Showing papers by "S. R. Foltyn published in 2000"

The microstructure of continuously processed Yba2Cu3Oy coated conductors with underlying CeO2 and ion-beam-assisted yttria-stabilized zirconia buffer layers

Abstract: The microstructural development of YBa2Cu3Oy (Y-123) coated conductors based on the ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) to produce a biaxially textured template is presented. The architecture of the conductors was Y-123/CeO2/IBAD YSZ/Inconel 625. A continuous and passivating Cr2O3 layer forms between the YSZ layer and the Inconel substrate. CeO2 and Y-123 are closely lattice-matched, and misfit strain is accommodated at the YSZ/CeO2 interface. Localized reactions between the Y-123 film and the CeO2 buffer layer result in the formation of BaCeO3, YCuO2, and CuO. The positive volume change that occurs from the interfacial reaction may act as a kinetic barrier that limits the extent of the reaction. Excess copper and yttrium generated by the interfacial reaction appear to diffuse along grain boundaries and intercalate into Y-123 grains as single layers of the Y-247, Y-248, or Y-224 phases. The interfacial reactions do not preclude the attainment of high critical currents (Ic) and current densities (Jc) in these films nor do they affect to any appreciable extent the nucleation and alignment of the Y-123 film.

Advances in ybco coated conductor technology

Abstract: Processes for producing both the yttrium-stabilized zirconia (YSZ) template film by ion beam-assisted deposition (IBAD) and the YBa 2 Cu 3 O x (YBCO) superconducting film by pulsed laser deposition (PLD) at 1-m lengths have achieved I c values of 122 A and J c values of 1 MA/cm 2 . Improvements have been made in all stages of the process. Variations of I c along the length of the 1-m samples stimulated development of a new in-field I c measurement capability. The use of MgO as an IBAD template film has made great progress and can potentially decrease the time to produce the template film by more than an order of magnitude. A combination of electrical and microstructural investigations is being made to understand and improve the properties of the YBCO-coated conductors.

Alternating current losses in YBa2Cu3O7−x coated conductors on technical substrates

Abstract: We report on measurements of the ac losses of YBa2Cu3O7−x conductors on technical substrates. The samples are taken from conductors 1 m long produced with an ion beam assisted deposition step in the manufacturing process yielding 1 cm wide conductors with critical currents approaching 100 A at 77.4 K. The losses due to combinations of ac transport currents and ac magnetic fields were measured calorimetrically and the results compared to theoretical estimates. While the results of our measurements are similar to the theoretical estimates, there are some important differences in the qualitative behavior.

Development of meter-long YBCO coated conductors produced by ion beam assisted deposition and pulsed laser deposition

Abstract: A “second-generation” of high Tc conductors, consisting of YBCO coatings on flexible metal substrates, has recently reached a milestone with meter-long tapes capable of carrying over 100 A in a 1 cm width at liquid nitrogen temperature. Having reached this level of performance, however, we have encountered difficulties in the self-field characterization of such high current material. In particular, measurement of critical current uniformity along the tape length has in some cases resulted in damage to weaker tape segments during measurement of higher-current ones. To address this problem we have developed a novel measurement technique that uses permanent magnets to locally suppress the critical current of the tape section being measured to a level that is “safe” for the rest of the tape.

Improved superconducting properties of SmBa2Cu3O7−δ films using YBa2Cu3O7−δ buffer layers

Abstract: We report the fabrication of SmBa2Cu3O7−δ (Sm123) films on YBa2Cu307−δ(Y123) buffer layers 10–20nm thick using pulsed-laser deposition. Significant improvement in the superconducting properties of Sm 123 such as Tc and Jc has been observed when Y123 buffer layers are used on various substrates (LaAlO3, SrTiO3, NdGaO3 and CeO2/(yttrium-stabilized zirconia)). The buffered Sm 123 films have a high Tc of 93.1 K and a high Jc of 1.9 × 106 Acm−2 at 75 K in zero magnetic field. Compared with Y123, the buffered Sm123 samples have com-parable microwave surface resistance values and pinning characteristics with reduced anisotropy measured by the angle-dependent Ic. The effects of the Y123 buffer layer on the superconducting properties of Sm 123 are investigated and discussed in relation to the initial film growth chemistry and the substitution of Sm on Ba sites.

YBCO Coated Conductor Current Lead Testing

Abstract: Current leads formed from YBCO coated conductors have been tested at the Superconductivity Technology Center (STC) at Los Alamos National Laboratory. The test facility at STC provides conductive cooling for binary current leads, i.e. a warmer conventional lead section joined to a colder high temperature superconducting (HTS) section. Cryogenic heat pipes filled with nitrogen are used as electrically isolated thermal intercepts at the junction of the conventional and the HTS sections. Temperatures are controlled at the warm and cold ends of the HTS sections. Refrigeration is provided by a mechanical cryocooler. Self-field critical current measurements ranging from 0 to 200 A are reported for conduction cooled leads in a vacuum with warm and cold end temperatures varied as parameters. These critical current measurements are compared with critical current measurements made on the same components in a 75 K liquid nitrogen bath. It is found that the critical current of the conduction-cooled leads is nearly twice that measured in liquid nitrogen when the warm end of the leads is held at 70 K and the cold end is held at 60 K.

High Temperature Superconducting Quantum Interference Devices in a Superconductor-Normal-Superconductor Geometry

Abstract: The discovery of high temperature superconductors (HTS) has led to intense interest in the fabrication of thin films and Josephson Junctions from the new materials. Most of the Josephson junction work has focused on the bicrystal approach[l]. In this method bicrystal substrates are used to produce a single coherent large angle grain boundary in epitaxial films of HTS. This method has produced most of the best junction results to date [2], but requires an expensive substrate and limits the flexibility of the junction placement.