Time evolved defects in proton-irradiated single-crystal YBa 2Cu 3O 7−δ

Abstract

Defects due to 200 MeV proton irradiation of single-crystal YBa 2Cu 3O 7−δ at fluxes from 10 14 to 10 16 protons/cm 2 have been examined with transmission electron microscopy (TEM) using both diffraction contrast and lattice imaging. TEM foils were prepared from single-crystals and characterized prior to irradiation for intrinsic defects. The TEM foils were irradiated at 200 MeV with the beam parallel to the c-axis. Defects with anisotropic strain contrast were not observed in foils examined within days of irradiation for fluences up to 10 15 p/cm 2. After aging for over 90 days, the same samples which originally showed no defects consistent with irradiation damage, showed defects with anisotropic strain contrast. Lattice imaging showed two types of defects, small clusters (∼0.5 nm) with no special orientation and extended defects 2 to 7 nm in length and 0.2 nm thick which concentrate along the {100} 〈010〉. The lattice image, TRIM calculations and DC magnetization data are consistent with these extended defects being CuO extrinsic stacking faults. These data imply that protons produce predominantly point defects of Cu and O which cluster over time.