Hajime Hitotsuyanagi

Ag-Sheathed Bi-Pb-Sr-Ca-Cu-O Superconducting Wires with High Critical Current Density

Critical current density (Jc) and its dependence on magnetic field in Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wire was improved by grain alignment and homogenization of the high-Tc phase (110 K). The maximum transport current density at 77.3 K in a zero magnetic field was increased to 6930 A/cm2. The magnetic field dependence of Jc (0.1 µV/cm criterion) was summarized as follows: 1660 A/cm2 (I ⊥H, a-b plane ∥H, 0.1 T), 900 A/cm2 (I ⊥H, a-b plane ⊥H, 0.1 T). We found that the grain boundaries were bonded strongly in the direction of alignment.

Electromagnetic properties and morphology of Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wires

The critical current density (Jc) in Ag-sheathed Bi-Pb-Sr-Ca-Cu-O superconducting wire increased to 17,400 A/cm2 in a zero magnetic field. The magnetic field dependence of Jc was improved according to the increase of Jc in a zero magnetic field. Fine, dispersed, nonsuperconducting phases were observed through SEM and TEM. These phases are expected to act as pinning sites.

Amorphous-Si1−xSnx:H by sputter assisted plasma CVD☆

Amorphous Si1−xSnx:H films were deposited by Sputter Assisted Plasma CVD (SAP-CVD) which used glow discharge to decompose silane gas and to sputter a solid tin target simultaneously. Resulting films contain tin as 0<x<0.5 analysed by Auger spectroscopy. Dark conductivity changes from 5×10−10 (ohm-cm)−1 to 1.0 (ohm-cm)−1 as 0<x<0.5. Optical band gap decreases monotonically from 1.8 eV to 0.2 eV, as x increases from 0 to 0.5.

Superconductivity of Ba2Y(Cu, Ti)3Oy Oxide

Samples of Ba2Y(Cu, Ti)3Oy oxide were synthesized and the effect of substituting Cu with Ti was studied. In the Ba2Y(Cu3-xTix)Oy (0x0.9), specimens were obtained which indicated a Tc of over 80 K. In the composition BaαYCuβTi0.6Oy (1.9α2.3, 2.3β3.5), some (Cu Ti)-rich samples indicated a Tc of over 95 K which was as high as that of the existing Ba2YCu3Oy. Diamagnetic signals measured by AC susceptibility at room temperature were detected in some specimens. Zero electric resistance was observed (<10-4 Ωcm at our experimental resolution) up to 300 K in the composition Ba2YCu2.4Ti0.6Oy sintered at 940°C.

Electromagnetic Properties and Structures of BiPbSrCaCuO Superconducting Wires

High-Jc silver-sheathed BiPbSrCaCuO superconducting wires were fabricated through the solid reaction method. These wires showed the maximum Jc of 2.5X 104 A/cm2 (77. 3K) in a zero magnetic field and 1.2X104 A/cm2 at 0.1 Tesla. Key factors for high-Jc wires are: dominant high-Tc phase, highly oriented structures, good bonding at grain boundaries and fine dispersion of non- superconducting phases. When the wire was immersed in liquid helium, maximum Jc of 3.8X104 A/cm2 at 23 Tesla was achieved. 50cm length conductors were fabricated. These conductors were tested and proved to have Ic of practical levels; 170 A at 77.3K and 1000 A at 4.2K. These results show the promising potential of silver-sheathed BiPbSrCaCuO superconducting wires.

Superconducting Wires of High Tc Oxides

Superconducting wires of Y–Ba–Cu–O system have been investigated. Wires were fabricated by powder method. The wires were successfully reduced to a small diameter. Wires of Y1Ba2Cu3O7 exhibit zero resistance at 90 K.

Amorphous Silicon—Germanium Deposited by Photo—CVD

Hydrogenated amorphous silicon germanium (a—SiGe:H) films were deposited by photo—chemical vapor deposition (Photo—CVD) of SiH4 and GeH4 with mercury sensitizer. Their band gap was controlled from 0.9 eV to 1.9 eV by changing the gas ratio of SiH4 and GeH4. High quality opto—electrical properties have been obtained for thea—SiGe:H films by Photo—CVD. Hydrogen termination and microstructure of a-SiGe:H were investigated by infrared absorption and transmission electron microscopy. Ana—Si:H solar cell and an a—Si:H/a—SiGe:H stacked solar cell were made, each of which has conversion efficiency 5.3% and 5.1%, respectively.

Development of High Tc Superconducting Wire by Powder Method

Ag-sheathed high Tc superconducting wires of YBa2Cu3O7-x and Bi0.8Pb0.2SrCaCU1.5Ox were developed. Improvements in the density and the orientation of crystals brought about by press processing have been investigated, and by adopting adequate processing procedures the critical current densities were increased up to 4140A/ cm2 and 4400A/ cm2 for Ag-sheathed YBa2Cu3O7-x and Bi0.8Pb0.2SrCaCu1.5Ox superconductors, respectively.

Preparation of Bi System Oxide Superconductors by Melt Growth

BiSrCaCuO superconductors were prepared by several directional-solidification methods: the melt extraction method, the horizontal bridgman method and the laser pedestal growth method. Temperature gradient was an important factor in obtaining highly aligned crystal structures. In the case of the laser pedestal growth method, Tc of 87K and Jc of 3070A/cm2 (77.3K, OT) were obtained. A Tc above 100K was achieved when a Pb added sample by the laser pedestal growth method was annealed.

Growth and Superconducting Properties of Y1Ba2Cu3O7-δ Thin Films Sputtered on Flexible YSZ Substrates

Y1Ba2Cu3O7-δ. thin films were grown on polycrystalline, flexible YSZ substrates by RF magnetron sputtering. A Tc(R=0) of 90.3 K was obtained after annealing as the highest value. The films had c-axis orientation and were composed of islands even at a film thickness of 2.4 μm. The islands were partially impinged on each other. Jc largely depended onthe degree of island impingement. A Jc value of 1.2×104 A/cm2 was obtained on the film on which the islands mostly impinged on each other during annealing. By bending these films, the effect of strain on the superconducting properties was investigated. Tc(R=0) values raised as the compressive strain increased up to 0.3%, though they were lowered as the tensile strain increased. Jc did not degrade under a compressive strain of 0.3%, though it degraded by 33% under a tensile strain of 0.3%.