MEM Analysis on Electron Density Distribution of Superconductors, Pb₂Sr₂Y_0.90Sr_0.10Cu₃O₈, Pb₂Sr₂Y_1−xCa_xCu₃O₈ (x=0.25 and 0.41) and Pb₂Sr₂Ho_0.64Ca_0.36Cu₃O₈

Abstract

Detailed crystal structures of high-T_c superconductors Pb₂Sr₂Y_0.90Sr_0.10Cu₃O₈, Pb₂Sr₂Y_1−xCa_xCu₃O₈ (x=0.25 and 0.41) and Pb₂Sr₂Ho_0.64Ca_0.36Cu₃O₈ were successfully determined by means of single crystal X-ray diffraction at room temperature. Space symmetry changes from C2/m (x=0.10 and 0.25) to Cmmm (x=0.36 and 0.41) with increasing divalent cation concentration, x. Their electron density distributions are determined by means of the maximum entropy method (MEM). Two- or four-splitting oxygen peaks clearly appear in the electron density maps of PbO plane, which is consistent with oxygen disorder models introduced to the present structure determination. In the electron density maps of monovalent copper plane, no peak corresponding to excess oxygens was observed at the 1×10³ e/nm³ contour level. In the vicinities of divalent copper in the conducting plane, some anomalous electron density distribution is represented in the yttrium compounds.