E. Narumi

Superconducting YBa2Cu3O6.8 films on metallic substrates using in situ laser deposition

In situ laser deposition was used to fabricate YBa2Cu3O6.8 (YBCO) films on metallic substrates. With a buffer layer, YBCO films were strongly c‐axis oriented. Tc = 83 K and Jc= 4000 A/cm2 at 77 K were obtained for a 0.5 μm YBCO film with a 0.15 μm yttrium‐stabilized ZrO2 buffer layer. There was negligible interdiffusion occurring at the interfaces. The n value of YBCO films ranged from 1.4 to 1.5.

Critical current density enhancement in YBa2Cu3O6.8 films on buffered metallic substrates

A transition buffer, consisting of subbuffers grown at different temperatures, was used to enhance the crystallinity and the transport properties of YBa2Cu3O6.8 (YBCO) films on metallic substrates. Films were fabricated using in situ laser deposition and were strongly c‐axis oriented. Critical temperature of 87 K and critical current density of 3×104 A/cm2 at 77 K were obtained for a 0.5‐μm‐thick YBCO film with a 0.2 μm transition yttrium‐ stabilized ZrO2 buffer layer. Also, the magnetic field dependence of Jc could be enhanced by using Pt‐coated metallic substrates.A transition buffer, consisting of subbuffers grown at different temperatures, was used to enhance the crystallinity and the transport properties of YBa2Cu3O6.8 (YBCO) films on metallic substrates. Films were fabricated using in situ laser deposition and were strongly c‐axis oriented. Critical temperature of 87 K and critical current density of 3×104 A/cm2 at 77 K were obtained for a 0.5‐μm‐thick YBCO film with a 0.2 μm transition yttrium‐ stabilized ZrO2 buffer layer. Also, the magnetic field dependence of Jc could be enhanced by using Pt‐coated metallic substrates.

Superconducting YBa sub 2 Cu sub 3 O sub 6. 8 films on metallic substrates using in situ laser deposition

In situ laser deposition was used to fabricate YBa2Cu3O6.8 (YBCO) films on metallic substrates. With a buffer layer, YBCO films were strongly c‐axis oriented. Tc = 83 K and Jc= 4000 A/cm2 at 77 K were obtained for a 0.5 μm YBCO film with a 0.15 μm yttrium‐stabilized ZrO2 buffer layer. There was negligible interdiffusion occurring at the interfaces. The n value of YBCO films ranged from 1.4 to 1.5.

Processing of Bi2Sr2CaCu2Ox thick films from nitrate precursors

High‐quality Bi2Sr2CaCu2Ox/Ag superconducting tapes were fabricated directly from the nitrate salts of Bi, Sr, Ca, and Cu by the partial‐melt‐growth technique. Nitrate particles were deposited electrostatically on the Ag substrate and heat treated. After process optimization of the superconducting tapes, the best samples showed typical Tc of 89 K with zero applied field critical current density of 2×104 A/cm2 (Ic=11.2 A) at 77 K and 2.6×105 A/cm2 (Ic=190 A) at 4.2 K. Unlike films grown using solid state reacted precursor powders, these films lacked the typical Bi‐free, needlelike defects and possessed a smooth morphology. X‐ray diffraction patterns showed the film to be highly c‐axis oriented. The processing of these tapes significantly reduces the overall fabrication time from precursor materials preparation to final heat treatment.

In-plane texturing and its effect on critical current densities of YBa2Cu3O7−x thin films grown on polycrystalline substrates

Abstract It is demonstrated that on polycrystalline substrates, a - b plane textures of c -axis oriented YBa 2 Cu 3 O 7− x (YBCO) thin films can be controlled with biaxially aligned yttria-stabilized zirconia (YSZ) buffer layers grown by ion beam-assisted pulsed laser deposition. An X-ray φ scan measurement shows that the in-plane alignment of the a - (or b -) axes in polycrystalline YBCO thin film is determined by the in-plane texture of YSZ buffer layer. The transport critical current density ( J c ) of the YBCO thin film was found to directly correlate with its degree of in-plane alignment characterized by the full-width at half-maximum (FWHM) of YBCO (103)/(013) φ scan profile. For a YBCO thin film with the FWHM of 27°, J c shows an order of magnitude increase in comparison to YBCO thin films with a random in-plane distribution of a - and b -axes. Using a numerical method to describe the distribution of the a - (or b -) axes of YBCO grains, the misorientation angles of the grain boundaries were determined, and the transport critical current densities of polycrystalline YBCO thin films were calculated. The results are in good agreement with the experimental J c data for samples with different degrees of in-plane alignment. It indicates that the reduction of the number of high-angle grain boundaries is the main reason for the improved J c observed in the biaxially aligned YBCO thin films.

Plasma-assisted laser deposition of YBa2Cu3O7-δ

The change in superconducting properties due to the presence of a bias electrode in in situ laser deposition was explored. It was found that the bias ring allowed a 50–70 °C reduction in the deposition temperature. This reduction is correlated to an increase in ion current impinging on the substrate.

Pressure dependence of Bi-Sr-Ca-Cu-O phases with laser deposition technique

Superconducting Bi2Sr2Can−1CunOx (n=1,2,3) films, with the c‐axis perpendicular to the films, were fabricated by laser deposition. Oxygen pressure was found to be important to control the phases, and a unique pressure dependence of Bi‐Sr‐Ca‐Cu‐O phases was shown by these films. Tc of 76 K and Jc of 1.5×105 A/cm2 at 40 K were achieved for the in situ Bi2Sr2CaCu2Ox film. The critical‐current densities in the external magnetic field up to 5 T with the fields parallel and perpendicular to the c‐axis of the film were measured.

Predictive model for critical current density of Ag-sheathed Bi2Sr2Ca1Cu2O8 composite tapes with fabrication defects

Abstract Fabrication of long Ag-sheathed Bi 2 Sr 2 Ca 1 Cu 2 O 8 composite tapes is sometimes accompanied by the distribution of large bubble-type defects located at relatively uniform intervals along the length of the conductor. The size, shape and number of these defects dictate the critical current density and eventually the overall quality of the tape. The effect of defect size and concentration on the overall critical current density is theoretically modelled. Using experimental data on the transport properties of short conductor samples with a defect of known dimensions, the model can be used to predict the critical current density of a long conductor tape by visual inspection of the number, size and location of these defects along the conductor length.

rf plasma‐generated superconducting Y1Ba2Cu3O7−x films

Using an inductively coupled rf plasma operated at atmospheric pressure, superconducting thin films of Y1Ba2Cu3O7−x have been grown in situ on single‐crystal yttria‐stabilized zirconia [100] from an aerosol precursor. X‐ray diffraction and rocking curve results indicate that the films are highly c‐axis oriented normal to the substrate with a lattice constant of 11.67–11.68 A. The full width at half maximum of these films ranges from 0.55° to 1.0°. The films have typical Tc’s of 86 K and Jc’s in excess of 105 A/cm2 at 77 K and zero field; magnetic measurements reveal an anisotropy of 3:1 at 69 K. The dependence of the processing parameters on the transport properties of the superconducting films is discussed.

Transport properties of YBa2(Cu0.98M0.02)3Oy(M = Fe, Co, Ni) superconducting thin films

Critical current densities of YBa2(Cu0.98M0.02)3Oy (M = Fe, Co, Ni) superconducting thin films made by laser ablation are investigated as a function of temperature and magnetic field. Jc in magnetic field shows that Ni-doping has a large effect on intragranular current while Fe-doping seems to have more influence on intergranular coupling. All three dopants give rise to basically same field-dependence of their volume pinning force Fp at elevated temperature (T = 60 K) except in the low field region (H < 2 T), and Fp can be scaled to a universal function Fp/Fp.max = b(1−b)2. Hall effect measurements show that the effective carrier concentration is lower than that in undoped material.