Showing papers by "David K. Christen published in 2003"
TL;DR: In this article, a 1.65-μm-thick YBCO film with a critical current density of 1.4 x 10 6 A/cm 2 in self field at 75 K was achieved on sputtered LaMnO 3 -buffered IBAD MgO substrates.
Abstract: A single LaMnO 3 buffer layer was developed for the growth of superconducting thick YBa 2 Cu 3 O 7 - δ (YBCO) films on polycrystalline Ni-alloy substrates where a biaxially textured MgO layer, produced by ion-beam assisted deposition (IBAD), was used as a template. Using pulsed laser deposition, a 1.65-μm-thick YBCO film with a critical current density of 1.4 x 10 6 A/cm 2 in self field at 75 K was achieved on sputtered LaMnO 3 -buffered IBAD MgO substrates. This corresponds to a critical current (I c ) of 231 A/cm-width. This result demonstrates the possibility of using both LaMnO 3 buffer and IBAD MgO template for producing high current density YBCO-coated conductors.
41 citations
TL;DR: In this paper, a conductive buffer layer architecture on biaxially textured nonmagnetic Cu tapes was proposed to electrically couple the HTS layer to the underlying metal substrate.
Abstract: The development of YBa2Cu3O7−δ (YBCO)-based coated conductors for electric power applications will require electrical and thermal stabilization of the high-temperature superconducting (HTS) coating. In addition, nonmagnetic tape substrates are an important factor in order to reduce the ferromagnetic hysteresis energy loss in ac applications. We report progress toward a conductive buffer layer architecture on biaxially textured nonmagnetic Cu tapes to electrically couple the HTS layer to the underlying metal substrate. A protective Ni overlayer, followed by a single buffer layer of La0.7Sr0.3MnO3, was employed to avoid Cu diffusion and to improve oxidation resistance of the substrate. Property characterizations of YBCO films on short prototype samples revealed self-field critical current density (Jc) values exceeding 2×106 A/cm2 at 77 K and good electrical connectivity. Magnetic hysteretic loss due to Ni overlayer was also investigated.
34 citations
TL;DR: In this paper, YBCO films with a thickness of 0.9 μm have been deposited by ex situ conversion of a trifluoroacetate-based metal organic decomposition precursor on both RABiTS TM (NiW) and MgO-IBAD Hastelloy substrates.
Abstract: Epitaxial YBCO films with a thickness of 0.9 μm have been deposited by ex situ conversion of a trifluoroacetate-based metal organic decomposition precursor on both RABiTS TM (NiW) and MgO-IBAD Hastelloy substrates. These are potential processes for fabricating second generation coated conductor wires. I c values, at 77 K and self-field, as high as 202 and 194 A/cm-width have been achieved on the RABiTS TM and MgO-IBAD samples, respectively.
29 citations
TL;DR: In this article, a LaMnO/sub 3/buffered ion-beam assisted deposition (IBAD) MgO template layer is used for growing high current density YBCO films.
Abstract: High J/sub c/YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films have been fabricated on LaMnO/sub 3/ buffered ion-beam assisted deposition (IBAD) MgO template layers. A LaMnO/sub 3/ buffer layer is compatible with MgO surfaces and also provides a good template for growing high current density YBCO films. LaMnO/sub 3/ buffer layers were deposited using rf magnetron sputtering. On LaMnO/sub 3/-buffered-MgO [100] single crystal substrates, YBCO films with a J/sub c/ of over 4 M/cm/sup 2/ were grown using both pulsed laser deposition (PLD) and ex-situ BaF/sub 2/ process. Using PLD, J/sub c/ of 1.8 MA/cm/sup 2/ at 77 K was obtained on 200-nm-thick YBCO films grown on LaMnO/sub 3/-buffered MgO IBAD/Ni-alloy substrates. In addition, an I/sub c/ of 230 A/cm-width was obtained for 1.65-/spl mu/m-thick YBCO films grown on LaMnO/sub 3/-buffered MgO IBAD/Ni-alloy substrates using PLD at Los Alamos National Laboratory. This performance is comparable to the best single-layer results achieved on IBAD-MgO substrates.
28 citations
TL;DR: In this article, high critical current density (high-J c ) YBa 2 Cu 3 O 7 - Φ (YBCO) films were obtained by pulsed laser ablation on biaxially textured Cu substrates.
Abstract: High critical current density (high-J c ) YBa 2 Cu 3 O 7 - Φ (YBCO) films were obtained by pulsed laser ablation on biaxially textured Cu substrates. To achieve epitaxy of LaMnO 3 (LMO) on Cu, thin epitaxial Ni overlayers were deposited on Cu tapes. The structure comprises the layer sequence of YBCO/LMO/Ni/Cu. For 200-nm-thick YBCO, self-field J c values exceeding 1 x 10 6 A/cm 2 at 77 K were achieved. Characterization of these short prototype conductors revealed good structural and morphological properties. Magnetic analysis suggested that hysteretic loss due to the ferromagnetic Ni overlayer is minimal.
24 citations
TL;DR: In this article, a nonvacuum reel-to-reel dip-coating system has been used to continuously fabricate epitaxial buffer layers on mechanically strengthened, biaxially textured Ni-(3 at.% W-1.7 at.%).
Abstract: A nonvacuum reel-to-reel dip-coating system has been used to continuously fabricate epitaxial Gd 2 O 3 buffer layers on mechanically strengthened, biaxially textured Ni-(3 at.% W-1.7 at.% Fe), defined as Ni-alloy, metal tapes. Because of its significance as a seed layer, optimum processing conditions (postannealing speed and temperature) of Gd 2 O 3 buffer layers have been studied. Highly textured films were obtained under reducing (96% Ar + 4% H 2 ) atmosphere at temperatures between 1100° and 1150°C; postannealing speed did not significantly affect the crystalline quality of the Gd 2 O 3 . Scanning electron microscopy revealed a continuous, dense, and crack-free surface morphology for these dip-coated buffers. The Gd 2 O 3 layer thickness led to pronounced differences in the growth characteristics of the subsequent YSZ and CeO 2 layers deposited by rf-magnetron sputtering. Epitaxial YBCO films grown by pulsed laser deposition on the short prototype CeO 2 /YSZ/Gd 2 O 3 /Ni-(3 at.% W-1.7 at.% Fe) conductors yielded self-field critical current densities (J c ) as high as 1.2 x 10 6 A/cm 2 at 77 K. Pure Ni tapes were used to assess the viability of dip-coated buffers for long length coated conductor fabrication. The YBCO films, grown on 80 cm long and 1 cm wide CeO 2 /YSZ/Gd 2 O 3 buffered Ni tapes by the industrially scalable ex situ BaF 2 precursor process, exhibited end-to-end self-field J c values of 6.25 x 10 5 A/cm 2 at 77 K. These results demonstrate the reproducible epitaxy of solution-derived seed layers on pure Ni and Ni-alloy tapes as well as underscore the viability of solution approaches for the production of long length YBCO-based coated conductors.
23 citations
TL;DR: In this article, it was shown that the epitaxial growth of commonly used seed layers on textured Ni is mediated by a sulfur superstructure present on the metal surface, and the structural defects generated during seed layer growth (secondary orientations, inplane rotation, incomplete cube texture) can be related to the surface concentration and superstructure coverage.
Abstract: The current carrying capabilities of RABiTS are connected to the crystalline quality of the seed buffer layer and the stability of the metal/seed layer interface. Our study shows that the epitaxial growth of commonly used seed layers on textured Ni is mediated by a sulfur superstructure present on the metal surface. Many structural defects generated during seed layer growth (secondary orientations, in-plane rotation, incomplete cube texture) can be related to the S surface concentration and superstructure coverage. More generally, our results indicate that the epitaxial deposition of several classes of oxides (fluorite, perovskite, RE/sub 2/O/sub 3/) on several {100} fcc metals depends, in addition to chemical stability and lattice match, on the existence and optimization of S superstructures on the metal surface. On these bases, we discuss issues related to the growth of different oxides on Ni, Ni-alloys, and Pd surfaces having different chemical and structural properties.
22 citations
TL;DR: In this article, a buffer layer architecture consisting of LaMnO3/MgO/TiN is proposed as a suitable structural and chemical template for the epitaxial growth of high-transition temperature (Tc) superconductors on Cu metal surfaces.
Abstract: In this paper a novel buffer layer architecture consisting of LaMnO3/MgO/TiN is proposed as a suitable structural and chemical template for the epitaxial growth of high-transition temperature (Tc) superconductors on Cu metal surfaces. Using techniques such as high-energy electron diffraction and scanning transmission electron microscopy, we present in situ and ex situ analyses of the buffer-layer and superconductor growth with focus on structural properties of the interfaces formed. While MgO is a good barrier to oxygen diffusion, we find that MgO alone is not a suitable buffer layer due to rapid Cu diffusion. Further, growth of MgO with a single epitaxy can be hindered by the presence of impurities such as S, which form strongly bonded superstructures on the metal surface. With the addition of a TiN layer as a barrier to Cu diffusion, oxide formation is suppressed, interfaces are clean, and a single cube-on-cube epitaxy is observed. While the Cu/TiN and TiN/MgO interfaces are rough, the MgO and LaMnO3 layers planarize the material, leading to growth of smooth YBa2Cu3O7−δ (YBCO). Residual strain in the YBCO film is 0.25% or less and does not lead to apparent cracking. The superconducting properties of the samples were investigated by electrical transport and magnetization measurements. For the first time, high critical current density (Jc) values are reported for YBCO films grown on (001) single-crystal and 100‹100›?textured Cu surfaces without intervening metal coatings. Jc on single crystal-like substrates is as high as 3.5 MA/cm2. Reduced Jc of approximately 1 MA/cm2 on rolled Cu tapes is limited by damage to the tape surface during the rolling process.
22 citations
TL;DR: In this paper, the transport and structural properties of (La,Sr)TiO3 epitaxial thin films grown by pulsed-laser deposition are investigated and shown to be a viable candidate as a conducting buffer for superconducting film growth on biaxially textured metal tapes.
Abstract: The transport and structural properties of (La,Sr)TiO3 epitaxial thin films grown by pulsed-laser deposition is presented. In particular, the potential use of (La,Sr)TiO3 as a conductive buffer layer for subsequent growth of high temperature superconducting films for coated conductors is discussed. Van der Pauw measurements of film resistivity as a function oxidation conditions show that, for undoped LaTiO3 films, the resistivity increases rapidly as background oxygen pressure is increased, which is consistent with the formation of the LaTiO3þx phase. Sr doping of LaTiO3 significantly enhances the conductivity of thin film materials when synthesized under oxidizing conditions. The transport behavior for Sr-doped LaTiO3 films correlates with structural data showing no significant shift in lattice spacing as oxygen partial pressure is increased during film growth. In addition, the epitaxial growth of (La,Sr)TiO3 on biaxially textured Ni alloy tapes is demonstrated. These results suggest that (La,Sr)TiO3 is a viable candidate as a conducting buffer for superconducting film growth on biaxially textured metal tapes. � 2003 Elsevier Ltd. All rights reserved.
20 citations
TL;DR: In this paper, the structure and transport properties of LaTiO3+x epitaxial thin films grown on (001) SrTiO 3 by pulsedlaser deposition is examined.
Abstract: The structure and transport properties of LaTiO3+x epitaxial thin films grown on (001) SrTiO3 by pulsedlaser deposition is examined. Four-circle X-ray diffraction indicates that the films possess the defect perovskite LaTiO3 structure when deposited in vacuum, with the higher X compounds forming at moderate oxygen pressures. The crystal structure of the LaTiO3 films is tetragonal in the epitaxial films, in contrast to the orthorhombic structure observed in bulk materials. A domain structure is observed in the films, consisting of LaTiO3 oriented either with the [110] or [001] directions perpendicular to the substrate surface. Z-contrast scanning transmission electron microscopy reveals that this domain structure is not present in the first few unit cells of the film, but emerges approximately 2 – 3 nm from the SrTiO3/LaTiO3 interface. Upon increasing the oxygen pressure during growth, a shift in the lattice d-spacing parallel to the substrate surface is observed, and is consistent with the growth of the La2Ti2O7 phase. However, van der Pauw measurements show that the films with the larger d-spacing remain conductive, albeit with a resistivity that is significantly higher than that for the perovskite LaTiO3 films. The transport behavior suggests that the films grown at higher oxygen pressures are LaTiO3+x with 0.4 < x < 0.5.
19 citations
TL;DR: In this article, a single buffer layer of LaMnO/sub 3/ (LMO) has been epitaxially grown on biaxially textured Ni and Ni-alloy substrates by sputter deposition.
Abstract: Single buffer layer of LaMnO/sub 3/ (LMO) has been epitaxially grown on biaxially textured Ni and Ni-alloy substrates by sputter deposition. The property characterizations revealed that LMO buffers can serve both as a chemical as well as a structural buffer for YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films. Epitaxial YBCO films grown on LMO buffers using pulsed laser deposition (PLD) have self-field critical current densities (J/sub c/) exceeding 1 /spl times/ 10/sup 6/ A/cm/sup 2/ at 77 K. The present results have demonstrated the strong prospect of LMO for the practical development of YBCO coated conductors.
TL;DR: In this article, the peak effect in critical current density was investigated by studying the flux dynamics in the vortex lattice using bulk magnetometry, small-angle neutron scattering, and transport measurements on clean single-crystal samples from the same ingot.
Abstract: The peak effect in critical current density ${J}_{c}$ is investigated by studying the flux dynamics in ${\mathrm{V}}_{3}\mathrm{Si}$ using bulk magnetometry, small-angle neutron scattering, and transport measurements on clean single-crystal samples from the same ingot. For a field-cooled history, well-defined structure in the vortex lattice was found for fields and temperatures (H,T) below the peak-effect line ${H}_{P}(T);$ above this line, the structure disappeared. History-dependent, metastable disorder is found only for (H,T) below ${H}_{P}(T)$ but the vortex system is reproducibly re-ordered either by field cooling or a low-frequency, pulsed ``shaking'' transport current. The latter is shown to attain Bardeen-Stephen flux flow. In addition, flux flow is observed at ${H}_{P}(T)$ at high current levels. The results support the traditional picture of ${H}_{P}(T)$ as an order-disorder transition due to the competition between elasticity and pinning.
TL;DR: In this article, the electrical, magnetic, and structural properties of the vortex lattice (VL) in single crystal V 3 Si were studied by transport, bulk magnetometry and small-angle neutron scattering.
Abstract: Electrical, magnetic, and structural properties of the vortex lattice (VL) in single crystal V 3 Si were studied by transport, bulk magnetometry and small-angle neutron scattering. Studies focused on the ‘peak effect’ in critical current density just below the upper critical field of this weak-pinning system. The overall picture is a slightly disordered VL easily re-ordered by transport-current ‘shaking’ and ultimately softening at the peak effect.
TL;DR: When columnar defects are added to Hg-1223 and Tl-2212 superconductors, their vortex state equilibrium magnetization Meq progressively deviates from the usual London ln(B) dependence and the curves become S-shaped as discussed by the authors.
Abstract: When randomly oriented columnar defects (CDs) are added to Hg-1223 and Tl-2212 superconductors, their vortex state equilibrium magnetization Meq decreases substantially. Meq progressively deviates from the usual London ln(B) dependence and the curves become S-shaped. Vortex-defect interactions quantitatively account for this behavior.