sulfide are ureilitic, based on mineral compositions, textures, and oxygen isotope compositions, and represent at least six distinct ureilitic lithologies. The chondrules are probably derived from type 3OCand/orCC, based on mineral and oxygen isotope compositions. Some of the metal‐sulfide clasts are derived fromEC. AhS 91A and AhS 671 are plausible representatives of the bulk of the asteroid that was lost. Reflectance spectra of AhS 91A are dark (reflectance ~0.04–0.05) and relatively featureless inVNIR, and have an ~2.7 μm absorption band due toOH⁻in phyllosilicates. Spectral modeling, using mixtures of laboratoryVNIRreflectance spectra of AhS stones to fit the F‐type spectrum of the asteroid, suggests that 2008TC₃consisted mainly of ureilitic and AhS 91A‐like materials, with as much as 40–70% of the latter, and <10% ofOC,EC, and other meteorite types. The bulk density of AhS 91A (2.35 ± 0.05 g cm⁻³) is lower than bulk densities of other AhS stones, and closer to estimates for the asteroid (~1.7–2.2 g cm⁻³). Its porosity (36%) is near the low end of estimates for the asteroid (33–50%), suggesting significant macroporosity. The textures of AhS 91A and AhS 671 (finely comminuted clasts of disparate materials intimately mixed) support formation of 2008TC₃in a regolith environment. AhS 91A and AhS 671 could represent a volume of regolith formed when aCC‐like body impacted into already well‐gardened ureilitic + impactor‐derived debris. AhS 91A bulk samples do not show a solar wind component, so they represent subsurface layers. AhS 91A has a lower cosmic ray exposure (CRE) age (~5–9 Ma) than previously studied AhS stones (11–22 Ma). The spread inCREages argues for irradiation in a regolith environment. AhS 91A and AhS 671 show that ureilitic asteroids could have detectable ~2.7 μm absorption bands.

    

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3. Synthesis, Elasticity, and Spin State of an Intermediate MgSiO 3 ‐FeAlO 3 Bridgmanite: Implications for Iron in Earth's Lower Mantle

   https://doi.org/10.1029/2020JB019964  

   Zhu, Feng ; Liu, Jiachao ; Lai, Xiaojing ; Xiao, Yuming ; Prakapenka, Vitali ; Bi, Wenli ; Alp, E. Ercan ; Dera, Przemyslaw ; Chen, Bin ; Li, Jie ( July 2020 , Journal of Geophysical Research: Solid Earth)

   Fe‐Al‐bearing bridgmanite may be the dominant host for ferric iron in Earth's lower mantle. Here we report the synthesis of (Mg_0.5Fe³⁺_0.5)(Al_0.5Si_0.5)O₃bridgmanite (FA50) with the highest Fe³⁺‐Al³⁺coupled substitution known to date. X‐ray diffraction measurements showed that at ambient conditions, the FA50 adopted the LiNbO₃structure. Upon compression at room temperature to 18 GPa, it transformed back into the bridgmanite structure, which remained stable up to 102 GPa and 2,600 K. Fitting Birch‐Murnaghan equation of state of FA50 bridgmanite yieldsV₀ = 172.1(4) ų,K₀ = 229(4) GPa withK₀′ = 4(fixed). The calculated bulk sound velocity of the FA50 bridgmanite is ~7.7% lower than MgSiO₃bridgmanite, mainly because the presence of ferric iron increases the unit‐cell mass by 15.5%. This difference likely represents the upper limit of sound velocity anomaly introduced by Fe³⁺‐Al³⁺substitution. X‐ray emission and synchrotron Mössbauer spectroscopy measurements showed that after laser annealing, ~6% of Fe³⁺cations exchanged with Al³⁺and underwent the high‐ to low‐spin transition at 59 GPa. The low‐spin proportion of Fe³⁺increased gradually with pressure and reached 17–31% at 80 GPa. Since the cation exchange and spin transition in this Fe³⁺‐Al³⁺‐enriched bridgmanite do not cause resolvable unit‐cell volume reduction, and the increase of low‐spin Fe³⁺fraction with pressure occurs gradually, the spin transition would not produce a distinct seismic signature in the lower mantle. However, it may influence iron partitioning and isotopic fractionation, thus introducing chemical heterogeneity in the lower mantle.

    

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4. A Novel Self‐Assembled Cobalt‐Free Perovskite Composite Cathode with Triple‐Conduction for Intermediate Proton‐Conducting Solid Oxide Fuel Cells

   https://doi.org/10.1002/adfm.202209695  

   Tong, Hua ; Fu, Min ; Yang, Yang ; Chen, Fanglin ; Tao, Zetian ( September 2022 , Advanced Functional Materials)

   A traditional composite cathode for proton‐conducting solid oxide fuel cells (H‐SOFCs) is typically obtained by mixing cathode materials and proton conducting electrolyte of BaCe_0.7Y_0.2Zr_0.1O_3–δ(BZCY), providing chemical and thermal compatibility with the electrolyte. Here, a series of triple‐conducing and cobalt‐free iron‐based perovskites as cathodes for H‐SOFCs is reported. Specifically, BaCe_xFe_1–xO_3–δ(x = 0.36, 0.43, and 0.50) shows various contents of two single phase perovskites with an in situ heterojunction structure as well as triple conductivity by tailoring the Ce/Fe ratios. The cell performance with the optimized BaCe_0.36Fe_0.64O_3–δ(BCF36) cathode composition reaches 1056 mW cm⁻²at 700 °C. Moreover, a record cell performance of 1525 mW cm⁻²at 700 °C is obtained by modifying the BCF36 cathode microstructure through a spraying method, demonstrating high promise with Co‐free cathodes for H‐SOFCs.

    

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5. Beckettite, Ca 2 V 6 Al 6 O 20 , a new mineral in a Type A refractory inclusion from Allende and clues to processes in the early solar system

   https://doi.org/10.1111/maps.13771  

   Ma, Chi ; Krot, Alexander N. ; Paque, Julie ; Tschauner, Oliver ; Nagashima, Kazuhide ( December 2021 , Meteoritics & Planetary Science)

   Beckettite (Ca₂V₆Al₆O₂₀; IMA 2015‐001) is a newly discovered refractory mineral, occurring as micrometer‐sized grains intergrown with hibonite and perovskite, and surrounded by secondary grossular, anorthite, coulsonite, hercynite, and corundum. It occurs within highly altered areas in a V‐rich, Type A Ca‐Al‐rich inclusion (CAI), A‐WP1, from the Allende CV3 carbonaceous chondrite. The type beckettite has an empirical formula of (Ca_1.99Na_0.01)(V³⁺_3.47Al_1.40Ti⁴⁺_0.57Mg_0.25Sc_0.08Fe²⁺_0.04)(Al_5.72Si_0.28)O₂₀, with a triclinic structure in space groupPand cell parametersa= 10.367 Å,b= 10.756 Å,c= 8.895 Å, α = 106.0°, β = 96.0°, γ = 124.7°,V= 739.7 ų, andZ= 2, which leads to a calculated density of 3.67 g cm⁻³. Beckettite’s general formula is Ca₂(V,Al,Ti,Mg)₆Al₆O₂₀and the endmember formula is Ca₂V₆Al₆O₂₀. Beckettite is slightly¹⁶O‐depleted (Δ¹⁷O = −16 ± 2‰) compared to the coexisting hibonite and spinel −24 ± 2‰. Beckettite is a primary high‐temperature mineral resulting from igneous crystallization of an¹⁶O‐rich V‐rich CAI melt together with V‐bearing hibonite, perovskite, burnettite, spinel, and paqueite. Subsequently, beckettite experienced an incomplete isotope exchange with an¹⁶O‐poor aqueous fluid (Δ¹⁷O = −3 ± 2‰) on the Allende parent asteroid.

    

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