Ataru Ichinose

Critical current control in YBa2Cu3O7-δ films using artificial pinning centers

High-temperature superconductors can carry high non dissipative currents at low temperatures as long as quantized vortices are pinned. However, the currents in a magnetic field at liquid nitrogen temperature (77 K) are not sufficiently high for practical use due to the weak pinning. For the improvement of nondissipative currents in YBa2Cu3O7-δ films, linear defects that extended to the c-axis of the film were introduced using a novel nanostructure technology. We observed a marked enhancement of the nondissipative currents even at 77 K and high fields when the fields were applied close to the c-axis. This is a clear demonstration of enhanced pinning using artificially incorporated pinning centers.

New superconducting cuprates (Pb, Cu)(Eu, Ce)2(Sr, Eu)2Cu2Oz

Abstract New superconducting Pb-based layered copper oxides, (Pb, Cu)(Eu, Ce)2(Sr, Eu)2Cu2Oz, have been synthesized. This new superconducting phase or the “1222” phase characteristically contains a (Pb, Cu)-O monolayer and a “fluorite-type” block layer which is sandwiched between the basal planes of double Cu-O5 pyramids. Crystallographycally, this structure agrees with that recently proposed for nonsuperconducting PbPr2.4Sr1.6Cu2.6Oz by Adachi et al. A superconductivity transition with the onset temperature of 25 K is measured for the nearly single-phase sample of the nominal composition of ( Pb 1 2 Cu 1 2 ) ( Eu 3 4 Ce 1 4 )2( Sr 7 8 Eu 1 8 )2Cu2Oz. This is the first superconductor of the “1222” structure.

Microstructures and critical current densities of YBCO films containing structure-controlled BaZrO3 nanorods

BaZrO3 nanorods are known to be effective pinning centers as c-axis-correlated pinning centers. Furthermore, BaZrO3 nanorods in REBa2Cu3Oy (RE: rare-earth element) films are formed by self-assembled stacking of BaZrO3 using a target mixture of a superconductor and BaZrO3 for pulsed-laser deposition, which is a very easy fabrication technique. The density of BaZrO3 nanorods in YBa2Cu3Oy (YBCO) films can be controlled by varying the BaZrO3 content in a target. The BaZrO3 addition has two functions for superconductivity; one is the improvement of pinning forces due to the addition of pinning centers and the other is Tc degradation. The optimum BaZrO3 addition for Jc improvement in magnetic fields is found to be around 3 wt% because of a trade-off between the two functions described above. Furthermore, the length of BaZrO3 nanorods is found to be controlled using two types of target: pure YBCO and a mixture of YBCO and BaZrO3. Varying the BaZrO3 nanorod length has an effect on the pinning mechanism. In particular, magnetic field angle dependences of Jc are varied from c-axis-correlated pinning to nearly random pinning by changing the nanorod length. The magnetic field at the crossover of the pinning mechanism seems to be adjusted by the BaZrO3 nanorod length.

Critical Current Density Enhancement around a Matching Field in ErBa2Cu3O7-δ Films with BaZrO3 Nano-Rods

Field angular dependences of critical current density are measured for as-grown high crystalline quality ErBa2Cu3O7-δ films with BaZrO3 nano-rods. Large critical current density enhancement is observed. The magnetic field where the enhancement is observed coincides with the matching field calculated from the density of BaZrO3 nano-rods. The largest enhancement is observed in B ∥c-axis of ErBa2Cu3O7-δ films. This anisotropic critical current density enhancement is thought to be caused by the direction of BaZrO3 nano-rods which grow along the c-axis of the films. BaZrO3 nano-rods in the films will promise the application of coated conductors in a magnetic field.

Systematic Comparison of Eight Substrates in the Growth of FeSe0.5Te0.5 Superconducting Thin Films

We have investigated the crystal structures and superconducting properties of thin films of FeSe0.5Te0.5 grown on eight different substrates. Superconductivity is not correlated with the lattice mismatch; rather it is correlated with the degree of in-plane orientation and with the lattice parameter ratio c/a. The best superconducting properties were observed in films on MgO and LaAlO3 (Tczero of 9.4 K). Transmission electron microscopy observation showed that the presence or absence of an amorphous-like layer at the substrate surface plays a key role in determining the structural and superconducting properties of the grown films.

Epitaxial Growth of FeSe0.5Te0.5 Thin Films on CaF2 Substrates with High Critical Current Density

In-situ epitaxial growth of FeSe

New families of layered cuprates containing double-MO2-unit fluorite blocks: (Ho, Ce)3Sr2Cu3O11 and (Ho, Ce)3Sr2Cu2 (Cu, M)O11 (M = Pb, Fe, Al)

_{0.5}

Phase stability and decomposition of superconductive YBa2Cu4O8

Te

Microstructure of electron-beam-evaporated epitaxial yttria-stabilized zirconia/CeO2 bilayers on biaxially textured Ni tape

_{0.5}

Jc improvement by double artificial pinning centers of BaSnO3 nanorods and Y2O3 nanoparticles in YBa2Cu3O7 coated conductors

thin films is demonstrated on a non-oxide substrate CaF