Gamma ray irradiation effects on electrical transport and microwave properties of BISCO superconducting films

High-T-c Superconducting films of Bi-Sr-Ca-Cu-O (2:2:1:2) have been synthes ized by spray pyrolysis of nitrate precursors onto yttria stabilized zircon ia (YSZ). gamma-ray irradiation of the sample, was carried out using a Co-6 0 source Of 10(3) Ci Strength for several hundreds of hours; the dose recei ved by the samples was 80 K rad/hr. Superconducting properties such as crit ical transition temperature (T-c), resistivity (KR), critical current densi ty (J(tc)). Voltage-time relaxation (Vt) and microwave induced de voltage w ere investigated as a function of temperature down to 77 K after gamma-ray irradiation. gamma-ray irradiation was found to have practically no effect on its structural modification and on the critical transition temperature. However, transport critical current density (J(tc)) increased. The increase of pinning energies with irradiation suggests that these changes in proper ties are dominated by radiation-induced randomly distributed mobile oxygen defects in the films. An appreciable decrease in the microwave-induced dc v oltage at 77 K was also observed after irradiation which suggests that the mobile defects are clustered at the major defect region and reduce the tota l number of weak links. These results suggests that oxygen defects induced by gamma-ray irradiation of BISCO films act as important and major pinning centers which is responsible for the enhancement of J(tc) and reduction of microwave induced dc voltage.