Oxygen Nonstoichiometry and Chemical Diffusion Coefficient of Oxygen in Ba2YCu3O7−x

Abstract

The oxygen nonstoichiometry x and the chemical diffusion coefficient of oxygen in Ba2YCu3O7−x were measured by means of thermogravimetry as a function of oxygen partial pressure and temperature over the ranges 102 <Po2/Pa<105and 698<T/K<1173. The oxygen partial pressure dependence of x in Ba2Cu3O7−x obtained in this study was in good agreement with those previously reported by other researchers. The chemical diffusion coefficients of oxygen in Ba2YCu3O7−x with various oxygen nonstoichiometry x=0.063–0.77 were measured, and they increased with decreasing oxygen nonstoichiometry x at constant temperature. The compositional dependence of the chemical diffusion coefficient changed at about x=0.35, indicating the occurrence of the phase transition from the tetragonal to the orthorhombic structure. The activation energies of the chemical diffusion coefficients of oxygen in Ba2YCu3O7−x with various x were observed to be about 115·kJ mol−1, irrespective of oxygen nonstochiometry x. The self-diffusion coefficient of oxygen and the diffusion coefficient of oxygen vacancy were calculated from the chemical diffusion coefficient, and were compared with those of another superconductor La2−ySryCuO4−x.