Oxygen diffusion in the superconducting oxide YBa2Cu3O7−x

Abstract

A low-frequency internal friction peak was observed at 200 °C for sintered YBa2Cu3O7−x bar specimens annealed at different temperatures between 400 and 650 °C. This peak is interpreted in terms of diffusional jumps of oxygen atoms in the basal planes between sublattice sites OA((1/2, 0,0) and OB(0,(1/2,0). These two sites are not crystallographically equivalent in orthorhombic symmetry. Oxygen diffusivity for planar diffusion in the basal planes was derived on the basis of a one-dimensional random-walk process, which yields: D=((1/4)d2CB/(CA+CB)ν ν0 exp(-HB/kT) =D0exp(-HB/kT), where HB=HA+ΔE. The parameters CA, CB, ν0, and HA are evaluated from internal friction data for the specimens of known oxygen deficiency x and ΔE, the poten- tial energy difference between sites OA and OB, from Boltzmann’s distribution law CA/CB=exp(-ΔE/kT). The preexponential factor D0=3.5×10−4 cm2/sec and the activation energy of the 200 °C internal-friction peak HA=1.03 eV are both temperature insensitive. By contrast, ΔE is temperature dependent; it is 0.23 eV at 400 °C and decreases as the temperature is raised, vanishing at 670 °C, the temperature of the orthorhombic-to-tetragonal transition temperature at which OA and OB sites become indistinguishable. Non-Arrhenius behavior exists between the oxygen diffusivity and the diffusion temperature in this type of diffusion mechanism.

Source-reported materials — not catalogue approval

Similar papers