Estimation of Cage Structures for Silicon Clatherate Compound Ba₈Ni₆Si₄₀ by HRTEM Imaging and Computer Simulation

抄録

Recently, the new finding that silicon clathrates containing Ba and/or Na, (Ba,Na)_xSi₄₆ , show high superconductivity with a transition temperature (Tc) has enhanced interest in related materials. A Ni and Ba containing ternary silicon clathrate compound, Ba₈Ni₆Si₄₀, was synthesized by simple melting of the constituent elements, and its crystal structure was studied by means of high resolution transmission electron microscopy (HRTEM). Clear structural images could be observed along the [100] and [111] directions; only these directions had the arrangement of 12- and 14- polyhedron cages in a row. The images were closely related to an empty space in each cage. The observed HRTEM images agreed well with the calculated images based on the structural model obtained by the X-ray Rietveld refinement method. In this paper, the cage structures of Ba₈Ni₆Si₄₀ will be clearly estimated by HRTEM imaging and coumputer simulation.