Effect of oxygen defects on transport properties and T-c of YBa2Cu3O6+x: Displacement energy for plane and chain oxygen and implications for irradiation-induced resistivity and T-c suppression

The effect of electron irradiation with energy from 20 to 120 keV on the resistivity, Hall coefficient, and superconducting critical temperature T-c of YBa2Cu3O6+x thin films has been studied. The threshold energy of incident electrons for T-c suppression has been found, and the displacement energy for oxygen in CuO2 planes has been evaluated as 8.4 eV for irradiation along the c axis. The kinetics of production of the in-plane oxygen vacancies has been studied and found to be governed by athermal recombination of vacancy-interstitial pairs. The evaluated recombination volume constitutes about 21 unit cells. The increase in the T-linear resistivity slope and Hall coefficient at unchanged T-c was observed in irradiations with subthreshold incident energies and was ascribed to the effect of chain oxygen displacements. The upper limit on the displacement energy for chain oxygen has been estimated as 2.8 eV. In x=0.9 samples the T-c suppression by in-plane oxygen defects and increase in residual resistivity have been found to be, respectively, -280 K and 1.5 m Omega cm per defect in the unit cell. It is shown that T-c suppression by in-plane oxygen defects is a universal function of the transport impurity scattering rate and can be described qualitatively by pair-breaking theory for d-wave superconductors with nonmagnetic potential scatterers. Evaluation of scattering and Fair-breaking rates as well as the scattering cross section and potential is given. A comparison of the influence of in-plane oxygen defects on transport properties with that of other in-plane defects, such as Zn and Ni substitutions for Cu, is also made.