Much of the conductor development effort in the last decade has focused on optimizing the processing of (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x oxide-powder-in-tube conductors and (Bi, Pb) 2 Sr 2 CaCu 2 O 8 (Bi-2212) and TlBa 2 Ca 2 Cu 3 O x thick film conductors. It is demonstrated that in each of these conductors, critical current densities are dictated by the grain boundary misorientation distributions (GBMD’s). Percolative networks of low-angle boundaries with fractions consistent with the active cross-sectional area of the conductor exist in each of these conductors. Further enhancements in the properties require increased numbers of small-angle grain boundaries. Given the processing methods used to fabricate these materials, no clear route employing a simple modification of the established processing method is apparent. To address this need, conductors with controlled or predetermined GBMD’s are necessary. Development of biaxial texture appears to be the only possible way to increase the number of small-angle boundaries in a practical and controllable manner. We summarize in this paper recent results obtained on epitaxial superconducting films on rolling-assisted-biaxially-textured-substrates (RABiTS). This technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield structurally and chemically compatible surfaces. Epitaxial YBa 2 Cu 3 O 7–δ films grown using laser ablation on such substrates have critical current densities exceeding 10 6 A/cm 2 at 77 K in zero field and have a field dependence similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of the next generation high temperature superconducting (HTS) wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high-temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 105 A/cm2 at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high-Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

Techniques are reported for sputter deposition of biaxially oriented buffer-layers on textured Ni tapes. These buffered tapes can be employed as long, flexible, or large area substrates for biaxially-aligned high-temperature superconductors (HTS) with high critical current density Jc. Using deposition techniques at temperatures as low as 25°C, epitaxial Pd or Pt films were first deposited as a base layer on the textured Ni tapes, followed by deposition of biaxially oriented Ag or CeO2 buffer layers. Using Ar/4%H2 sputter gas, biaxially oriented CeO2 films were also grown directly on the textured Ni tapes, followed by the epitaxial growth of YSZ films. All the films show both strong in-plane and out-of-plane orientations. The effects of Ni surface smoothness on buffer-layer texture were also investigated.

A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high-temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 10(5) A/cm(2) at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high-J(c) wire capable of carrying high currents in high magnetic fields and at elevated temperatures. (C) 1996 American Institute of Physics.

Anisotropie electrical resistivity is studied in epitaxial superlattice films of YBa2Cu3O7-jg/PrBa2Cu3O7-fk grown in situ by laser ablation on SrTiO3 surfaces aligned slightly away from the [100] direction. Layer thicknesses of each compound range from two to eight atomic cells. Electrical resistivity of these superlattice films always shows a peak at some cryogenic temperature that decreases with increasing PrBa2Cu3O7-fk layer thickness. Clear evidence is seen of vortex pinning or of supercurrent blocking by the step edges or by twin boundaries. The ratio of electrical resistivities for current directions parallel and perpendicular to these boundaries shows a large step-like change just above the superconductive critical temperature. The possibility is discussed that the Kosterlitz-Thouless transition explains this anisotropy change.

The use of low (cryogenic) temperatures to immobilize radiation-produced defects provides the capability to accumulate high defect concentrations having distributions greatly different from what is produced during ambient or high temperature irradiations. In addition to modifications of the low-temperature materials properties, a low-temperature irradiation followed by warmup can modify materials properties over a wide range of temperatures. As examples, irradiation-induced amorphization of NiTi, the release of stored energy in Cu, and the radiation-damage contribution to the superconducting critical current of Nb are described. The presently operating, low-temperature irradiation facilities at the Munich Research Reactor in Germany and the Kyoto University Reactor in Japan, are compared with facilities used at Oak Ridge National Laboratory.

Although the Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) high-temperature superconductors are known to possess superior flux pinning properties at high temperatures and in a large magnetic fields, the development of practical conductors has been severely limited by the existence of ``weak links`` at the grain boundaries. It is now established that strongly-linked, high J{sub c} YBCO materials can be produced in the form of bulk masses by a variety of melt-processing techniques. Here we describe a technique that couples a continuous fiber spinning process with zone-melt-processing, resulting in long lengths of high quality YBCO filaments that have microstructures and high-temperature electrical transport properties similar to those of melt-textured bulk materials.