OXYGEN KNOCK-OUT AND OTHER STUDIES IN ALPHA-IRRADIATED POLYCRYSTALLINE BI-2212 SUPERCONDUCTOR

Bulk polycrystalline samples of Bi2Sr2CaCu2O8+z (Bi-2212) have been ir radiated with 40 MeV alpha-particles. T-c increases up to a certain do se. The increase in T-c is correlated with the knock-out of oxygen, wh ich has been verified by the determination of the oxygen contents of t he irradiated samples by iodometry. A model of the knock-out of oxygen is proposed on the basis of Monte-Carlo TRIM calculations. Resistivit y versus temperature of the irradiated samples shows fairly metallic b ehaviour up to a certain dose. Excess conductivity analysis shows a cr oss-over from 2D to 3D behaviour in conductivity for the unirradiated sample. However, for irradiated samples, the critical fluctuation regi me sets in. The interlayer coupling strengths decrease with the increa se in the irradiation dose. The sample with the highest dose shows a n onmetallic behaviour is resistivity. A detailed analysis shows a condu ctivity behaviour in the nonmetallic region characteristic of three-di mensional variable range hopping of charge carries.