earticle

영어

The effects of electron beam (EB) irradiation on the superconducting critical temperature (Tc) and critical current density (Jc) of YBCO films were studied. The YBCO thin films were irradiated using a KAERI EB accelerator with an energy of 0.2 MeV and a dose of 1015–1016 e/cm2. A small Tc decrease and a broad superconducting transition were observed as the EB dose increased. The value of Jcs (at 20 K, 50 K and 70 K) increased at doses of 7.5×1015 and 2.2×1016 e/cm2. However, Jcs decreased as the dose increased further. The X-ray diffraction (XRD) analysis showed that the c axis of YBCO was elongated and the full width at half maximum (FWHM) increased as the dose increased, which is strong evidence of the atomic displacement by EB irradiation. The transmission electron microscopy (TEM) showed that the amorphous layer formed in the vicinity of the surfaces of the irradiated films. The amorphous phase was often present as an isolated form in the interior of the films. In addition to the formation of the amorphous phase, many striations running along the a-b direction of YBCO were observed. The high magnification lattice image showed that the striations were stacking faults. The enhancement of Jc by EB irradiation is likely to be due to the lattice distortion and the formation of defects such as vacancies and stacking faults. The decrease in Jc at a high EB dose is attributed to the extension of the amorphous region of a non-superconducting phase.