Textured Metal Tapes Research Articles

Influence of High-Temperature Annealing of the Textured Metal Ni–W Substrate on the Structural Properties of Seed Layer in HTS 2G tapes

The surface reconstruction of the textured metal tapes at the temperatures typical for the formation of the seed buffer Y2O3 layer of HTS 2G tapes have been revealed and studied for the first time. The influence of a terrace structure of the substrate surface on the characteristics of the texture of the seed Y2O3 layer has been shown. This effect is critically important to the deposition of buffer layers on the moving tape and allows to expand the temperature range of growth, in which the full inheritance of substrate texture by the seed Y2O3 layer is occurred.

High-performance FeSe0.5Te0.5 thin films fabricated on less-well-textured flexible coated conductor templates

We report on the transport properties of FeSe0.5Te0.5 (FST) thin films fabricated on less-well-textured flexible coated conductor templates with LaMnO3 (LMO) as buffer layers using pulsed laser deposition. The LMO buffer layers exhibit large in-plane misalignment of ∼7.72°, which is unfavorable for cuprate-coated conductors due to the high grain boundaries. The FST thin films show a superconducting transition temperature of 16.8 K, higher than that of bulk materials due to the compressive strain between LMO and FST. Atomic force microscopy observations reveal that island-like features appear at the surfaces of both LMO and FST, confirming the island growth mode. A self-field transport critical-current density of up to 0.43 MA cm−2 at 4.2 K has been observed in FST thin films, which is much higher than that in powder-in-tube processed FST tapes. The films are capable of carrying current densities of over 105 A cm−2 in the whole applied magnetic field up to 9 T, showing great potential for high-field applications. The results indicate that, for FST, highly textured metal tapes are not needed to produce coated conductors with high performance, which is of great advantage over cuprate-coated conductors.

<inline-formula> <tex-math notation="TeX">$\hbox{BaHfO}_{3}$</tex-math> </inline-formula>-Doped Thick <inline-formula> <tex-math notation="TeX">$\hbox{YBa}_{2}\hbox{Cu}_{3}\hbox{O}_{7-\delta} $</tex-math> </inline-formula> Films on Highly Alloyed Textured Ni-W Tapes

YBa 2 Cu 3 O 7-δ (YBCO) films with a thickness of up to 2 μm containing nano-sized BaHfO 3 (BHO) have been grown on biaxially textured metal tapes by pulsed laser deposition. Transmission electron microscopy revealed the inclusion of Y 2 O 3 platelets and rod-like BHO structures. A c-axis oriented growth of the YBCO layer and biaxial oriented incorporation of BHO is confirmed by X-Ray diffraction. BHO expands the c-axis of YBCO, flattens the surface of YBCO and densifies the films. Y 2 O 3 inclusions get smaller and finer distributed, possibly with a positive influence on pinning effects. A superconducting transition temperature T c of about 89 K was determined, decreasing slightly with increasing BHO content. Transport current measurements in the maximum Lorentz force configuration showed an increased irreversibility field H irr and higher pinning force density F p with increasing BHO content in high magnetic fields.

Effect of Substrate Temperature and Dislocation Density on the Epitaxial Growth of YBCO Thin Films on Textured Metal Tapes

Epitaxial YBa2Cu3O7-δ(YBCO) thin films were grown on Y2O3/YSZ/CeO2(YYC) buffered Ni-5at%W substrates by direct-current sputtering,and induced by substrate temperature.X-ray diffraction(XRD) results showed that the substrate temperature strongly influenced the epitaxial growth of YBCO films: the a-axis preferential grains grew at lower substrate temperature,and strictly c-axis epitaxial YBCO films were achieved at higher substrate temperature.The amount of a-axis YBCO component evaluated from the ratio of XRD χ-scan integrated intensity of the a-axis and c-axis for the YBCO(102) plane decreased as the substrate temperature increased.Since the development of the a-axis component can result in high angle grain boundaries,which can degrade the Ic passing through the a–b plane,the microstructure and the critical current density of YBCO thin films were improved as substrate temperature increasing.While the microstructure and the critical current density of YBCO thin films were deteriorated above 780℃ for the baseband oxidation and the interface reaction between the YBCO and the buffer layer.The dislocation density in the YBCO thin films was measured and calculated.The relationship between the dislocation density and critical current density(Jc) was systematically investigated,Jc was much more sensitive to the screw dislocation than to the edge dislocation,which was attributed to the spiral growth mechanism of YBCO thin films.

MOCVD and MOD of YBCO and Buffer Layers on Textured Metal Tapes

Different layer architectures produced by only MOD, only MOCVD and combinations of MOD buffers and MOCVD YBCO are presented. RTR MOCVD-YBCO layers obtained on MOD-CeO2/MOD-LZO/Ni5 at%W tapes demonstrate critical current densities up to 2 MA/cm2 at 77 K. On single LZO (50-100 nm) buffered Ni5 at%W tapes from Nexans Superconductors and on RTR MOCVD buffer layers critical current densities between 0.8 and 1.3 MA/cm are obtained. RTR MOD-LZO layers often show delamination during YBCO deposition. Preannealing treatment before YBCO deposition allows to avoid this. Tapes up to 10 m are produced by combination of MOD-LZO and RTR MOCVD-YBCO.

Transport losses in polygonal assemblies of coated conductors with textured-metal substrate

Transport loss characteristics of polygonal assemblies of coated conductors with textured-metal substrate were studied. Coated conductors using two types of textured-metal tape as their substrate were prepared for the experiments: a Ni alloy substrate and a clad-type substrate with reduced magnetism. First, the transport losses of hexagonal assemblies of coated conductors with non-magnetic substrate were measured where the textured-metal tapes were under-lied or over-lied on the coated conductors to simulate the coated conductors fabricated with these textured-metal substrates. The over-lied Ni alloy tapes affect transport loss characteristics substantially; the over-lied or under-lied clad tapes do not substantially affect them. Next, two types of hexagonal assemblies were made using coated conductors fabricated with the textured-metal substrates: the substrates were placed inside in one of them, and they were placed outside in the other. In case of the coated conductors fabricated with the Ni alloy substrate, the measured transport loss of the latter was much larger than that of the former, because the substrates placed outside were exposed to the magnetic field generated around the assembled coated conductors. The measured transport losses reasonably agree with the numerically-calculated ones. In case of the coated conductors fabricated with the clad substrate, the difference between the transport losses of the two types of the assemblies is much smaller; the influence of the magnetism of the clad substrate on AC losses is reasonably small.

Tensile strengths and Young’s modulus of thin copper and copper-nickel (CuNi44) substrates

Abstract In this paper we report a method to determine tensile strengths and Young’s modulus of cubic biaxial textured metal tapes used as substrate materials for coated conductors (CC). Simplicity, rapidity and reproducibility of the procedure are important for the evaluation of continuous in-house productions. Our approach is based on the EN 10002-1 B tensile test method. A key role for satisfactory results is the sample preparation of 100–250 μm thick tapes, which will be described in detail. Copper (E-Cu57) can be successfully transformed to cubic biaxial textured substrates. Best results were achieved by annealing between 750°C and 850°C in reducing atmosphere. Best FWHM values for the ψ scan are 5.51° and for the ϕ scan are 4.5°. Pole figure analysis verified the sharp {001} texture of the tape. Vickers hardness measurements (HV 0.1) for the cold worked material yielded values of 135 and for the annealed tape, values of 37. The ultimate tensile yield strength Rm of the textured substrate is 150 MPa and thus significantly lower than that for the cold worked material (413 MPa). Cubic biaxial substrates could be manufactured from Isotan CuNi44 (WM49) bars. Best results were achieved by annealing at 1200°C in reducing atmosphere. Pole figure analysis verified the {001} texture with other low intensity texture components. Vickers hardness measurements (HV 0.1) for the cold worked material yielded values of 236 and for the annealed tape values of 92. The ultimate tensile yield strength R m of the textured substrate is 300 MPa and thus significantly lower than that for the cold worked material (723 MPa).

MOCVD of coated conductors with electrically conductive buffer layers and their electrical field

A new MOCVD technique was developed for the deposition of oxides at a controlled low oxygen partial pressure, which enable to coat textured metal tapes with electrical conductive perovskites. In a RTR MOCVD-system metal tapes were coated with electrical conductive (La, Ba)MnO3, (La, Sr)MnO3, (La, Sr, Pb)MnO3 and (La, Ba)2CuO4 buffer layers and YBCO. In the same RTR-system YBCO was deposited on different buffered metal tapes. Computer calculations were used to characterise the behaviour for a weak superconducting part of a CC-tape with a conductive buffer layer system.

Investigation of TiN Seed Layers for RABiTS Architectures With a Single-Crystal-Like Out-of-Plane Texture

Sharpening of the substrate texture is key to obtain critical current densities approaching single crystal values in coated conductors. In particular, great improvements in J/sub c/ are obtained by narrowing the substrate texture down to values of 3-4/spl deg/ for both phi-scan and omega-scan FWHM. The best Ni-alloy substrates used today for RABiTS show FWHM's of 6-5/spl deg/. Although the majority of buffer layers deposited on these tapes by various techniques approximately duplicate the substrate's grain alignment, some materials have been found to develop much sharper out-of-plane texture. Here we report on growth and structural characterization of TiN seed layers on various textured metal tapes. TiN seed layers deposited by PLD have consistently shown tilting of the c-axis toward the direction of the sample's surface normal. We address the extent of such tilt and discuss feasibility of alternative RABiTS architectures that use a TiN seed layer to provide very sharp out-of-plane texture and serve as an effective metal-ion diffusion barrier.

Epitaxial (La,Sr)TiO 3 as a conductive buffer for high temperature superconducting coated conductors

The transport and structural properties of (La,Sr)TiO 3 epitaxial thin films grown by pulsed-laser deposition is presented. In particular, the potential use of (La,Sr)TiO 3 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 LaTiO 3 films, the resistivity increases rapidly as background oxygen pressure is increased, which is consistent with the formation of the LaTiO 3+ x phase. Sr doping of LaTiO 3 significantly enhances the conductivity of thin film materials when synthesized under oxidizing conditions. The transport behavior for Sr-doped LaTiO 3 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)TiO 3 on biaxially textured Ni alloy tapes is demonstrated. These results suggest that (La,Sr)TiO 3 is a viable candidate as a conducting buffer for superconducting film growth on biaxially textured metal tapes.

Reel‐to‐Reel Continuous Chemical Solution Deposition of Epitaxial Gd2O3 Buffer Layers on Biaxially Textured Metal Tapes for the Fabrication of YBa2Cu3O7−δ Coated Conductors

A nonvacuum reel‐to‐reel dip‐coating system has been used to continuously fabricate epitaxial Gd2O3 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 Gd2O3 buffer layers have been studied. Highly textured films were obtained under reducing (96% Ar + 4% H2) atmosphere at temperatures between 1100° and 1150°C; postannealing speed did not significantly affect the crystalline quality of the Gd2O3. Scanning electron microscopy revealed a continuous, dense, and crack‐free surface morphology for these dip‐coated buffers. The Gd2O3 layer thickness led to pronounced differences in the growth characteristics of the subsequent YSZ and CeO2 layers deposited by rf‐magnetron sputtering. Epitaxial YBCO films grown by pulsed laser deposition on the short prototype CeO2/YSZ/Gd2O3/Ni–(3 at.% W–1.7 at.% Fe) conductors yielded self‐field critical current densities (Jc) as high as 1.2 × 106 A/cm2 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 CeO2/YSZ/Gd2O3 buffered Ni tapes by the industrially scalable ex situ BaF2 precursor process, exhibited end‐to‐end self‐field Jc values of 6.25 × 105 A/cm2 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.

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

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.