Abstract
The crystal structure of the high-Tc Bi2-x(Ca, Sr)3Cu2+xO9-y with x=0.2 and y=0.78 was studied by means of neutron and X-ray powder diffraction. Since the unit cell parameters were relatively large for powder diffraction analysis, an averaged structure was refined, assuming an orthorhombic sub-cell (a=5.39 Å, b=5.39 Å and c=30.37 Å) which corresponds to 1/5 of the unit cell: This is a derivative of Bi4Ti3O12. The double perovskite unit interleaved by the double bismuth layers is B-type, i.e. a CuO6 octahedron is surrounded by eight alkaline earth metal ions. The pyramidal CuO5 configuration is found in this oxide. The copper valency is estimated at about 2.3 on the basis of the determined chemical composition.