CRYSTAL-STRUCTURE OF BI2SR2CUO6 - A STRUCTURE BASED ON PERIODIC CRYSTALLOGRAPHIC SHEAR PLANES IN THE 2201-STRUCTURE

The crystal structure of the insulating phase Bi2Sr2CuO6 is reported. The refinements were performed on X-ray and neutron powder diffraction data. The R values were R(i) = 10.56% (R(p) = 6.67%, R(wp) = 8.40%) f or X-ray and R(i) = 7.47% (R(p) = 5.01%, R(wp) = 6.45%) for neutron da ta. The structure is derived from that of the pseudo-tetragonal ''2201 '' phase by a periodic crystallographic shear parallel to the c(tetr.) axis. Slabs of ''2201'' type with a thickness of eight octahedra are then formed which are parallel to (001). The beta angle of the monocli nic cell results from the periodic crystallographic shear which is a s imple translation along the c axis. This structural model has been con firmed by HRTEM where the slabs of ''2201'' have been observed.