Nuclear Quadrupole Resonance Study of Copper in Electron-Irradiated YBa2Cu3O6.95

NQR of Cu in YBa2Cu3O6.95 was investigated before and after low-temperature electron irradiation as well as after annealing at several distinct temperatures up to 440 K. Irradiation with 2.76 MeV electrons (fluence ϕt = 2.2 · 1023 e-/m 2) decreased the critical temperature Tc from 91.8 K to 89.5 K. The NQR spectra indicate that the e- irradiation displaces so-called 0 (4) atoms in the Cu - O chains. It is argued that this results in a modification of the average valence of the Cu(2) atoms in the planes, which explains the reduction of Tc. Recovery of the radiation damage sets in (presumably due to the onset of mobility of displaced oxygen atoms) during annealing at 300 K but was still incomplete at 440 K.