Growth and characterization of hollandite-type single crystal

Department of Pure and Applied Chemistry, Tokyo University of Science
â—‹Kenjiro Fujimoto Kenji Takamori Shigeru Ito

Hollandite-type compounds are represented by a general chemical formula AxMyN8-yO16 (x<2, y<2); where usually A = alkali or alkaline earth ions, M = di- or trivalent cations, and N = tetravalent cations. The structure has a tetragonal symmetry and contains tunnels extended along the unique axis with about 0.3 nm in period. This type of framework structure consists of double chains of (M,N)O6. octahedra edge-shared with adjacent ones. In the K-M-Ti-O hollandite-type compounds (M: Al, Ga etc.), these compounds have been studied as a one-dimensional fast ion conductor of alkali ions [1] and nuclear waste immobilizers [2,3] so far. In this study, K-(Fe or Ga)-Sn-O hollandite-type single crystals were grown in order to obtain crystallographic information and physical property by flux method. A mixture of (K2O)x(MoO3)y(B2O3)z system was used for flux composition. Needle like single crystal aggregate, about 3mm long and 60μm thickness, were collected by cooling down from 1623K to 1273K at 1.5-2.0K/hr.

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