Modulated structure of the superconducting compounds Bi2Sr2Ca n-1Cu n O y withn=1 and 2

The incommensurate modulated structures of high-T _c superconducting phases Bi₂Sr₂Ca _n–1Cu _n O _y (n=1 and 2) have been studied using symmetry properties of four-dimensional super-spacegroups and electron diffraction as well as high resolution electron microscopy are used to describe the properties of the incommensurate modulated structure in the compounds. The main results are planar monoclinic symmetryP ^B _{2/b 11} orP B _{b 1} for Bi₂Sr₂CuO _y (n=1) and orthorhombic symmetryN ₁₁₁ ^Bbmb orN ₁₁₁ ^Bb2b for Bi₂Sr₂CaCu₂O _y (n=2). The temperature dependence of the modulated structure of Bi₂Sr₂CaCu₂O _y has been investigated from –190°C to 800°C. Some structure properties of Bi₂Sr₂Ca₂Cu₃O _y (n=3) are presented for comparison.