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Abstract: This work describes the application of microfocus X-ray absorption spectroscopy (XAS) and X-ray photo-emission electron microscopy (XPEEM) to the study of the complex mineralogical intergrowths within the Santa Catharina meteorite. The Santa Catharina meteorite of this study (BM52283 from the meteorite collection of the Natural History Museum, London, UK) primarily comprises a taenite bulk host phase (Fe:Ni ratio = 70.9 ± 0.8%:29.1 ± 0.8%) with a set of oxide-bearing cloudy zone textured regions (Fe:Ni:O ratio = 40.4 ± 0.3%:49.0 ± 0.7%:10.6 ± 0.8% at the core and Fe:Ni:O ratio = 34.4 ± 1.5%:42.7 ± 0.6%:22.9 ± 1.8% towards the rims) and numerous schreibersite (Fe:Ni:P ratio = 38.6 ± 1.6%:38.4 ± 0.9%:23.0 ± 0.5%) inclusions. Between the schreibersite and the taenite are rims up to 50 μm across of Ni-rich kamacite (Fe:Ni ratio = 93.4 ± 0.4%:6.6 ± 0.5%). No chemical zoning or spatial variations in the Fe and Ni speciation was observed within either the schreibersite or the kamacite phases. The oxide-bearing cloudy zone textured regions mostly comprise metallic Fe-Ni alloy, predominantly tetrataenite. Within the oxide phases, the Fe is predominantly, but not entirely, tetrahedrally co-ordinated Fe3+ and the Ni is octahedrally co-ordinated Ni2+. Structural analysis supports the suggestion that non-stoichiometric Fe2NiO4 trevorite is the oxide phase. The trevorite:tetrataenite ratio increases at the edges of the oxide-bearing cloudy zone textured regions indicating increased oxidation at the edges of these zones. The spatial resolution of the XPEEM achieved was between 110 and 150 nm, which precluded the study of either the previously reported ∼ 10 nm precipitates of tetrataenite within the bulk taenite or any antitaenite.

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Abstract: We present Ba L3-X-ray Absorption Fine Structure (XAFS) data from a suite of barium carbonates (witherite, alstonite, barytocalcite), hydroxides, sulfate(vi) (barite) and a Ba-bearing organic compound to explore whether Ba L3-XAFS could be used to fingerprint structural states in biominerals such as celestite, aragonite and calcite. Although there is a general similarity between all X-ray Absorption Near Edge Structure (XANES), subtle differences are observed in detail, which allow almost all phases to be distinguished. The XANES are considered as composites of four components, termed ‘A’ (5255 eV), ‘B’ (5258 eV), ‘C’ (5268 eV) and ‘D’ (5273 eV). ‘A’ is observed in barium hydroxides and most visible in the first derivatives of the XANES data. The minimum after the Ba L3 white line lies at 5257 eV for most materials but higher (5261 eV) for barium hydroxides due to the influence of the ‘A’ component. ‘B’ is present in aragonite-group minerals (witherite and alstonite) and may be a fingerprint of that structural state. ‘C’ and ‘D’ overlap and form a board hump at ∼ 5270 eV, but the relative proportions of ‘C’ and ‘D’ are variable between phases and are to some degree diagnostic. Refinement of Extended X-ray Absorption Fine Structure (EXAFS) allows estimates of first shell (Ba–O) bond distances in all materials, which are within 4% of average distances estimated from diffraction studies. Subsequent shells (Ba–S for barite; Ba–metal in witherite, alstonite and barytocalcite) can be resolved. The state of Ba:Ca order in alstonite and barytocalcite is successfully modelled and both are found to be fully ordered. The significant static disorder in Ba-bearing minerals is accommodated successfully by large Debye–Waller values in the refinements. Combinations of XANES and EXAFS allow all phases to be identified, with the exception that the two hydrated barium hydroxides cannot be distinguished from each other. The XANES of a celestite (SrSO4 containing ∼ 100 ppm Ba) is comparable to the barite spectra after only seven cycles (collected over < 5 h), showing that XANES can be resolved in samples with low Ba concentrations. However we were unable to analyse successfully an aragonitic Porites coral skeleton (containing ∼ 3–4 ppm Ba) using the current instrumentation due to the proximity in energy of Ca Kα secondary X-radiation to the Ba Lα energy and which overloaded the X-ray detector. The use of multilayer crystal detectors will be required to resolve the Ba Lα energy in calcium carbonate samples containing low Ba concentrations. Alternatively Ba EXAFS may be accessible through the Ba K edge.

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Abstract: The structure and the electrical and magnetic properties of Mn-implanted Si, which exhibits ferromagnetic ordering at room temperature, are studied. Single-crystal n- and p-type Si wafers with high and low electrical resistivities are implanted by manganese ions to a dose of 5 × 1016 cm?2. After implantation and subsequent vacuum annealing at 850°C, the implanted samples are examined by various methods. The Mn impurity that exhibits an electric activity and is incorporated into the Si lattice in interstitial sites is found to account for only a few percent of the total Mn content. The main part of Mn is fixed in Mn15Si26 nanoprecipitates in the Si matrix. The magnetization of implanted Si is found to be independent of the electrical resistivity and the conductivity type of silicon and the type of implanted impurity. The magnetization of implanted Si increases slightly upon short-term postimplantation annealing and disappears completely upon vacuum annealing at 1000°C for 5 h. The Mn impurity in Si is shown to have no significant magnetic moment at room temperature. These results indicate that the room temperature ferromagnetism in Mn-implanted Si is likely to be caused by implantation-induced defects in the silicon lattice rather than by a Mn impurity.

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Abstract: Unexplained tissue inflammation in metal-on-metal hip replacements is suspected to be caused by implant-derived nanoparticles. The aim of this study was to investigate the nature of the metal particles in tissue surrounding metal-on-metal (MOM) hips that has been extracted during revision. Mapping of tissue surrounding the failed MOM hips was performed using microfocus X-ray Fluorescence (XRF). This revealed mainly Cr which was localized to the cellular regions. There was co-localisation of Co, were present, to areas of high Cr abundance. XANES of the tissue and appropriate standards revealed that the most common species were Cr(III) and Co(II). EXAFS analysis of the tissue and various metal standards revealed that the most abundant implant-related species was Cr(III) phosphate. Different tissue preparation methods, including frozen sectioning, were examined but were found not to affect the distribution or speciation of the metals in the tissue.