Modulated structures of (Bi1−xPbx)2Sr2CoOy examined by high-resolution transmission electron microscopy

Abstract

Abstract The Pb-doped Bi-Sr-Co-O complex oxides, (Bi 1- x Pb x ) 2 Sr 2 CoO y with x =0.0 to 0.5, are examined by means of electron diffraction and high-resolution transmission electron microscopy (HRTEM) in order to clarify the effects of Pb-doping on the commensurate modulated structure of Bi 2 Sr 2 CoO y . Specimens with Pb content up to 10% ( x ≤0.1) have a commensurate modulated structure with modulation periodicity b s =4 b . At 15% substitution ( x =0.15), a stepwise increase of the value of b s is observed and the specimens with Pb content from 20 to 30% (0.2≤ x ≤0.3) have incommensurate modulations with b s ≈4.5 b . Modulated structures are absent for specimens with Pb more than 40% (0.4≤ x ). All of the modulated structures have body-centered orthorhombic symmetries (Mode I) and no transition to base-centered symmetry (Mode II) is observed even by high Pb-substitution in the present (Bi 1- x Pb x ) 2 Sr 2 CoO y system, although transition to Mode II is generally observed for superconducting Pb-doped Bi-Sr-Cu-O systems.