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

Hollandite-type compounds are represented by a general chemical formula A_xM_yN_8-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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[2] A. E. Ringwood, S. E. Kesson, N. G. Ware, W. Hibberson and A. Major, Nature 278, 219, (1979).
[3] H. Mitamura, S. Matsumoto, M. W. A. Stewart, T. Tsuboi, M. Hashimoto, E. R. Vance, K. P. Hart, Y. Togashi, H. Kanazawa, C. J. Ball and T. J. White, J. Am. Ceram. Soc. 77(9), 2255, (1994).