Noriyuki Yoshida

Low-energy ion scattering spectroscopy observations of c-axis-oriented YBa2Cu3O7-x thin films : effects of in-vacuum annealing

The atomic structure of (001) surfaces of c‐axis‐oriented YBa2Cu3O7−x (YBCO) thin films was studied by low‐energy ion scattering spectroscopy (ISS) after annealing in ultrahigh vacuum. This is the first report on the surface analysis of superconducting oxide evaluated by ISS. A clean surface of YBCO (001) 1×1 is produced by annealing at around 500 °C. The surface structure is discussed in terms of the blocking and the nonblocking effects caused by the desorption of O(4) atoms. We conclude that the (001) surfaces are stabilized by Cu(1)‐O chains.

Surface Analysis of C-Axis-Oriented YBa2Cu3O7-X Thin Films by QMS, XPS and LEED: Effects of In-Vacuum Annealing

The effects of in-vacuum annealing on the crystallinity and superconductivity in the surface region of YBa2Cu3O7-X thin films were investigated by QMS, XPS and LEED. Contaminated and disordered layers, which were nonsuperconducting phase, covered the film surface after being exposed to air. Surface contaminants are removed by annealing at 350°C in ultra high vacuum. The orthorhombic YBa2Cu3O7-X(001) structure and superconducting phase are obtained at the outermost surface after annealing at 350-400°C.

Fabrication of a high current superconductor in Y-system by excimer laser ablation

A hundred pieces of thin film Y1Ba2Cu3Ox(YBCO) superconducting tape, each of which was 1.1meter long, were fabricated using KrF excimer laser deposition. Almost all the tapes had Jc values more than 1.0×104 A/cm2. The best data showed the Jc of 4.5×104A/cm2 and the Ic of 4.3A at 77.3K for 1.1m voltage tap spacing. The sixty tapes were spirally wound in six layers on a stainless steel former to assemble a high current conductor. The Jc of 1.8×104A/cm2 and the Ic of 103A were achieved for 1.0m in length of the conductor. With the Jc improvement, process conditions of the YBCO deposition were refined. The Jc of 1.0×105A/cm2 is obtained for a short sample. Morphological features of the high Jc film are also discussed.

Silver Halide Fiber For Transmitting A CO2 Laser Beam

The silver halide fiber for transmitting a CO2 laser beam using the mixture crystal of silver bromide and silver chloride is described. The silver halide is purified by zone melting. The absorption coefficient of its preformed crystal measured by a CO2 laser calorimeter is less than 1.0x10-4 cm-1 . The silver halide fibers whose diameters are 0.5 to 0.7mm are made by hot extrusion. The transmission loss of silver halide fiber is 0.07dB/m when measured by a CO2 laser beam. The measured spectral transmission lgss due to scattering inside and on the surface of the fiber is nearly proportional to λ -2 where λ is the wavelength, and it is low in the infrared wavelength region, ranging from a few microns to over ten microns. Because of its excellent resistance to optical damage and bending as well as other characteristics important to practical application, silver halide fiber is suitable for use in CO2 laser power transmission. It is also expected to he an optical waveguide in the field of infrared optic sensors.

Intergranular transport properties in c-axis oriented YBa2Cu3Oy polycrystalline films

The current–voltage (I–V) characteristics and the resistive transition under magnetic field were extensively investigated on c-axis oriented YBCO polycrystalline films with a different amount of an in-plane grain alignment. All the parameters deduced from the scaling analyses in the intergranular region along with the vortex-glass-to-liquid transition indicate that the intergranular current transport is not via weak links but is due to strongly coupled channels regardless of a degree of an in-plane grain alignment.

Characterization of Bi2Sr2CaCu2Ox Superconducting Rods and Tapes

Highly oriented superconducting rods or tapes of Bi2Sr2CaCu20x have been developed. The rods were grown by laser pedestal growth method. The Ag composite tapes were prepared by partial melt method.

Transport properties and in-plane alignment of YBaCuO films

Abstract We report on the structure difference in YBaCuO films deposited on MgO(001) and mirror polished polycrystalline YSZ substrates. The critical current density of the film on polycrystalline YSZ is two orders lower than that on MgO(001). To improve this J c value, the substrate with relief structure was employed. This relief modification of substrate surface was found to be effective in controlling the in-plane alignment of the film grains deposited on it.

R&D on HTS Wires in the Super-GM Project

The HTS wires have been developed for the application to electric power apparatuses in the Super- GM project. We made steady progresses in the fundamental wire characteristics and fabricated some trial products toward applications. The current capacities and the critical current densities of the Bi-2223, Bi-2212, Tl-1223 and Y-123 wires have been improved. A IkArms class AC lead and two types of Y-123 current limiting elements were trially fabricated and their properties were examined. As for the evaluation technique, Abrikosov decorated pattern of magnetic flux lines was observed for a Bi2212 single crystal using Bitter decoration technique.

In Situ Observation of Phase Changes in Bi2212 Superconducting Tapes by High Temperature X-ray Diffraction

High-temperature X-ray diffraction has been used to investigate an aspect from partial melting state to crystallization for Bi2Sr2Ca1Cu2Oz tapes. When a sample having a nominal composition of Bi2Sr2Ca1Cu2Oz was heated in air, the simple XRD pattern that is, (Sr,Ca)1Cu1O2 and liquid, in partial melting state was observed and the XRD pattern nearest to single phase of 2212 was obtained. When the same sample was heated in oxygen, Bi-(Sr,Ca)-O and Bi-2201 phases additional to (Sr,Ca)1Cu1O2 largely remained in partial melting state. Such phases were hard to react and precipitated after transformation to the 2212 phase. The Ag addition was effective to reduce impurity phases in oxygen cooling.

Research on Oxide Superconducting Wires for Application to Power Apparatuses

Super-GM has been conducting R&D on oxide superconducting wires for application to power apparatuses since 1988. Various wires have been developed using Y, Bi and T1-based materials by Jelly Roll, plasma spraying, laser pedestal growth, ionized cluster beam, laser ablation and CVD methods. The Jc value in each short sample of wires manufactured by these methods is more than 104A/cm2 at 77K,OT. Especially, the Jc value of more than 105A/cm2 has been achieved in each wires manufactured on a polycrystalline metal by the laser ablation and the CVD methods. Moreover, for application to power apparatuses, some models of solenoid coil, current lead and fault current limiter have been manufactured by the Jelly Roll, the laser pedestal growth and the ionized cluster beam methods respectively. The basic operating characteristics of the models have been successfully proven.