Gd2Zr2O7 Research Articles

Nano–nano composite powders of lanthanum–gadolinium zirconate and gadolinia-stabilized zirconia prepared by spray pyrolysis

Ceramics with structure on nanometer-length scales have a thermal conductivity much lower than their coarser-grained ceramics. But the relatively low activation energy for grain growth of nanoparticles limits the stability of nano-material at high temperatures. The objective of the present study was to investigate the preparation of the composite powders of nano (La,Gd)2Zr2O7 and nano (Zr,Gd)O2−δ by a sol-spray pyrolysis method. The XRD results indicated that the reaction products of 0.2LaO1.5–xGdO1.5–(0.8−x)ZrO2 (0.15≤×≤0.25) ternary system were composed of pyrochlore (La,Gd)2Zr2O7 and cubic (Zr,Gd)O2 phases. The composition with 0.2LaO1.5–0.2GdO1.5–0.6ZrO2 had a grain size much smaller than the lower GdO1.5 content counterpart for both the (La,Gd)2Zr2O7 and (Zr,Gd)O2−δ phases. The relationship between grain size and GdO1.5 content was explained in terms of lattice matching.

Effect of $\hbox{Y}_{2}\hbox{O}_{3}$ Seed Layer on Epitaxial Growth of Oxide Barrier Layer for YBCO Coated Conductor

Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> film was deposited as the seed layer by dc reactive sputtering technique on a Ni-5at%W (NiW) substrate. The subsequent oxide buffer layers were introduced as well such as Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (GZO) and La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (LZO). The effects of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> seed layer on the epitaxial growth of buffer layers and the performance of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) films were investigated. The atomic force microscopy images showed that the surfaces of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> seed layers were homogeneous and flat with the root mean square roughness of about 1.2 nm, which is significant for the subsequent layers. In contrast, root mean square roughness values of GZO films on bare NiW or Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> seeded NiW were normally about 2.7-3.4 nm. A series of X-ray studies indicated that the GZO and LZO oxide barrier layers on Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> can be epitaxially grown easily with a wide processing condition of water vapor partial pressure. Furthermore, the effect of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> seed layer on subsequent YBCO films was investigated by comparing the transition temperature Tc and the critical current density .Ic between YBCO/GZO/NiW and YBCO/GZO/Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /NiW. These results demonstrate the notable role of the Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> seed layer, not only on high-efficiency production of subsequent functional, but also on the improvement of superconducting performances of YBCO films.

A Review of the Ion Beam Assisted Deposition Researches towards Industrialization for the Second Generation High Temperature Superconducting Wire Fabrication

on beam assisted deposition (IBAD) is an important technique to fabricate the second generation high temperature superconducting (2G HTS) wires. Among the fabrication routes of 2G HTS long wires, IBAD route achieved the best performance in recent years. IBAD was adopted in this field in 1991 to obtain biaxially textured buffer layers, which helped to deposit high quality YBCO superconducting films on metallic substrates for the first time. Series of experimental and industrial researches on IBAD were carried out by many groups worldwide. And in the researches lasting for over two decades, the focused material for IBAD was changed from Yttria-Stabilized Zirconia (YSZ), Gd2Zr2O7 (GZO) to MgO. In this paper, the research progresses and the main achievements were briefly reviewed.

Surface engineering of biaxial Gd2Zr2O7 thin films deposited on Ni–5at%W substrates by a chemical solution method

The surface texture and morphology of thin films play an essential role in determining their properties. In this study, local features in the film surface of crystallized Gd2Zr2O7 (GZO) films with a thickness gradient are investigated by means of scanning electron microscopy and electron backscatter diffraction. A strong dependence of the morphology and texture on the film thickness is observed, mainly due to (i) the transition of growth mode associated with the critical film thickness, i.e., increasing the film thickness leads to the grain morphology changing from 2-dimensional discs (highly ordered nanoislands or network) to 3-dimensional domes (equiaxed nanograins), and (ii) the segregation of residual carbon in the surface layer. The epitaxial nuclei forming at the interface hardly further develop by consuming the polycrystalline grains in the surface layer. A two-step annealing procedure is proposed to improve the surface texture in the GZO/NiW system, according to the influence of PO2 on the texture formation of GZO films. A GZO film with strong biaxial texture is achieved, as evidenced by the high indexing rate of Kikuchi patterns on the film surface, as well as by the highly ordered crystal structure along the film thickness observed by a transmission electron microscope. On the basis of the enhanced understanding of the crystallization processes, we demonstrate a possibility of engineering the surface morphology and texture in the film deposited on technical substrates using a chemical solution deposition route.

Development of Long Length IBAD-MgO and PLD Coated Conductors

For high speed and low cost production of coated conductors, a simplified 4-layered buffer architecture consisting of Gd2Zr2O7 (GZO)/Ion Beam Assisted Deposition (IBAD)-MgO/LaMnO3/CeO2 was realized, which is compared with the conventional 5-layered IBAD-MgO buffer layers. A new cation diffusion barrier and nucleation GZO layer was first reported. The fourth layer of Pulsed Laser Deposition (PLD)-CeO2 showing the self-epitaxial growth effect resulted in the in-plane texturing (Deltaphi) of about 3 to 4 degrees. Consequently, high critical current, Ic, values above 600 A/cm-width were attained for PLD-GdBa2Cu3O7-X (GdBCO) short samples. Using this result, a 41 m long GdBCO coated conductors was successfully fabricated at the production rate of 24 m/h for IBAD-MgO. This conductor exhibited superior Deltaphi values of 3.7 to 3.8 degrees and high Ic values of 500 to 600 A/cm-width at 77 K and self -field (s.f.) along almost the entire length. The highest Ic recorded 608 A/cm-width with the Jc value of 2.43 Ma/hboxcm2. Furthermore, a new IBAD-MgO deposition method was developed, using DC-reactive sputtering which is expected to be inexpensive and easy to scale up. This system brought about a high production rate of 150 m/h in spite of the small deposition area (6 times 20 cm2). The GdBCO on this buffered substrate also showed a high Ic value of 286 A/cm-width at 77 K and s.f., corresponding to the Jc value of 1.43 Ma/hboxcm2.

Transmission electron microscope study on electrodeposited Gd2O3 and Gd2Zr2O7 buffer layers for YBa2Cu3O7−δ superconductors

We have investigated the microstructures of electrodeposited Gd2O3 (GO) and Gd2Zr2O7 (GZO) buffer layers for YBa2Cu3O7−δ (YBCO) superconductors with conventional transmission electron microscopy (TEM). A high density of nanoscale voids was present in the GZO buffer layers. No voids were observed in GO buffer layers grown on GZO. YBCO superconductor grown on the GO/GZO buffer layer structure produced a critical current density (Jc) of 3.3×106A/cm2 at 77K in zero field.

Rapid Formation of 200 m-long YBCO Coated Conductor by Multi-Stage CVD

Toward the industrialization of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) coated conductors for practical applications, metal-organic chemical vapor deposition (MOCVD) has been investigated. We applied multi-stage MOCVD to achieve high-speed production of coated conductor because the increase of the number of depositing stages placed in a line could enlarge deposition area. Using 12-stage CVD, we succeeded in deposition of highly biaxially oriented YBCO layer at tape transfer speed of 50 m/h on the CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> capped ion-beam-assisted-deposition (IBAD) - Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (GZO) buffered Hastelloy tape, and achieved high critical current density ( J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) exceeding 2 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in a short sample. And it was found that lowering substrate temperature according to YBCO layer growth was effective to increase I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . Using this method, high critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of 174 A was achieved by 1 mum thick YBCO layer which passed through 12-stage CVD, and 227 A by 1 mum thick YBCO layer deposited by 6-stage one. Based on these results, three 200 m-class YBCO layers were deposited by multiple depositions at tape speed of 50 m/h each, using the 12-stage CVD system. A 203 m-long YBCO layer was successfully deposited with end-to-end I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of 92.8 A, so that the multiplication of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and length reached 18.8 kA ldr m. These results indicate that a multi-stage CVD technique is useful for a rapid fabrication of long YBCO coated conductor.

Study of Compositional and Artificial Pinning Effects on Superconductivity of Pulsed-Laser Deposited Gd-123 Films for Coated Conductor Applications

Critical temperature (Tc), critical current density (Jc) and flux pinning characteristics of superconducting films are crucially influenced by their chemical composition. We studied the effect of small composition variations on superconductivity of GdBa2Cu3O7-x (Gd-123) films grown by pulsed laser deposition (PLD) technique. Several pathways to control the composition of Gd-123 films were studied: variation of clearance between edge of laser plume and substrate surface, utilization of off-stoichiometric target compositions and addition of GdZrO3. Positive effect of Ba-deficiency on superconductivity of Gd-123 films was shown. Comparative study of Gd-123 and Y-123 films on CeO2 capped Gd2Zr2O7 (GZO) buffered Hastelloy tapes confirmed the advantage of Gd-based compositions for application in magnetic fields and their high potential for fabrication of long-length coated conductors.

Development of a thick GdBCO and ZrO2-doped GdBCO film with a high critical current on a PLD-CeO2/IBAD-GZO metal substrate

In order to obtain a high critical current, Ic, we have fabricated a thick GdBa2Cu3O7−x (GdBCO) film by the pulsed laser deposition (PLD) method on a PLD-CeO2/ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate. The film of a 3.6μm thickness exhibited the highest critical current of 522A/cm at self-field and at 77K. It was found that a low volume fraction of a-axis oriented grains was obtained in the thick GdBCO films, compared to YBa2Cu3O7−x (YBCO) films. The GdBCO films showed a higher critical current density (Jc), than YBCO films in all thicknesses from 0.2 to 3.6μm. Furthermore, we have improved Ic in a magnetic field by the introduction of artificial pinning centers using a 5mol% ZrO2-doped GdBCO target. In the measurement of angular dependence of Ic, which was much improved at 0°, the magnetic field was parallel to the c-axis. The Ic value at 3T was 59.5A/cm at 0° and showed a minimum of 42.3A/cm at 82° for the film of a 2.3μm thickness. The minimum value at 3T in angular dependence of Ic was about five times higher than that of the YBCO film and two times higher than that of pure the GdBCO film.

Effect of substrate roughness on IBAD–GZO template layer

Gd2Zr2O7 (GZO) layers were deposited on rolled, mirror like polished and electropolished Ni-based alloy (Inconel) tapes by the ion-beam-assisted deposition (IBAD) method and were investigated especially in terms of the effect of substrate roughness on the crystal grain alignment. Their surface roughness, Ra, was 7.6–12.3nm, 4.3–4.7nm and 1.4–3.4nm, respectively. The deposition time was varied from 1h to 6h. Crystalline alignment of these films was observed by X-ray diffraction (XRD) and cross-sectional transmission electron microscope (TEM). The grain alignment of the IBAD–GZO was improved by using flat surfaces. GZO film on the electropolished substrate got to align from closer point near the interface than that on rolled substrates.

Investigation of thick PLD-GdBCO andZrO2 doped GdBCO coated conductors with high critical current onPLD-CeO2 capped IBAD-GZO substrate tapes

In order to increase the critical current,Ic, we havefabricated thick GdBa2Cu3O7−δ (GdBCO) coated conductors (CCs) by the pulsed laser deposition (PLD) method onPLD-CeO2/ion-beam assisteddeposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate tapes. The highest critical current value was522 A cm−1 for athickness of 3.6 µm in self-field at 77 K. It was found that a low volume fraction ofa-axis orientated grains was obtained in the thick GdBCO CCs, compared toYBa2Cu3O7−δ (YBCO) CCs. Consequently, the GdBCO CCs showed higher critical current density(Jc) than YBCO CCs in all thicknesses from 0.2 to3.6 µm. Furthermore, we have succeeded in improvingIc in a magnetic field by the introduction of artificial pinning centres using a 5 mol%ZrO2 doped GdBCO target. In the measurement of theIc dependence on themagnetic field angle, θ,Ic was much improved,especially at 0°, i.e., with the magnetic field parallel to thec-axis. TheIc value at3 T was 59.5 A cm−1 at0° and it showeda minimum of 42.3 A cm−1 at 82° for 2.28 µm thick CC. The minimum value in the angular dependence ofIc at 3 T was about five times higher than that of YBCO CC and two times higher than thatof pure GdBCO CC.

Investigation of magnetic properties of YBCO film with artificial pinning centers on PLD/IBAD metal substrate

In order to improve the critical current density (Jc) in magnetic fields, we have fabricated YBa2Cu3O7−x (YBCO) coated conductors with artificial pinning centers by pulsed laser deposition (PLD) method on a Hastelloy™ tape buffered by a self epitaxial PLD-CeO2 layer and an ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO) layer. Artificial pinning centers were introduced by the PLD deposition using YBCO target including YSZ particles. The Jc value was improved and abnormal microstructure was found to be effective for pinning. We call this new nano-epitaxial BaZrO3/YBCO structure “the bamboo structure” from its anisotropic growth and morphology. Furthermore, for the 1.16μm in thickness, Ic showed high value of 40.7A at 77K and 3T parallel to the c-axis. Namely, “the bamboo structure” also contribute to strong pinning in magnetic fields parallel to the c-axis in the film as thick as 1.16μm.

Assessment of Chemical Solution Synthesis and Properties of Gd2Zr2O7 Thin Films as Buffer Layers for Second-Generation High-Temperature Superconductor Wires

Chemical solution processing of Gd2Zr2O7 (GZO) thin films via sol-gel and metalorganic decomposition (MOD) precursor routes have been studied on textured Ni-based tape substrates. Even though films processed by both techniques showed similar property characteristics, the MOD-derived samples developed a high degree of texture alignment at significantly lower temperatures. Both precursor chemistries resulted in exceptionally dense, pore-free, and smooth microstructures, reflected in the cross-sectional and plan-view high-resolution scanning and transmission electron microscopy studies. On the MOD GZO buffered Ni–3at.% W (Ni–W) substrates with additional CeO2/YSZ sputtered over layers, a 0.8-μm-thick YBa2Cu3O7−δ (YBCO) film, grown by an ex situ metalorganic trifluoroacetate precursor method, yielded critical current, Ic (77 K, self-field), of 100 A/cm width. Furthermore, using pulsed-laser deposited YBCO films, a zero-field superconducting critical current density, Jc (77 K), of 1 × 106 A/cm2 was demonstrated on an all-solution, simplified CeO2(MOD)/GZO(MOD)/Ni–W architecture. The present study establishes GZO buffers as a candidate material for low-cost, all-solution coated conductor fabrication.

The influence of assisting ion elements on texture improvement of IBAD-Gd2Zr2O7 films

The texture evolution property of Gd2Zr2O7 (GZO) template films on non-textured Ni-based alloy was studied by off-normal ion-beam-assisted deposition (IBAD) at low temperature of 200°C, with varied bombarding ion elements of Ar, Ne, and O. In all cases a 〈111〉 axis aligned toward the ion incident direction preserving out-of-plane (100) alignment. The in-plane mosaic spread (Δϕ) were clearly deteriorated for GZO films formed with assisting ions of Ar+Ne mixture or pure oxygen, compared to the case for pure Ar ion assisting. On the other hand, no recognizable ion elemental dependence on Δϕ was observed when GZO films were homoepitaxially grown by IBAD on already textured GZO surface.

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

We prepared GdBa2Cu3O7−δ (Gd-123) coated conductors by the pulsed laser deposition (PLD) method onPLD-CeO2/ion-beam assisteddeposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate tapes. The Gd-123 film showed a higher critical current density(Jc) in magneticfields (B) and highercritical temperature (Tc) than those of YBa2Cu3O7−δ (Y-123) film. The Gd-123 film exhibited a highJc valueof 0.19 MA cm−2 at 3 T () in liquid nitrogen (77 K), and theTc value was93.8 K. The Jc value at 3 T was twice as high as that of Y-123 film. Moreover, the angular dependence in magnetic fieldsof Jc for Gd-123 was also superior to that of Y-123. The reduction ofJc by the magnetic field angle for Gd-123 was less sensitive thanthat in Y-123. Furthermore, Gd-123 clearly exhibited a peak at0° () as well as at 90° () in the relationship of Jc on themagnetic field angle curve (Jc–θ), while Y-123had no peak at 0°. These superior characteristics are considered to be due to the existingdefects, such as stacking faults, as observed by transmission electronmicroscopy. PLD-Gd-123 coated conductors, with pinning-effective defects, highJc and lowanisotropy in Jc–θ, show promise for future applications.

Magnetic Field Dependence of Critical Current Density of PLD RE-Ba-Cu-O (RE=Gd, Sm, Dy, Er, Y) Film on CeO2 Capped IBAD-GZO Layers

AbstractWe prepared REBa2Cu3O7- δ (RE= Gd, Sm, Dy, Er, Y) coated conductors on pulsed laser deposition (PLD) -CeO2/ion-beam assisted deposition (IBAD) – Gd2Zr2O7 (GZO) / metal tapes by the PLD method and measured the characteristics in magnetic fields. The GdBa2Cu3O7- σ (Gd-123) films showed superior characteristics than others in magnetic fields and showed weak anisotropy. Critical current density (Jc) value of the Gd-123 film was 3.87MA/cm2 at self-field and 0.19MA/cm2 at 3 T of perpendicular field to the tape surface in liquid nitrogen (77 K). Angular dependences in magnetic fields (Jc -Θ) of the Gd-123 and the SmBa2Cu3O7- σ (Sm-123) were superior to others and peaks in Jc -Θ were found also at 0 degree. The reduction ratios of Jc in Jc -Θ for the Gd-123 film and the Sm-123 film were smaller than other films. Transmission electron microscopy showed that the Gd-123 film had many stacking faults. It may be considered that this stacking faults naturally introduced by the PLD method contribute to improvement of anisotropy of Jc -Θ in the Gd-123 film.

マルチプルーム&amp;bull;マルチターンPLD法による高&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; YBCO長尺線材

We have investigated YBa2Cu3O7-X (YBCO) coated conductor fabricated using a multi-plume and multi-turn (MPMT) pulsed-laser deposition (PLD) method. MPMT-PLD has been improved to a technique that enables the fast deposition of high critical current (Ic) YBCO layer for a long coated conductor fabrication. We used a substrate that a CeO2 cap layer deposited by PLD method on a Gd2Zr2O7 (GZO) buffered Hastelloy tape using the ion-beam assisted deposition (IBAD) method. The YBCO layer was deposited using MPMT-PLD and reel-to-reel tape transfer system. We attained the highest Ic of 313 A at a tape speed of 3.33 m/h using the MPMT-PLD method on a short sample. Then, we successfully deposited a 212.6 m-long YBCO layer at a tape speed of 3.75 m/h using the MPMT-PLD method. This YBCO coated conductor had a high Ic as high as 245 A, and the multiplication of Ic and length exhibited a high value of 52,087 A·m.

The visualization of current-limiting defects inYBa2Cu3O7 films on ion-beam assisted deposition buffer layers of yttrium-stabilizedZrO2 and Gd2Zr2O7

For the production of high-current-carrying, long-length superconducting wires or tapes, itis necessary to use biaxially textured metallic substrates or buffer layers. Thoughbeing highly textured, the deposited superconducting film exhibits a complexdefect structure which (locally) suppresses the critical current and alternatescharacteristically the magnetic flux distribution seen in magneto-optical imaging.In this paper, we report on pulsed laser deposited YBaCuO films on biaxially textured yttrium-stabilizedZrO2 (YSZ)and Gd2Zr2O7 (GZO) buffers which were grown by ion beam assisted deposition (IBAD) on polycrystallinesubstrates. The current-limiting defect structure turns out to resemble closely acombination of a dense distribution of pinhole-like induced growth distortions and a finegrain boundary network. The current suppression is caused on the one hand by the densepacking of pinhole-like defects. On the other hand, we observe a substantial currentanisotropy being related to the surface morphology of the buffer layers and the direction ofthe IBAD-beam.

Investigation of high JcY Ba2Cu3O7−x coated conductors prepared by pulsed laser deposition on self-epitaxial CeO2 buffers

For Y Ba2Cu3O7−x (YBCO) coatedconductors with high Jc, we have been investigating pulsed laser deposition (PLD) processing using the ‘self-epitaxial’PLD-CeO2 layer on an ion beamassisted deposition (IBAD)-Gd2Zr2O7 (GZO) buffered Hastelloy tape. In this study using short samplesof 10 mm in length by 10 mm in width, a high critical current density,Jc, valueof 4.4 MA cm−2 was obtained for a substrate with the delta phi value of2.4°. We also confirmed the relationship that theJc value of YBCO increased exponentially with decreasing in-plane grainalignment of YBCO. Furthermore, we also succeeded in deposition of a highJc and thick YBCO film;the thickness was 1.2 µm and the Jc value was2.3 MA cm−2. This valuecorresponds to 276 A/cm-width. Based on these results, a metre long YBCO coated conductor was fabricated using a reel-to-reel system.Consequently, Jc of 1 MA cm−2 was obtained for a long coated conductor. Now, work is in progress to fabricatea longer and thicker YBCO coated conductor with high critical current,Ic.

ＩＢＡＤ‐ＰＬＤ法による長尺ＹＢＣＯ線材の開発 ＩＢＡＤ法を用いたＧｄ２Ｚｒ２０７二軸配向長尺基板の作製

We developed biaxially textured Gd2Zr2O7 (GZO) templates by ion-beam assisted deposition (IBAD) for YBa2Cu3O7−δ high temperature superconducting wires. Since “assisting” ions bombard the surface of a film concurrently during deposition, the growth mechanism becomes rather more complicated than the ordinary sputtering method with a single ion beam. Based on the result of investigations about a correlation between the conditions of ion beams and the properties of films, we successfully fabricated a 105 m long IBAD-GZO tape with full width at half maximum of 15 degrees in X-ray φ-scan measurement.