Neutron powder diffraction study of orthorhombic Ba sub 2 YCu sub 3 O sub (6.5).

A neutron powder diffraction study has been performed on orthorhombic Ba sub 2 YCu sub 3 O sub (6.5). The sample was prepared in a sealed quartz tube at 450C by equilibrating the oxygen stoichiometry between equal molar amounts of Ba Sub 2 YCu sub 3 O sub 7 and Ba sub 2 YCu sub 3 O sub 6. The structure is intermediate between the O sub 6 and O sub 7 compounds since 1/2 of the oxygens which link one-dimensional chains have been removed. No long range order of oxygen atoms could be detected, however, background modulation at low angles may be related to short range ordering.