ELECTRON-MICROSCOPY, NEUTRON-DIFFRACTION, AND PHYSICAL-PROPERTIES OF BI4SR8CU5O19+Y

The preparation and study of the structural and physical properties of the so-called tubular-phase Bi4Sr8Cu5O19+y by neutron powder diffraction, high-resolution electron microscopy, electrical resistivity, and magnetic susceptibility measurements are reported. This oxide is closely related structurally to the n = 1 bismuth cuprate superconductor Bi2Sr2CuO6+y, differing by the presence of extra Sr-Cu-Sr perovskite layers perpendicular to the [CuO2] planes. Neutron powder diffraction results are essentially in agreement with previous structural refinements based on single-crystal X-ray diffraction data. The structur is described in the space group Fmmm with the oxygen atoms in the bismuth planes appearing disordered at intermediate positions between NaCl and bridging sites as occurs for superconductors in the family Bi2Sr2Can-1Cu(n)O2n+4. Electron diffraction patterns and HREM images show that such disorder does not lead to the existence of a structural modulation as in the above family: The extra Sr-Cu-Sr perovskite layers perpendicular to the [CuO2] planes convert the layered Bi2Sr2CuO6+y structure into a rigid network, preventing the corrugation of the slabs and the modulation of the structure. Calculations based on Brown's method show a heterogeneous charge distribution among copper ions. Study of powder neutron diffraction patterns between 1.5 and 998 K does not show either any relevant structural change nor evidence of 3D antiferromagnetic ordering. Electrical resistivity measurements in the 60 K less-than-or-equal-to T less-than-or-equal-to 300 K temperature range indicate semiconducting behavior. The observed magnetic susceptibility is consistent with the existence of paramagnetic defects within a 2D strongly correlated antiferromagnetism.