K. Nakashima

Bio: K. Nakashima is an academic researcher from University of Tokyo. The author has contributed to research in topics: Irradiation & Pulsed laser deposition. The author has an hindex of 1, co-authored 1 publications receiving 27 citations.

Effect of ion-irradiation and annealing on superconductive property of PLD prepared YBCO tapes

Abstract: PLD (pulsed laser deposition) prepared YBCO tapes were irradiated by 450 MeV Xe 23+ or 500 MeV Au 31+ ions with irradiation fluence from 1.0 × 10 10 to 1.0 × 10 12 ions/cm 2 to investigate for the effective condition which enhances J c . As a result of ion-irradiation, we observed the enhancement of J c especially at high applied magnetic field in 77 K. It was also shown that T c decreased with irradiation fluence. These changes of superconductive properties were found to depend on the kind of the ion and the energy. We also studied post-annealing effect on the irradiated tapes. After the ion-irradiation, the samples were annealed at the temperature of 473 K or 673 K in the oxygen atmosphere for 2 h and then quenched. From the post-annealing experiments, we concluded that the post-annealing was a good way to recover T c without decreasing J c .

Flux pinning by discontinuous columnar defects in 74 MeV Ag-irradiated YBa2Cu3O7 coated conductors

Abstract: Linear damage tracks are created in production-quality YBCO coated conductors by irradiation with 61–74 MeV Ag ions. The ion tracks are observed by transmission electron microscopy to be elongated but discontinuous. The in-field transport critical current ( I c ) is enhanced significantly for fields applied parallel to the irradiation direction with a broad peak appearing in the magnetic field-angle dependence of the critical current, coinciding with the irradiation direction. The zero-field I c is typically reduced somewhat, however annealing at 200 °C partially restores this and enhances the in-field I c even for field parallel to the irradiation direction. Lower energies tend to produce a weaker peak, but also retain the zero-field I c to a greater extent, consistent with a trend of greater discontinuity in the ion tracks.

Activation energy and excess conductivity analysis of (Ag)x/CuTl-1223 nano-superconductor composites

Abstract: Silver (Ag) nanoparticles were added into (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (CuTl-1223) high Tc superconducting matrix to get (Ag)x/CuTl-1223, x = 0, 0.5, 1.0, 2.0, and 4 wt. %, nano-superconductor composites. The activation energy {U (eV)} and zero resistivity critical temperature {Tc (0)} were increased with increasing contents of Ag nanoparticles in (CuTl-1223) phase up to x = 2.0 wt. %. The increase of activation energy is most probably due to interaction of carriers with the metallic Ag nanoparticles present at grain boundaries of the host CuTl-1223 superconducting matrix. The systematic increase in Tc (0) and gradual decrease in normal state resistivity {ρ300 K (Ω cm)} may be due to improved inter-grains coupling by filling up the voids and pores with the inclusion of metallic Ag nanoparticles at the grain-boundaries. There are two possible mechanisms associated with the inclusion of Ag nanoparticles, one is the formation of non-superconducting regions causing the increase of activation energy and other (d...