Polytype and polymorph identification of finely divided aluminous dioctahedral mica individual crystals with SAED. Kinematical and dynamical electron diffraction |
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Authors: | Anne-Claire Gaillot Victor A Drits David R Veblen Bruno Lanson |
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Institution: | 1.Institut des Matériaux Jean Rouxel (IMN),Université de Nantes, CNRS,Nantes Cedex 3,France;2.Morton K. Blaustein Department of Earth and Planetary Sciences,Johns Hopkins University,Baltimore,USA;3.Geological Institute of Russian Academy of Sciences,Moscow,Russia;4.ISTerre, Maison des Géosciences,CNRS–University of Grenoble,Grenoble Cedex 9,France |
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Abstract: | This work investigates the potential of selected-area electron diffraction (SAED) for the polytype and polymorph identification
of finely divided K-bearing aluminous dioctahedral mica. Individual mica crystals may indeed differ by their layer-stacking
sequence and by the inner structure of their octahedral sheets (polytypic and polymorphic variants, respectively). This diversity
of natural mica is commonly considered to be responsible for their morphological variety. The present article thus analyzes
the intensity distribution between hk0 beams as a function of the crystal structure and thickness. The comparison of ED calculations with experimental diffraction
data shows that predicted dynamical effects are not observed for finely divided dioctahedral mica. The influence of different
structure defects on calculated intensities is analyzed, and their widespread occurrence in natural mica is hypothesized to
be responsible for the limitation of dynamical diffraction effects. SAED may thus be used to identify the structure of individual
dioctahedral mica crystals using the kinematical approximation to simulate and qualitatively interpret the observed intensities. |
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