title: Direct observation of cesium at the interlayer region in phlogopite mica.
abstract: To investigate the sorption mechanism of cesium (Cs) into clay minerals, high-resolution (scanning) transmission electron microscopy (TEM/STEM) imaging of Cs in mica (phlogopite) has been conducted. Platy phlogopite powders were immersed in a cesium chloride (CsCl) solution to achieve Cs(+)-K(+) ion-exchange at the interlayer regions in phlogopite. To observe many phlogopite particles with the incident electron beam parallel to the mica layers, cross-sectional thin specimens were prepared from sedimented particles using a focused ion beam. High-angle annular dark-field imaging with STEM is superior to conventional high-resolution TEM (HRTEM) for visualizing Cs at interlayer sites even in thicker crystal regions and/or at lower magnification due to the intense Z-contrast of Cs. However, HRTEM is also practical for estimating the concentration of Cs at the interlayer site from the thickness dependence of the contrast at the interlayer region. Cs sorption of micas was previously thought to be localized mainly at the frayed-edge sites of mica crystals. However, the present observations indicate that Cs substitution of K occurs not around crystal edges but deep inside the crystals along specific interlayer regions.
authors.affiliation: Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Taiga
authors.initials: T
authors.lastname: Okumura
authors.forename: Kenji
authors.initials: K
authors.lastname: Tamura
authors.forename: Eiko
authors.initials: E
authors.lastname: Fujii
authors.forename: Hirohisa
authors.initials: H
authors.lastname: Yamada
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kogure
keywords: cesium; clay minerals; high-angle annular dark-field-scanning transmission electron microscopy; high-resolution transmission electron microscopy; mica; radioactive contamination