Structures of Superconducting Ba sub 2 YCu sub 3 O sub (7-delta) and Semiconducting Ba sub 2 YCu sub 3 O sub 6 Between 25C and 750C

The structure and copper valence states of the 100K superconductor, Ba sub 2 YCu sub 3 O sub 7 have recently been determined by neutron powder diffraction between 5K and 300K[1], and at room temperature[2]. This 'oxygen deficient orthorhombic perovskite structure', now independently confirmed[3,4], is well ordered and stochiometric, and contains one Cu sup (+++) and two Cu sup (++) atoms distributed over two square planar oxygen co-ordinated sites. In the a-b plane CuO sub 4 squares are linked by their oxygen corners to form infinite sheets, while along the b-axis CuO sub 4 squares form infinite chains on the second Cu-site.