Structural Changes as a Function of Oxygen Stoichiometry

All the structural determinations quoted in the previous sections were made on samples of Ba2YCu3Ox with composition 6.8 x 7.0. As shown in Table 1, for x = 7.0 all sites 0(4) are filled. When x 7.0 there must be oxygen vacancies in the structure and it was realized very soon that these are confined to the sites 0(4) in the chains parallel to the b-axis (13). The presence of vacancies on the 0(2) sites, reported by Beno et al. (10), and indicated in Table l,has not been confirmed in any other diffraction experiment and will not be considered further in the present discussion. 

TABLE 2. Atom Positions, Occupancies and Agreement Indices for Ba2YCus06. 

One of the most important aspects of the structure of Ba2Y Cu3Ox is the local arrangement of the oxygen atoms on the basal plane 

The existence of intermediate structures with various schemes of short-range oxygen ordering on the basal plane, indicates that the 

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