Yuji Yaegashi

Transport critical current in silver sheathed BiPbSrCaCuO tapes

The temperature and magnetic field dependences of transport critical current density, J/sub c/, in silver-sheathed Bi/sub 2.1/Pb/sub 0.4/Sr/sub 2.2/Ca/sub 3.4/0/sub 4.2/ tapes have been studied. J/sub c/ was weakly dependent on magnetic fields at temperatures below 30 K. The effect of field-variation history on J/sub c/ was observed in the same temperature region. The magnetic field dependence of J/sub c/ and its anisotropy with respect to the field direction increased rapidly with increasing temperature. The irreversibility field and its anisotropy were also studied. Flux pinning and weak coupling properties are discussed.<<ETX>>

Crystal Structure Refinement of the Oxygen-rich RCuO2+δ(R=Y and La) Delafossite by Neutron Diffraction

We have refined the structural parameters of delafossite-type cuprates, i. e. (Y0. 95Ca0.05)CuO2. 02 and LaCuO2.02 as well as the derived phases containing excess oxygen, i. e. (Y0. 95Ca0.05)CuO2. 49 and LaCuO2.64 from powder neutron diffraction data at room temperature. According to Rietveld analyses, (Y0.95Ca0.05)CuO2.02 and LaCuO2.20 delafossites could be analyzed with space groups of P63/mmc and R3m, respectively. The metal- and oxygen-atom lattices were perfectly stoichiometric and there was no major stacking faults in the phases. For (Y0.95Ca0.05)CuO2. 49’ the structure was refined in the P63/m space groups with sufficient R-factors, as previously proposed by Sora et al. The excess oxygen atoms are likely located in the distorted triangular Cu plane.

Synthesis and Magnetic Properties of Rare-Earth Cuprates R2Cu2O5 (R=Y, Tb, Dy, Ho, Er, Tm, Yb and Lu)

We investigated the structural and magnetic properties of R2Cu2O5 (R=Tb, Dy, Ho, Y, Er, Tm, Yb and Lu) compounds. Polycrystalline samples of R2Cu2O5 were successfully synthesized by a solid state reaction technique. Powder x-ray diffraction patterns revealed that every sample was isostructural of an orthorhombic unit cell and a nearly single-phase compound. The lattice parameters were found to be decreased quasilinearly with decreasing the lanthanide ionic radius. Except for Tm2Cu2O5, the magnetic susceptibilities decreased antiferromagnetically for most of R2Cu2O5 compounds at temperatures below ~30K.

Effect of Fabrication Process on Jc of Ag-Sheathed (Bi, Pb)SrCaCuO Tapes

Transport critical currents of Ag-sheathed (Bi, Pb)SrCaCuO tapes produced by a so-called powder-in-tube method were measured in the temperature range from 5 to 77K and in magnetic fields up to 8T. Comparing J c in tapes rolled to 0. 1 and 0.25mm in thickness and sintered, followed by the cycle of press and sinter, the thicker tapes showed slightly lower J c at all temperatures and magnetic fields. Anisotropy of J c increased with increasing temperature and magnetic field above ∿30K. Below ∿30K, it is relatively small for all tapes. The history effect was observed below ∿40K for tapes 0. 1mm in thickness. However, the temperature at which it appeared seemed to increase slightly for thicker tapes with lower J c.

Uniformity on Transition Temperature and Composition in Sputtered Y-Ba-Cu-O Films

Uniformity in Y-Ba-Cu-O (YBCO) films has been investigated on transition temperature Tc and composition. YBCO films with thicknesses of 100–150 nm have been prepared on the substrate of single crystal MgO heated around 800°C by on-axis dc magnetron sputtering using a single sintered target. Their zero resistance transition temperature Tc , end of typical films is in the range of 82–85 K. There is a change of Tc in films of a 100 mm2 area. A portion over the target center shows normally a lower Tc value than other portions by about 3K and has an expanded c-axis lattice parameter. The composition change is also seen in films, and the Cu content is somewhat larger for the portion indicating a lower Tc value.

Characteristic change of sealing rubber due to usage time

Gas insulated switchgear (GIS) is a compact metal encapsulated switchgear consisting of high-voltage components such as circuit-breakers and disconnectors, which can be safely set up in confined spaces. However, some GISs have been used for more than 40 years, so characteristic of sealing rubber is considered to be degraded. We find possibility of aging of the sealing rubber by comparing surface characteristics of an aging sealing rubber and that of a new one. We used three methods to analyze the characteristics of aged sealing rubber and that of a new one. The methods we used are SEM-EDX analysis, FTIR spectroscopy and tensile test. From the SEM-EDX analysis, we found that the unevenness appeared on the surface of aging one as the filler of the rubber material may appear on the surface. From the FTIR spectroscopy, we found that a new peak appears at wave number 1050 nm, 1250 nm and 1750 nm so we consider that 1050 nm and 1250 nm are a bond of C-O, so oxidative deterioration is proceeding possibly. And the peak near the wavenumber 1750 is disappeared for aged sample of No.46. Since the peak near wave number 1750 shows a double bond, there is a possibility that the double bond was cleaved by the addition reaction. From the tensile test, we found that the aging one is breaking with a smaller strain than the new one but the slope of the graph (Youngs modulus) is approximately equal, so we consider that tensile stress leading to breaking of aged one is smaller than that of new one but the elastic force of the sealing rubber has not changed greatly since the Youngs modulus is approximately equal. Therefore, although the surface is oxidized probably, we found that there is little influence on the gas sealing performance since the elastic force of the sealing rubber is not decreased so much.

In-Plane Alignment in C-Axis Oriented Y-Ba-Cu-O Films Prepared on MgO(100) by On-Axis DC Magnetron Sputtering

The in-plane alignment of Y-Ba-Cu-O(YBCO) films which were prepared on the (100) plane of single crystal MgO in an argon-oxygen atmosphere by on-axis dc magnetron sputtering was investigated. The growth of c-axis oriented films were examined by mainly adjusting substrate temperature Td and oxygen partial pressure Po. As compared to the a-axis oriented films, the c-axis oriented ones are formed at higher temperatures. There exist YBCO grains with the a(or b)-axis parallel to MgO [100] and 45°-rotated ones in the c-axis oriented films. The 45°-rotated grains are apt to grow at higher temperatures. The critical current density Jc is appreciably reduced in films consisting of YBCO grains of both types.

Sputter-Deposition of Homogeneous Y-Ba-Cu-O Films and Their Superconducting Properties

The effects of cooling process just after deposition and of magnetic field near target electrode in preparing homogeneous Y-Ba-Cu-O(YBCO) films by on-axis dc magnetron sputtering using a single sintered target have been investigated. The magnetic field affects sputtering voltage which is connected with deposition rate. The cooling process in an oxygen atmosphere has a great influence on the growth of YBCO grains. The zero resistance transition temperature Tc,end and critical current density Jc at 77 K and 0 T of films prepared on the optimum conditions reach 85 K and 5×105 A/cm2, respectively.

Anisotropy of Resistivity and Critical Current Density in Y1Ba2Cu3O7−y Films

We studied the anisotropy of the resistivity and the critical current density in thin films of Y1Ba2Cu3O7−y at various temperatures and magnetic fields. Below 70K, a local minimum of the resistivity for the magnetic field direction parallel to the c-axis became apparent at a high current density. A sharp peak of the critical current density and an inverse decrease of the resistivity were observed in the narrow range of the magnetic field direction parallel to the ab-plane. The results might be ascribed to the intrinsic flux pinning mechanism.

Critical Current Density and Flux Pinning in Silver Sheathed BiPbSrCaCuO Tapes

Transport critical current densities in silver sheathed BiPbSrCaCuO tapes were measured at various temperatures and magnetic fields. The critical current properties are discussed on the basis of a scaling law of the flux pinning. The irreversibility field was also measured and compared with the collective flux creep thoery.