Local Structure in Orthorhombie and Tetragonal Ba2YCu3O7-y: The Role of Oxygen Vacancies for High Tc Superconductivity

Abstract

Cu valency and local structure in the orthorhombic and tetragonal phases of high T _c superconductor Ba₂YCu₃O_7-y (0.03<yz = 1/2 plane modify both Cu valency and local structure. The near-edge spectra show that Cu ions at Cu₁ sites in tetragonal Ba₂YCu₃O_7-y are monovalent. From the temperature dependence of the Cu-O distance and its mean relative displacement, it is suggested that the breathing mode Cu-O stretching vibration is slightly suppressed in the tetragonal phase, which may degrade superconducting properties.