High-temperature Superconducting Layer Research Articles

Mechanism of critical current suppression in high-temperature superconductors with increasing concentration of defects

Possible mechanisms of the decrease in the critical current density jc with increasing defect concentration have been considered on the basis of calculations of jc in a model system imitating a high-temperature superconducting layer. It is concluded that the main mechanism of the decrease in the critical current is the reduction of the effective pinning potential caused by the increase in the defect concentration.

An approach for electrical self-stabilization of high-temperature superconducting wires for power applications

Electrical and thermal stability of high-temperature superconducting (HTS) wires∕tapes are essential in applications involving efficient production, distribution, and storage of electrical energy. We have developed a conductive buffer layer structure composed of bilayer La0.7Sr0.3MnO3∕Ir on a textured Ni–W alloy metal tape to functionally shunt the HTS layer to the underlying substrate. The key feature is the Ir layer, which serves as a barrier to both inward diffusion of oxygen and outward diffusion of metal substrate cations during fabrication. Electrical and microstructural property characterizations of YBa2Cu3O7-δ films on short prototype conductors demonstrate self-field critical current density values, Jc, exceeding 2×106A∕cm2 at 77K and excellent electrical coupling to the underlying metal substrate, with no unwanted insulating oxide interfaces. Implementing this approach in power technologies would significantly increase the engineering current density of the conductor and reduce overall process costs.

The role of dynamic SIMS in process development for high-temperature superconducting wire

Flexible metal substrates for long-length high-temperature superconducting (HTS) wires, typically Ni or Ni-alloy foils, include single or multiple buffer layer coatings to provide chemical barriers for the active HTS layer. Chemical issues abound in these multilayer structures, including both intended and unintended bulk reactions, interlayer reactions (corrosion, interlayer compounds), and interlayer diffusion. These effects are a consequence of subjecting multilayer metal/dielectric structures to the rigors of vacuum processing and ex situ conversion reactions. Data are presented that show the applicability of dynamic SIMS (quadrupole, Cs +) in the development of chemically robust structures for HTS applications.

The role of dynamic SIMS in process development for high-temperature superconducting wire

Flexible metal substrates for long-length high-temperature superconducting (HTS) wires, typically Ni or Ni-alloy foils, include single or multiple buffer layer coatings to provide chemical barriers for the active HTS layer. Chemical issues abound in these multilayer structures, including both intended and unintended bulk reactions, interlayer reactions (corrosion, interlayer compounds), and interlayer diffusion. These effects are a consequence of subjecting multilayer metal/dielectric structures to the rigors of vacuum processing and ex situ conversion reactions. Data are presented that show the applicability of dynamic SIMS (quadrupole, Cs + ) in the development of chemically robust structures for HTS applications.

Vapour pressure and heat capacities of metal organic precursors, Y(thd) 3 and Zr(thd) 4

The vapour pressure of two metal organic precursors, Y(thd) 3 [CAS RN: 15632-39-0] and Zr(thd) 4 [CAS RN: 18865-74-2] (thd=2,2,6,6-tetramethylheptane-3,5-dionate), used for metal organic chemical vapour deposition of high-temperature superconductor layers, was measured by a static method in the technologically important temperature range from 395 to 465 K. The experimental data were fitted by simple two-parameter equation and represent updated values of the present day high-purity materials providing comparison with the previously published data. Heat capacities in the temperature range from 308 to 565 K are also reported.

Electrical and magnetic properties of conductive Cu-based coated conductors

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.

Microscopic Studies of the Crystalline Structure of Ferroelectric and High Temperature Superconductor Layers

Properties of ferroelectric ceramics and superconductors essentially depend on the microstructure formed during thermal processing of the material. Active electronic materials synthesized from oxides and carbonates by solid state reaction, and ceramic samples produced by conventional technology were studied. Thick layers have been sedimented on ceramics and single crystal substrates and fired in accordance with melt textured growth (MTG) technology. Choice of the substrate--its lattice parameters and structure--is essential. The surface morphology and structure of high temperature superconductor layers prepared on passive substrates of different crystal structures were studied by scanning electron microscopy. The effect of substrate material on the structure formation of the layers is discussed.

Modeling the passive microwave devices based on planar multilayer anisotropic structures with high-temperature superconductors

The electrodynamic properties of an arbitrary multilayer medium, including anisotropic layers and conductors of an arbitrary shape on one of the interfaces, are studied. The conductors represent thin layers of a high-temperature superconductor (HTSC). A system of integral equations for the electric field is solved in the spatial domain. The electrodynamic problem was solved by numerical methods to determine the surface current density by applying the Galerkin procedure and by solving the main matrix equation relative to coefficients of the current density expansion in a basis set of finite functions. The losses in HTSC layers are taken into account by using the concept of the equivalent surface impedance and the Leontovich boundary conditions. The anisotropy is taken into account in determining the Green dyad for a structure with an arbitrary number of anisotropic or isotropic layers. Correctness of the proposed model is confirmed by the results of calculations of the surface current density distribution.

Measuring the current distribution in a 10 m long high temperature superconducting cable conductor

To obtain realistic data on high temperature superconducting (HTS) conductors, a 10 m long cable conductor was built using 193 HTS tapes placed in eight concentric layers. To fully exploit the current carrying capability of all the HTS tapes and to minimise the AC losses the conductor was designed to have an almost even current distribution with respect to the HTS tapes. The outer diameter of the former was 35 mm and the outer diameter of the conductor was about 40 mm. A thin layer of electrically insulating Mylar TM foil was wound between each HTS layer. This way, the current in one particular layer may be treated as a tubular current sheet. The current in each layer was determined using custom made flat Rogowski coils placed between the superconducting layers. For this conductor, each layer was carrying <25% of the total load current.

Growth and characterization of conductive SrRuO3 and LaNiO3 multilayers on textured Ni tapes for high-Jc Yba2Cu3O7–delta; coated conductors

Power applications of high-temperature superconducting (HTS) coated conductors will require stabilization against thermal runaway. We have developed conductive buffer layers to electrically couple the HTS layer to the underlying metal substrate. The structure comprises the layer sequence of SrRuO3 (SRO) on LaNiO3 (LNO) on biaxially textured Ni substrates. We report baseline investigations of compatibility of SRO/LNO multilayer structure with processing of Yba2Cu3O7−δ (YBCO) and demonstrate biaxially textured YBCO films on conductively buffered Ni tapes. These YBCO coatings exhibit self-field Jc values as high as 1.3 × 106 A/cm2 at 77 K, and the entire structure (HTS + conductive buffers + metal substrate) shows good electrical connectivity. These results demonstrate that SRO/LNO buffer layers may provide a basis for stabilized coated conductors.

An artificially anisotropic thermoelectric material with semiconducting and superconducting layers

The thermoelectric parameters of an artificially anisotropic material composed of semiconducting and superconducting layers are considered. The transverse thermoelectric figure of merit and the sensitivity of a sensor responding to small heat fluxes are calculated. The use of high-temperature superconductor layers appreciably changes the optimal geometry of the layered structure (layer inclination angle and thickness ratio) compared with normal conductors. The figure of merit and the sensitivity of a thermoelectric element with superconducting layers exceed the respective parameters of a structure with metallic layers by a factor of 2–3.

Interaction of a surface magnetostatic wave with an inhomogeneous granular HTSC medium

In the present paper the dispersion properties of surface magnetostatic waves (SMSWs) propagating in a stratified structure, ferrite film—high-temperature superconducting layer, have been investigated. The problem of SMSW propagation in an inhomogeneous stratified medium has been solved and the dispersion equation has been obtained. In the solution of this problem, the granular nature of the high-temperature superconducting (HTSC) medium and the exposure to a constant magnetization field have been taken into account. Upon exposure to the constant magnetic field the HTSC film becomes an inhomogeneous anisotropic medium with respect to a variable magnetic field. The nonhomogeneous wave equation describing the SMSW field in a granular HTSC medium has been solved by the method of sequential iterations. Corrections for the SMSW velocity and attenuation, calculated with the use of the exact dispersion equation, are significant in comparison with previously obtained approximate values and exceed 20 and 40%, respectively. The method of analyzing electromagnetic fields in inhomogeneous granular high-temperature media can be used to solve some other problems, where spatially inhomogeneous HTSC media are used.

Tunneling in HTS junctions

The effects caused by the layered structure of high-temperature superconductors (HTS) ought to be taken into consideration at the time of constructing different HTS junction devices. The authors demonstrate this by studying tunneling phenomena in HTS. The tunneling current-voltage characteristics of different structures such as Normal Metal-Insulator-HTS (NIS-structure) and HTS-Insulator-HTS (SIS-structure) are calculated. The real layered structure of HSS is taken into account and corresponding peculiarities on I(V) are obtained. The authors have analyzed different types of contacts which are realized in the NIS- and SIS-junctions. The contributions of the superconducting and normal layers of HTS to the tunneling current of NIS- and SIS-structures are found.

Crystal Growth and Crystalline Layers of High Temperature Superconductors: Characterization and Application

Crystal Research and TechnologyVolume 32, Issue 1 p. 7-33 Review Crystal Growth and Crystalline Layers of High Temperature Superconductors: Characterization and Application† Prof. Dr. Peter Görnert, Prof. Dr. Peter Görnert Institut für Physikslische Hochtechnologie e.V., Helmholtzweg 4, 507702 Jena, P.O. Box 100 239, GermanySearch for more papers by this author Prof. Dr. Peter Görnert, Prof. Dr. Peter Görnert Institut für Physikslische Hochtechnologie e.V., Helmholtzweg 4, 507702 Jena, P.O. Box 100 239, GermanySearch for more papers by this author First published: 19 February 2006 https://doi.org/10.1002/crat.2170320103Citations: 11 † Dedicated to Professor Dr. Hermann Neels on the occasion of the 3th anniversary of his Editorship of Crystal Research and Technology AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume32, Issue11997Pages 7-33 RelatedInformation

Josephson plasma resonance in the vortex state of high temperature superconductors

We study the microwave response perpendicular to the superconducting layers of high temperature superconductors in a wide range of temperatures and fields. A novel microwave response,i.e. Josephson plasma resonance, shows up in the superconducting state of Bi2Sr2CaCu2O8+δ. This resonance enable us to measure the magnitude of interlayer phase coherence quantitatively. Josephson plasmon is shown to interact strongly with the vortices. Therefore it provides a new powerful tool to probe the vortex state. The vortex state of high temperature superconductors is discussed in the light of the interlayer phase coherence.

Normal metal, ohmic contacts to high-temperature superconducting YBa 2Cu 3O 7-δ thin films suitable for multichip modules

Normal metal, ohmic contacts to high-temperature superconductor (HTSC) materials will be used to form via structures between HTSC interconnect levels, and also, substrate bonding pads in a superconducting multichip module (SMCM). Specific contact resistivities below 10 −8 Ω cm 2 will be required for such contacts to control signal attenuation and local contact heating of the LN 2cooled SMCM. Previous work on normal metal/superconducting contacts has not focused on metallization schemes which will be stable during subsequent high-temperature processing. Metal contacts of gold, silver, and palladium were formed on superconducting thin films of YBa 2Cu 3O 7-δ via evaporation and sputtering through a shadow mask followed by annealing in various ambients and at several temperatures. Palladium contacts oxidized readily during anneal, and sputtered gold contacts required additional processing and exhibited higher specific contact resistivities. The best contacts were obtained by a controlled-cooling oxygen anneal of evaporated gold or silver, as indicated by normal-state specific contact resistivities of 3 × 10 −5 Ω cm 2 and 4 × 10 −5 Ω cm 2 , respectively. This work differs from previously published results by describing contacts which required no extensive preparation of the HTSC surface and were stable to 700 °C, indicating these contacts would be compatible with subsequent high-temperature processing of the additional HTSC layers required in a multi-level SMCM.

Dispersion of magnetostatic surface waves in ferrite-htsc structures near the phase transition

We present a detailed study of the dispersion properties of surface magnetostatic waves in layered structures of ferrite and high temperature superconductor (HTSC) layers. We solve the propagation problem for the surface magnetostatic waves under a quasistatic approximation, and obtain the dispersion relation. We present an analysis of this dispersion near the phase transition temperature in the HTSC layer. The calculations show that when the HTSC material transforms to the superconducting state the dispersion properties of the magnetostatic waves changes suddenly: the damping decreases by 4–10 dB and the phase velocity increases by a factor of 2–4. These results support experiments which have been performed, in which surface magnetostatic waves have been studied in a YIG film with gallium impurities and a YBaCuO film on a lithium niobate substrate.

Flux penetration and pinning in superconductor-ferromagnet superlattices

Flux penetration in superconductor-ferromagnet superlattices is studied theoretically. The parallel lower critical field is calculated and the characteristic temperature and layer thickness dependence is discussed. It is found that strong flux pinning and high critical current densities are obtained for superlattices with thin ferromagnetic and thick high-temperature superconducting layers.

Temperature Dependent Growth of LaAIO3 Films on YBa2Cu3O7 C-Axis Films for Multilayer Structures

AbstractFabrication of ultra smooth films, free of micro-shorts, is essential to the development of High Temperature Superconducting (HTS) thin film devices. One such example is a SNS junction consisting of two HTS layers separated by a uniformly smooth continuous barrier material. Other schemes under consideration require multilayer structures of up to 5 - 7 epitaxially grown layers of complex oxide material. Successful fabrication of such devices necessitates understanding the epitaxial growth of polycrystalline oxide films on polycrystalline film templates. Toward this end we have developed a set of deposition parameters that produce high quality epitaxial insulating layers suitable for HTS device applications. All films in this study were grown by off-axis RF magnetron sputter deposition. LaAlO3 films were deposited over MgO grown YBa2Cu3O7 (YBCO) c-axis thin films at temperatures ranging from 200 to 700C and on virgin substrates at 600C. Atomic Force Microscopy, eddy current measurements, and x-ray diffraction techniques were used to monitor the effect of growth conditions on the resulting film crystallinity, nanostructure, and electrical properties.Ex-situ interrupted growth characterization of these materials has yielded new insight into the processes that control the growth mechanism and resulting microstructure. All films were polycrystalline. Below 600C, LaAlO3 films were not epitaxial while films grown at 650C showed some &lt;200&gt; orientation. The shape of the underlying YBCO film is most clearly evident for the film grown at 400C. Surface roughness depended on the appearance of crystals on the film surface. The superconducting properties of the underlying YBCO film required O2 annealing prior to deposition of the LaAlO3 layer.

Effects of cold rolling and thermal annealing on superconducting properties of 2212 Bi-Sr-Ca-Cu-O/Ag tapes

High-temperature superconducting (HTS) tapes were fabricated by doctor-blade coating of a BSCCO 2212 dispersion in Butvar-B76 binder, and thermal processing in a three-zone belt furnace. The crystalline properties of these HTS layers were studied by X-ray diffraction techniques. The superconducting properties of HTS tape conductors were examined using AC susceptometry. The effects of sintering, cold rolling, and thermal annealing were monitored by following the temperature dependence of the AC susceptibility and process-induced changes in the crystalline microstructure. A significant degradation of the superconducting properties due to cold rolling has been observed. This degradation is attributed to inferior intergranular coupling and appears to be reversible. Thermal annealing of the cold-rolled samples leads to the full recovery of the AC susceptibility versus temperature response.