Flexible Metal Tapes Research Articles

Fabrication of Y123 coated conductors using metal organic decomposition process

Recent trends in HTS research have been geared toward development of coated conductors. In these conductors, a flexible metallic substrate, typically a nickel alloy, is covered successively with one or more thin buffer layer such as YSZ, STO, MgO, etc., and a relatively thick film of Y123. To make the fabrication of such conductors scalable and cost effective, this paper demonstrates the application of metal organic decomposition techniques to deposit the buffer layers and the YBCO films. We present results obtained strontium titanate buffer layers. These buffer layers, processed on single crystal substrates using solution precursors and heat treated in a reducing atmosphere are highly textured and have a uniform smooth surface. YBCO films, 0.3–0.5μm thick, deposited on these buffered single crystals using the trifluoroacetate process shows good superconducting properties. YBCO films processed on strontium titanate buffered lanthanum aluminate substrates have transition temperatures of 90–91 K and critical current densities of the order of 10 5 A/cm 2 at 77K and self field. These processing techniques have been extended to textured nickel substrates. These results offer promise to the development of a scalable, solution based processing route to deposit buffer layers and YBCO films on flexible metallic textured tapes.

Application of metal–organic decomposition techniques for the deposition of buffer layers and Y123 for coated-conductor fabrication

Recent developments in the fabrication of long length textured substrates have increased the focus on YBCO-based tapes for application as long-length conductors. A typical coated conductor consists of a metal substrate coated with a buffer layer on which YBCO is deposited in the form of a thick film. To make the fabrication of such conductors scalable and cost effective, this paper explores the possibility of applying metal–organic decomposition (MOD) techniques to deposit the buffer layers and the YBCO films. Two possible buffer layer candidates have been studied, namely, barium zirconate and strontium titanate. These buffer layers have been processed on single crystal substrates using solution precursors and heat treated in a reducing atmosphere, which makes the deposition techniques metal friendly. It has been found that these buffer layer films processed on single-crystal substrates are highly textured and have a uniform smooth surface. YBCO films, 0.3–0.5 μm thick, deposited on these buffered single crystals using the trifluoroacetate process, show good superconducting properties. YBCO films processed on barium zirconate buffered strontium titanate have transition temperatures of 86–88 K and critical current density of the order of 10 4 A/cm 2 at 77 K and self-field. YBCO films processed on strontium titanate-buffered lanthanum aluminate substrates have transition temperatures of 90–91 K and critical current densities of the order of 10 5 A/cm 2 at 77 K and self-field. These results offer promise to the development of a scalable, solution-based processing route to deposit buffer layers and YBCO films on flexible metallic textured tapes.

Relationship between film thickness and the critical current of YBa2Cu3O7−δ-coated conductors

During the development of YBa2Cu3O7−δ (YBCO) coatings on flexible metal tapes, it has become evident that the achievable critical current (Ic) reaches a maximum value of about 200 A per cm of conductor width at a coating thickness of 1–2 μm. Additional YBCO beyond this thickness can actually reduce Ic. To investigate, critical current density (Jc) has been measured for samples with YBCO ranging from 0.39 to 6.3 μm in thickness. Several films were thinned by ion milling and remeasured with two significant results: almost no supercurrent is carried at thickness levels above 2 μm; and for films thicker than 3 μm, Jc is drastically reduced near the substrate as well.

Metal–organic chemical vapor deposition as an emerging technique for the fabrication of YBa2Cu3Ox tapes

Abstract The deposition of YBa2Cu3Ox thin films on metal substrates is currently being investigated as the basis for future tape applications. The YBa2Cu3Ox coatings, discussed in this report, are deposited by metal–organic chemical vapor deposition (MOCVD). MOCVD is a versatile technique with many opportunities in terms of reaction chamber design and shapes of substrates to be coated. MOCVD equipment for fabrication of YBa2Cu3Ox coatings on long length, flexible metal tapes is currently being developed. Tapes of various materials, such as polycrystalline stainless steel, have been investigated. The growth of biaxially aligned buffer layers between the stainless-steel tapes and YBa2Cu3Ox coatings is necessary, to prevent interdiffusion, to reduce interfacial reactions and to allow the succeeding growth of aligned YBa2Cu3Ox thin films. The superconducting properties of the resulting YBa2Cu3Ox/buffer/substrate thin film systems, Tc≈90 K and Jc>105 A cm−2, are very promising. the major drawbacks in MOCVD of YBa2Cu3Ox thin films are the thermo-chemical properties of MOCVD precursors. For example, the traditional solid precursors have limited volatility. The development of new precursor delivery systems using precursor solutions and new solid and liquid precursors have resulted in improved process reliability. Finally, in the standard MOCVD process, which is thermally activated, the reported growth rates are approximately 0.5 μm h−1. An increase by one order of magnitude can be achieved in a photo-assisted MOCVD process.