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Actual Structure

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Alessandro Guastoni – One of the best experts on this subject based on the ideXlab platform.

  • what is the Actual Structure of samarskite y a tem investigation of metamict samarskite from the garnet codera dike pegmatite central italian alps
    American Mineralogist, 2016
    Co-Authors: Giancarlo Capitani, Enrico Mugnaioli, Alessandro Guastoni
    Abstract:

    We investigated, by scanning and transmission electron microscopy (SEM, TEM), wavelength- and energy-dispersive spectroscopy (WDS, EDS), and electron diffraction tomography (EDT), several (Y-REE-U-Th)-(Nb-Ta-Ti) oxides from the Garnet Codera dike pegmatite (Central Italian Alps). These oxides have compositions in the samarskite-(Y) field and yield an amorphous response from the single-crystal X-ray diffractometer. Backscattered electron images reveal that the samples are zoned with major substitutions involving (U+Th) with respect to (Y+REE). At the TEM scale, the samples show a continuous range of variability both in terms of composition and in radiation damage, and the amount of radiation damage is directly correlated with the U-content. Areas with high U-content and highly damaged show crystalline, randomly oriented nanoparticles that are interpreted as decomposition products of the metamictization process. On the other hand, areas with lower U-content and radiation dose contained within 0.7×10 16 α-event/mg, although severely damaged, still preserve single-crystal appearance. Such areas, noticeably consisting of relicts of the original samarskite Structure, were deeply investigated by electron diffraction techniques. Surprisingly, the retrieved crystal Structure of untreated samarskite is consistent with aeschynite and not with ixiolite (or columbite), as believed so far after X-ray diffraction experiments on annealed samples. In particular, the resolved Structure is a niobioaeschynite-(Y), with Pnma space group, cell parameters a = 10.804(1), b = 7.680(1), c = 5.103(1) A, and composition (Y 0.53 Fe 0.22 Ca 0.10 U 0.09 Mn 0.07 ) Σ=1 (Nb 1.07 Ti 0.47 Fe 0.34 Ta 0.07 W 0.06 ) Σ=2 O 6 . If this finding can be confirmed and extended to the other members of the group [namely samarskite-(Yb), calciosamarskite, and ishikawaite], then the samarskite mineral group should be considered no longer as an independent mineral group but as part of the aeschynite group of minerals. It is finally suggested that the rare crystalline sub-micrometric ixiolite domains, occasionally spotted in the sample by TEM, or the nanoparticles detected in highly metamict areas interpreted as decomposition product of the metamictization process, which may have in fact the ixiolite Structure, act as seeds during annealing, leading to the detection of ixiolite peaks in the X-ray powder diffractograms.

Yves Jean – One of the best experts on this subject based on the ideXlab platform.

  • Ab initio study of the coordination modes of tetrahydroborato ligands: what is the Actual Structure of the tris(tetrahydroborato)bis(trimethylphosphine) titanium complex
    Inorganic Chemistry, 1993
    Co-Authors: François Volatron, Miquel Duran, Agustí Lledós, Yves Jean
    Abstract:

    The Structure of the d 1 complex Ti(BH 4 ) 3 (PH 3 ) 2 is studied by means of ab initio UHF calculations including correlation energy at the MP2 level. This complex is used as a model for the Ti(BH 4 ) 3 (PMe 3 ) 2 complex characterized by Girolami et al. Sixteen Structures which differ by the borohydride coordination modes are optimized through an analytical gradient method. The energetical ordering of these Structures is analyzed through an electron count. We find that the optimal Structure corresponds to a η 2 ,η 2 ,η 3 coordination mode, a result in disagreement with the experimental data, which have been interpreted in terms of η 1 ,η 1 ,η 2 coordination

Yasushige Kuroda – One of the best experts on this subject based on the ideXlab platform.

  • Actual Structure of dissolved zinc ion restricted in less than 1 nanometer micropores of carbon
    The Journal of Physical Chemistry C, 2011
    Co-Authors: Takahiro Ohkubo, Masayasu Nishi, Yasushige Kuroda
    Abstract:

    The Structures and properties of hydrated ions confined in solid nanospaces are not substantially understood, although they are indispensable for the development of new devices such as electrical d…