Crystal Structure and Tc of YBa2Cu3Oy (y>7)

Abstract
At a high oxygen pressure of 6 GPa, YBa2Cu3O y was heat-treated. With an increasing supply of oxygen, the crystal structure of the processed specimens gradually changed from orthorhombic (y=7) to tetragonal (y=7.7), whereas the onset of superconducting transition temperature consistently remained at 92 K for all of the specimens. The distribution of charges among the copper-oxygen chains and the CuO2 sheets in YBa2Cu3O y (y>7) are discussed.