Ichiro Shigaki

Optimization of single crystal preparation of Bi2Sr2CaCu2Ox superconductor by the travelling solvent floating zone method

Optimization of single crystal preparation of the Bi2.2(Sr, Ca)2.8Cu2.0Oy superconductor by the travelling solvent floating zone method has been performed with the intention of obtaining large single crystals and improving the superconductive transition temperature, Tc. The composition ratio, Sr/Ca, and the oxygen partial pressure of growth atmosphere, PO2 , were varied in the crystal growth. A single crystal typically obtained was a thin plate of the dimensions of 5×50×2 mm3. The thickness of the crystal was the largest in the crystal growth at Sr/Ca=1.4, while no distinct change was observed in the resulting crystals in the range of 22~100 kPa. Electric and magnetic properties, the formal charge of copper ions and existence of ion defects are discussed.

Layer-by-layer epitaxial growth of a Bi2Sr2CuO6 thin film on a Bi2Sr2CaCu2O8 single crystal

The epitaxial growth of a Bi2Sr2CuO6 (2201) thin film on a Bi2Sr2CaCu2O8 (2212) single crystal has been performed using computer‐controlled laser molecular beam epitaxy. The surface of the 2212 single crystal used as the substrate is smooth and invariant under the growth condition at 640 °C in NO2 pressure of 1×10−5 mbar. The growth process of the 2201 film has been observed by in situ reflection high‐energy electron diffraction (RHEED), and the layer‐by‐layer growth of the 2201 phase is confirmed by the oscillation of RHEED intensities. During the growth, a modulated surface structure which is characteristic of the Bi cuprate crystals is always present.

Fabrication of superconducting joints for Bi-2212 pancake coils

To evaluate the possibility of persistent current operation for NMR/MRI using a Bi/sub 2/Sr/sub 2/CaCuO/sub 8/ (Bi-2212) superconductor at 4.2 K, the temperature dependence of magnetic relaxation of the single crystal has been measured. It was found that the operating current must be one-fourth of J/sub c/ at 4.2 K to satisfy the stability condition for NMR/MRI operation ( Delta J/J less than 0.005 ppm/h). A superconducting coil made of Bi-2212 silver-sheathed wire was fabricated by the partial melt growth process. The authors were successful in generating 1.60 T in a zero external magnetic field at 4.2 K with a coil made of silver-sheathed Bi-2212 tape which was 100- mu m thick, 10-mm wide and 150-m long. Superconducting jointed pancake coils with critical current reaching 80 A in an external magnetic field of 1.0 T at 4.2 K were also fabricated.<<ETX>>

Tunneling spectra of Au / Bi2Sr2CuO8 thin film / Bi2Sr2CaCu2O8 single crystal junctions with well defined interface

Abstract Reproducible tunneling spectra of Bi 2 Sy 2 CaCu 2 O 8 single crystals have been obtained using well defined Au / Bi 2 Sr 2 CuO 8 film / Bi 2 Sr 2 CaCu 2 O 8 single crystal junctions which are prepared by laser molecular beam epitaxy. The total shape of the spectra is BCS like and temperature dependence of the gap energy (42meV at 10 K) agrees with the weak-coupling BCS curve. The value of 2D/kT=5.8 obtained here, however, is larger than that predicted by the BCS weak-coupling theory.

1.1 substitution to BlSrCaCuO superconductor

Abstract Li doped Bi 2 Sr 2 CaCu 2 O x single crystals have been obtained by the floating zone method from the starting materials in which less than 20% of Cu atoms are replaced by Li atoms. A single crystal typically obtained is in dimensions 20 × 2 × 0.1 mm 3 . Although the location of Li atoms in the crystal structure remains unclear, incorporations of Li atoms into the crystals as much as 5∼18% in Li/Cu ratios were confirmed by ICP analysis. Inclusion of Li atoms into the structure raises the T c by several degrees, and the highest T c (=93 K ) was attained for the crystal of the highest Li content.

Preparation of Bi2Sr2CuO6 single crystals by the traveling solvent floating zone method

Abstract Preparation of single crystals of the type, Bi2Sr2CuO6 have been undertaken by the traveling solvent floating zone method. Since the polycrystalline material is obstainable as a single phase only at a non-stoichiometric composition, crystal growth throughout this study was concentrated to the composition, Bi2.4Sr1.6CuOx, which yielded a cleaved fragment of the single crystal in dimensions 40 × 6 × 1 mm3. The crystal melts incongruently at around 875†C and exhibits no superconductive behavior above 4.1 K.

Detection of 110 GHz millimeter-wave signal using DyBaCuO step-edge junction

Millimeter-wave detection was investigated using a step-edge microbridge Josephson junction (SEJJ) fabricated by a sputter-deposited DyBaCuO thin film. The SEJJ exhibited a clear response to 110-GHz millimeter-wave irradiation, and Shapiro steps could be observed up to the seventh step. Harmonic mixing detection was successfully achieved using microwaves of 6 approximately 22 GHz as a local oscillation signal. The dependence of conversion efficiency ( eta ) on the harmonic number was expressed as eta varies as N/sup -3.3/. The detector was operative at temperatures up to 65 K, although the efficiency rapidly decreased above 50 K.<<ETX>>

Operation of Bi-2212 Superconducting Magnet with a R.T. Bore of 4 cm in Diameter

Bi-2212 superconducting magnet with a room temperature (R.T.) bore of 45 mm in diameter has been fabricated. The magnet has been cooled by a GM-cryocooler, and it has generated magnetic field up to 0.68 T. In order to prepare a oxide superconducting magnet with such a large R.T. bore, reproducibility in critical current density (Jc) of Bi-2212 silver-sheathed tape must be realized in long rage such as 1500 m. This problem has been solved by extending calcination time of Bi-2212 powder.

Fabrication of Superconducting Coil by Bi2212 Silver Sheathed Tapes

A pancake-coil was successfully made which could generate a 1.6T magnetic field at 4.2K, by applying a partial melt and slow cooling method to wide silver sheathed Bi-2212 tape. The partial melt and slow cooling process was also shown to be effective for making superconducting joints. In order to investigate the possibility of application at higher temperatures, magnetic properties were compared between ion-irradiated and non-irradiated Bi-2212 single crystals. Ion-irradiation was confirmed to be effective for the improvement of an irreversibility field.

Critical current measured by magnetic method and pulsed-transport method

Abstract We have performed two-types of critical current measurements; M-H hysteresis and pulsed-transport method; for the Bi 2 Sr 2 CaCu 2 O x single crystal. The rod which was composed from several single crystal parts was grown by the travelling solvent floating zone (TSFZ) method From the hysteresis measurements, very large critical current density (Jc ab ) of 2.5×10 6 A/cm 2 has been observed at 4.2K. With increasing the temperature, Jc ab decreased rapidly. This rapid decrease corresponds well with the observed small pinning potential. By applying pulsed transport method, larger critical current density than 1.8×10 4 A/cm 2 was observed at 77K.