SiO2 nanoparticles addition effect on microstructure and pinning properties in YBa2Cu3Oy

Higher intra-granular and inter-granular performances of YBCO superconductor with TiO2 nano-sized particles addition

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.

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

Effect of SiO2 nano-particles and nano-wires on microstructure and pinning properties of YBa2Cu3O7-d

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...

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

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 .

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

The magnetic field dependence of the transverse magnetoresistance Δρ/ ρ0 and the Hall coefficient RH was measured for the graphite films of various thickness ranging from around 20 to 110 nm at temperatures between 4.2 K and 300 K. High quality of the crystallinity of these graphite films prepared by cleaving could be confirmed from the observation of Shubnikov-de Haas oscillation in RH. The saturation tendency revealed in the resistivity ρ versus magnetic field B characteristics for graphite films thinner than about 50 nm in the strong magnetic field region at low temperature, while as for all graphite films in this study, ρ varied in proportion to Bn (n>1) in the strong magnetic field region at high temperature. According to the transport theory for the simple two carriermodel in the strong magnetic field region, this saturation tendency should be due to the differencebetween electron and hole densities. It may be caused by some change of energy band structure in thin films. Furthermore, at high temperature, ρ versus B characteristics, common to all these graphite films, may be explained by the equal number density ofelectrons and holes due to thermal excitation.

Magnetoresistance Effect of Thin Films Made of Single Graphite Crystals (特集 カーボンアロイ学の進展)

In the junction of a superconductor (S) and a normal conductor (N), the superconducting proximity effect arises, and the transition temperature (Tc) and critical field (Hc) of S/N bilayer usually lower from those in the superconductor itself ( T c s , H c s ) . However, in the niobium/graphite corresponding to S/N bilayers, it was found by the authors that the ratio T c ∗ / T c s showed a periodic characteristics with kish graphite (KG) film thickness (dKG) and the peak values of the ratio exceeded 1.00 where niobium (Nb) film thickness (dNb) was 40 nm. In this study, we studied experimentally the relation between T c ∗ and dKG under some conditions of dNb in order to investigate the superconductivity of niobium/graphite bilayers in detail. As in the case of previous study, thin KG films of various thickness ranging from 20 to 160 nm were prepared. For making a specimen, Nb was deposited on a KG film and a quartz glass substrate simultaneously. Nb film thickness prepared in this study were 27 nm, 40 nm and 47 nm. Each resistance of Nb and Nb/KG films was measured at the same time. As the result, it was found that the ratio T c ∗ / T c s vs. dKG showed a periodic characteristics at all dNb in this study, and it is indicated that the larger interference effect can be observed under certain condition of dNb and dKG.

Superconducting proximity effect in niobium/graphite complex systems

The change in pinning properties of YBa 2 Cu 3 O 7− x (Y-123) prepared by MPMG process due to fast neutron irradiation and thermal annealing treatment was investigated in order to confirm that fast neutron irradiation is effective for the J c increase in practical material as well as single crystal. In this study, MPMG-processed Y-123 specimens (1.5 mm × 1.0 mm × 0.5 mm) with 0.5 wt% of Pt were irradiated with fast neutrons from 2.9 × 10 15  cm −2 to 8.0 × 10 18  cm −2 below 313 K. Before and after the fast neutron irradiation, J c was evaluated from the magnetic hysteresis loop at 20 K, 40 K and 60 K using the extended Bean’s model, and pinning potential was obtained from the magnetic relaxation curve at 20 K. In addition, T c was evaluated by AC magnetization measurement. The maximum values of J c were 1200 kA cm −2 at 20 K and 7 T, and 400 kA cm −2 at 40 K and 7 T. They exceeded the target value for its practical superconducting magnet uses e.g. nuclear fusion reactor, magnetic levitation, etc. Furthermore, T c was recovered sufficiently by the thermal annealing treatment. It turns out that the pinning centers introduced by neutron irradiation work effectively also in the practical material which has already included the strong pinning centers of dispersed Y-211 phase.

Jc increase of MPMG-processed YBa2Cu3O7−x (Y-123) bulk due to fast neutron irradiation

Effects of fast neutron irradiation and post-annealing on magnetic properties of Rb 3 C 60 were studied through the dc magnetization measurement. Rb 3 C 60 powder samples were prepared in an evacuated quartz glass tube, and the temperature and the magnetic field dependences of dc magnetization were measured before and after irradiation and after post-annealing. The neutron fluences were 1.0, 1.8 and 3.3 × 10 16  n/cm 2 , and the post-annealing was made at a temperature of 473 K for 3 h. Magnetic hysteresis of the samples irradiated at the fluence of 1.8 and 3.3 × 10 16  n/cm 2 disappeared, and the hysteresis curves hardly changed at the fluence of 1.0 × 10 16  n/cm 2 . As for the post-annealing effect, the hysteresis curves of the sample irradiated at the fluence of 1.8 × 10 16  n/cm 2 were completely recovered after annealing, while those of the other samples, which had a magnetic background before irradiation, were not recovered. In this study, it was found that the loss of superconductivity in Rb 3 C 60 powder is observed when the neutron irradiation fluence exceeds 1.0 × 10 16  n/cm 2 , and the lost superconductivity is completely recovered by the post-annealing at 473 K for 3 h.

Toshiharu Kubo

Papers

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

Magnetoresistance Effect of Thin Films Made of Single Graphite Crystals (特集カーボンアロイ学の進展)

Superconducting proximity effect in niobium/graphite complex systems

Jc increase of MPMG-processed YBa2Cu3O7−x (Y-123) bulk due to fast neutron irradiation

Effect of fast neutron irradiation on magnetic properties of fullerene superconductor Rb3C60

Toshiharu Kubo

Papers

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

Magnetoresistance Effect of Thin Films Made of Single Graphite Crystals (特集 カーボンアロイ学の進展)

Superconducting proximity effect in niobium/graphite complex systems

Jc increase of MPMG-processed YBa2Cu3O7−x (Y-123) bulk due to fast neutron irradiation

Effect of fast neutron irradiation on magnetic properties of fullerene superconductor Rb3C60

Magnetoresistance Effect of Thin Films Made of Single Graphite Crystals (特集カーボンアロイ学の進展)