tent of added vanadium atoms. When the number of V The structure of the ternary oxide 6 Bi 2 O 3 -V 2 O 5 has been atoms increases from 9 : 1, it is no longer possible to retain investigated using single crystal X-ray diffraction data. It has the type I structure, and some of the Bi atoms between a fluorite-type superstructure with a pseudo monoclinic cell, the vanadium layers will be replaced by V atoms. In recent a ؍ 20.023 A ˚, b ؍ 11.668 A ˚, c ؍ 20.472 A ˚, and  ؍ 107.13؇, electron diffraction studies, Zhou reported that the 6 : 1 (the relation to the fluorite subcell is a ȃ 3/2[1, 1, 2] c , b ȃ compounds have structure types designated as types IIa-3/2[1, 1, 0] c , and c ȃ 1/2[5, 5, 2] c ), but the real crystal symmetry IIc (5, 7). He has proposed a model structure which is is P1. The positions of metal atoms are refined to R ؍ 0.12. composed of V 4 O 10 tetrahedral clusters. However, details The structure is characterized by six cation layers along the c of the structure are not given yet. The aim of the present axis, each containing 18 metal atoms. The cation arrangement study is to determine this structure. Single crystal samples can be represented using the numbers of V atoms as 4-0-4-4were grown with the composition of 6 : 1, and X-ray diffrac-0-4. Along the b axis, the crystal has square wave type displacetion data were collected at room temperature using a fourments (ȃ0.6 A ˚). The origin of this large distortion is attributed to the Coulomb repulsion between V atoms in the nearest neighcircle diffractometer.