Tomonori Watanabe

Magnetic field dependence of Jc for Gd-123 coated conductor on PLD-CeO2 capped IBAD-GZO substrate tapes

We prepared GdBa2Cu3O7?? (Gd-123) coated conductors by the pulsed laser deposition (PLD) method on PLD-CeO2/ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate tapes. The Gd-123 film showed a higher critical current density (Jc) in magnetic fields (B) and higher critical temperature (Tc) than those of YBa2Cu3O7?? (Y-123) film. The Gd-123 film exhibited a high Jc value of 0.19?MA?cm?2 at 3?T () in liquid nitrogen (77?K), and the Tc value was 93.8?K. The Jc value at 3?T was twice as high as that of Y-123 film. Moreover, the angular dependence in magnetic fields of Jc for Gd-123 was also superior to that of Y-123. The reduction of Jc by the magnetic field angle for Gd-123 was less sensitive than that in Y-123. Furthermore, Gd-123 clearly exhibited a peak at 0? () as well as at 90? () in the relationship of Jc on the magnetic field angle curve (Jc??), while Y-123 had no peak at 0?. These superior characteristics are considered to be due to the existing defects, such as stacking faults, as observed by transmission electron microscopy. PLD-Gd-123 coated conductors, with pinning-effective defects, high Jc and low anisotropy in Jc??, show promise for future applications.

High critical current density YBa2Cu3O7−δ films on surface-oxidized metallic substrates

Abstract YBa 2 Cu 3 O 7−δ (YBCO) films with high critical current density ( J c ) were fabricated on nickel tapes buffered with bi-axially textured NiO prepared by surface-oxidation epitaxy (SOE). The effects of oxide cap layers, such as YSZ, CeO 2 and MgO, on the SOE-grown NiO were investigated to improve the superconducting properties of the YBCO films on NiO. By inserting a thin MgO cap layer between NiO layer and YBCO film, a J c of 3×10 5 A/cm 2 (77 K, 0 T) was achieved. This result indicates the potentiality of the SOE method. In this paper, the application of the NiO/Ni substrate to non-vacuum processings, such as metal-organic deposition (MOD) and liquid phase epitaxy (LPE) will be also introduced.

New Fabrication Method of High-Jc YBa2Cu3O7 Superconducting Films on Flexible Metallic Substrates

In plane-aligned, c-axis-oriented YBa2Cu3O7 (YBCO) films were deposited on polycrystalline Ni tapes buffered with self-oxidized NiO. The in-plane alignment of the NiO layer was achieved by the oxidation of textured pure (00l)Ni tapes in 1 atm O2 in the furnace. Significant improvement in (00l)NiO texturing was obtained in the temperature range above 1000°C. Pulsed laser deposited YBCO films on the NiO layer were not only c-axis oriented with respect to the film surface, but also strongly in-plane textured. The full width at half maximum of the x-ray diffraction peaks from the (103)YBCO ϕ scan is approximately 11 degrees. This is similar to the values reported with other texturing techniques.

Influence of the second buffer layer for alignment of seed film on Ni tape with NiO buffer layer

Abstract In order to investigate the influence of the buffer layer for the seed film quality which is important to obtain high quality liquid phase epitaxy film, we prepared several different kinds of SmBa 2 Cu 3 O y (Sm123) seed films on SOE-NiO buffered biaxially textured Ni tapes with and without the second buffer layer of BaZrO 3 by the pulsed laser deposition method. As a consequence of the investigation, it was found that BaZrO 3 is a suitable material as a buffer layer to obtain highly in-plane aligned Sm123 seed films on SOE-NiO buffered biaxially textured Ni tapes.

Advances in surface-oxidation epitaxy processed substrates for YBa2Cu3O7−δ film

Abstract The preparation of long oxide template using surface-oxidation epitaxy (SOE) method and the deposition of oxide cap layer and YBa 2 Cu 3 O 7− δ (YBCO) film on it have been studied for the fabrication of coated conductors. In SOE process, Cr-oxide behaves as a barrier against Cr contamination with SOE-NiO layer in high strength and low magnetism Ni-clad Ni–20wt.%Cr (Ni/NiCr) tape. MgO cap layer makes SOE-processed tape surface smooth with the average roughness of a few nm. The critical current ( I c ) of 8 A (the critical current density ( J c ) of 0.2 MA/cm 2 ) was obtained for the YBCO film deposited on a 10 cm long×5 mm width SOE-processed tape with MgO cap layer in a short sample cut from a 10 cm long specimen. J c exceeding 0.1 MA/cm 2 was obtained for YBCO film on SrTiO 3 cap layer and CeO 2 one of SOE-processed tape.

Characterization of YBa2Cu3O7-δ films grown on NiO buffer layer by liquid-phase epitaxy process

Abstract By means of a liquid-phase epitaxy (LPE) process, superconducting YBa2Cu3O7−δ (YBCO) thick film is grown on a biaxially textured NiO buffer layer which is pulsed-laser deposited on a (0xa00xa01) surface of SrTiO3 single crystal. Employment of BaF2-added Ba–Cu–O flux is found to be effective for LPE-YBCO growth because the growth temperature of YBCO is drastically lowered down to 900–920°C compared to the case of usually used simple Ba–Cu–O flux. This strongly suggests that the low-temperature LPE growth of YBCO on a NiO/Ni substrate is hopeful process for coated-conductor production. Superconductivity transition temperature (Tc) of the LPE-YBCO film is measured to be 91 K for onset and 87 K for a zero-resistance state.

Fabrication of seed/buffer layers on metallic substrates for YBCO coated conductors

Abstract LaNiO 3 (LNO) buffer layers with good c -axis orientation on SrTiO 3 (STO), LaAlO 3 (LAO), NiO/STO and SOE (NiO/Ni) tapes were successfully fabricated by the pulsed laser deposition (PLD) method. Biaxially aligned neodymium (NdGaO 3 , NGO) seed layers were successfully fabricated on the STO, LAO and LNO buffer layer by PLD method and post-annealing process. And also, the good biaxial orientation YBa 2 Cu 3 O 7− δ (YBCO) films on NGO seed layers were deposited by liquid phase epitaxy (LPE) method. From this work, it has been proved for the first time that NGO thin film can be used as a seed layer for YBCO thick film deposition by the LPE method. This NGO thin film which is deposited by the PLD method at room temperature and post-annealed at 950°C for 5 h in air, is low cost and very effective for the coated conductor production by LPE.

Fabrication of coated conductor using LPE process

Abstract We tried to apply the LPE process to fabricate RE123 coated conductors. We have been investigating the construction using a BaZrO 3 buffer layer, called “non-reactive buffer type” on the textured Ni substrate. It was confirmed that this construction is stable for the LPE process, because the BaZrO 3 is stable to the RE–Ba–Cu–O solution at the process temperature. First, Y123 was grown on the MgO single crystal substrate with the BaZrO 3 buffer layer in order to confirm the potential of this combination. We confirmed that the BaZrO 3 layer could be effective to prevent from chemical diffusion of Ni and a high superconducting performance cloud be obtained as T c =92 K and J c =2×10 5 A/cm 2 . We prepared with the Sm123 seeded substrate on the BaZrO 3 /SOE/textured Ni, and confirmed that the seed layer and buffer layer showed the fourfold symmetry in the crystal in-plane alignment. Y123 was tried to grow on this sample and it was confirmed that the BaZrO 3 buffer layer prevented from the reaction between the Ni substrate and the solution. Consequently, the Y123 layer with a good in-plane alignment was obtained and it showed high T c value of 90 K.

Fabrication of Assembled Conductor of Bi-Based Multilayered Wires

Setting a goal to apply oxide superconductor to electric power equipment, we have been carrying on with the development of multilayered wires, which are each constituted of oxide layers and silver layers. The multilayered wire is characterized in that low silver ratios and high Jc values are made producible, by thinning and uniforming its superconducting layers, subject to optional wire shapes. For instance, a tape wire with a silver ratio of 1.3 gave birth to a Jc of 21300A/cm2 and an overall Jc (Je) of 9270A/cm2. In the purist of a conductor of a large DC capacity, a layered conductor of 1000A class, which contains 210 tape wires, was developed. This conductor was demonstrated in terms of no quench breaking out with pulses of 2600A-peak. In addition, a stranded conductor of a 100A class containing 6 alumina-fiber insulated round wires was developed and found to have the loss contents consisting mainly of hysteresis loss.

Low temperature formation of YBCO coated conductors on textured metal tapes by liquid phase epitaxy

Abstract We have formed YBCO films on Ag–Cu (2 1 0)〈1 2 0〉 and Ni (1 0 0)〈0 0 1〉 textured metal tapes. By using a furnace equipped with a reel-to-reel tape moving mechanism, continuous coating of YBCO film has been made on the silver-based tape at 925 °C. There were, however, cracks in the film prepared at 925 °C due to penetration of the solvent between the metal substrate and the YBCO film. By reducing the growth temperature to 880 °C, thick films over 5 μm in thickness have grown on the tape with neither intrusion nor reaction at the interface. YBCO film on nickel tape showed that the transition temperature degraded considerably at higher growth temperatures, which is probably due to reaction of Ni with the solution and contamination of Ni in the film.