R.D. Blaugher

Processing of thick-film electrodeposited thallium oxide superconductors

Abstract Thick-film Tl-Ba-Ca-Cu-O superconductors (TBCCO) were synthesized on Ag foil and ceramic substrates using an electrodeposition process. The influence of Ag, initial stoichiometry, and reaction conditions on the phase development of TBCCO films were studied. Films deposited and reacted with no additional thallium source showed 1223 as the major phase, whereas films reacted using a two-zone thallation process showed 2223 as the primary phase formation. The TBCCO samples electrodeposited on Ag foil and annealed using the two-zone thallation process showed a critical current density of 3.2 × 10 4 A/cm 2 at 76 K in zero field. The highest critical current density for films reacted without any additional thallium source was near 10 4 A/cm 2 at 76 K in zero field.

Improved electrodeposition process for the preparation of superconducting thallium oxide films

Abstract We report on developing a two-layer process to deposit biaxially textured Tl-oxide films by electrodeposition (ED) on Ag-coated, single-crystal substrates. Pole-figure measurements of two-layer, electrodeposited (Tl,Bi)–(Sr,Ba)–Ca–Cu–O (TBSBCCO) films on 300 A Ag/LaAlO 3 (LAO), with thickness between 1 and 5 μm, clearly show strong biaxial texturing. The omega scan and phi scan of 1.6 μm (TlBi) 0.9 Sr 1.6 Ba 0.4 Ca 2 Cu 3 Ag 0.2 O x films indicate the full width at half maximum (FWHM) of only 0.92° and 0.6°, respectively, indicating a very high-quality film prepared by the ED process. Transport measurements for the electrodeposited, thallium-oxide-based superconductor films show values above 10 6 A/cm 2 at 77 K in zero field.

The study of critical current density of superconducting thallium oxide films from spray-deposited precursors

Abstract Spray deposition is a promising and economic approach for fabricating high-temperature superconducting films for the Tl-oxide superconductors. The Tl-oxides provide the potential for operation at 77 K in practical magnetic fields of 3– 5 T , which has been demonstrated by measurements on the irreversibility behavior of the Tl-1223 single layer compound with Bi and Sr substitution. In this report, we present the preparation and characterization of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 superconducting films fabricated from spray-deposited Tl-free, Ag-containing and Cu-rich precursors and reacted with thallium vapor using a two-step crucible process at 650°C/815°C in flowing argon for only 10/10 min . An epitaxial superconducting film was synthesized successfully and critical current densities of 8×10 5 A / cm 2 at 77 K in zero-field were obtained with excellent in-field performance.

Processing of Ag doped thick-film electrodeposited thallium-oxide superconductors

Abstract Thick-film superconductors of Tlue5f8Baue5f8Caue5f8Cuue5f8O (TBCCO) doped with Ag were synthesized on Ag foil using an electrodeposition process. Films deposited and reacted with or without an additional Tl source showed 1223 as the major phase. The transport critical current density for the film annealed in the presence of a TBCCO (2223) pellet was 14 630 A/cm 2 at 76 K in zero field and 8710 A/cm 2 at 76 K in zero field for the film annealed in the absence of any Tl source.

Low-calorie, high-energy generators and motors

Building on prototype motors and generators incorporating low-temperature superconductors, development of high temperature superconducting (HTS) counterparts is well along in Japan and the United States. In this article, the basic approach and principles of a superconducting AC synchronous generator or motor are described, and then the merits of using HTS field windings in their construction are assessed. Machines employing the early lower-temperature as well as the more recent high-temperature superconductors are discussed next. Finally, an update is provided on worldwide activities on developing a commercial generator and large motor utilizing superconductor windings.

Rapid furnace annealing of YBa2Cu3Ox thick films on Ni/NiO and inconel substrates prepared by spray pyrolysis of YBa2Cu3Ox powder

Abstract A spray pyrolysis growth system has been employed for the formation of superconducting YBa 2 Cu 3 O x (YBCO) thick films. YBCO films on polycrystalline Ni/NiO, Inconel 600, and Inconel X substrates ranging in thickness from 80–100 μm have been developed by a three-step process with observed T c zero values up to 85 K. In the first step, the metallic substrates were examined with and without a preoxidation anneal to form a native oxide layer. Second, superconducting YBCO powder (0.2 μm particle size) was mixed with ethanol and sprayed onto the substrates. Third, the films were sintered at high temperature and oxygenated to form the superconducting phase. The effect of a native oxide buffer layer upon superconducting properties was evaluated as a function of the duration of the preoxidation anneal and the sintering anneal. X-ray diffraction (XRD) θ/2θ, variable temperature four-probe resistance, and Auger line scan characterization of these films will be discussed.

Preparation of high-temperature superconductor oxide powders by electrodeposition

Abstract Superconducting precursor powders have been prepared using an electrodeposition process. The electrodeposition technique deposits all of the precursor components, including Tl , at the same time providing mixing on an atomic scale that reduces the reaction time to the order of minutes to obtain the desired phase development. The magnetization measurements of the annealed powder showed an intrinsic J c of about 10 5 A⧸cm 2 at 77 K in zero field. A current density near 10 4 A⧸cm 2 at 77 K in zero field was obtained for powder-in-tube (PIT) tape processed using electrodeposited precursor. This PIT tape showed the promising single-layer 1223 phase formation.

Superconducting thallium oxide and mercury oxide films

Abstract This paper reports on a study to convert electrodeposited Tl-oxide films to Hg-1212 using the cation-exchange process. A two-layer electrodeposition process was used to prepare Tl–Ba–Ca–Cu–O films with Tl-1212 and Tl-2212 stoichiometry. Electrodeposited Tl-films were also deposited with Bi and Sr substituted for the Tl and Ba, respectively and also reacted using cation exchange to attempt formation of Hg-1212. The superconducting transition temperature for the “non-substituted” films improved from 97 to 120 K after the cation-exchange process with a critical current density exceeding 2×10 6 at 5 K in zero field. The cation-exchange process for the Bi, Sr substituted films appears to be more difficult with no marked improvement in superconducting properties.

Superconducting (TlBi)/sub 0.9/Sr/sub 1.6/Ba/sub 0.4/Ca/sub 2/Cu/sub 3/Ag/sub 0.2/O/sub x/ films from electrodeposited precursors

A low-cost electrodeposition (ED) method is reported for fabrication of high-temperature Tl-oxide-based superconductors. Recent studies on the development of biaxially textured ED films on single-crystal and rolling-assisted biaxially textured Ni substrates are presented. Pole-figure measurements of electrodeposited (Tl,Bi)-(Sr,Ba)-Ca-Cu-Ag-O (TBSBCCO) films, with thicknesses between 1-5 /spl mu/m, clearly show strong biaxial texturing. The rocking curve and phi scan of TBSBCCO on 300 /spl Aring/ Ag/LaAlO/sub 3/, show a full width half maximum (FWHM) of only 0.9/spl deg/ and 1.2/spl deg/, respectively, consistent with a very high-quality. Transport measurements for the ED films show J/sub c/ values up to 7.84/spl times/10/sup 5/ A/cm/sup 2/ at 77 K in zero magnetic field. The preliminary results of electrodeposited TBSBCCO film on CeO/sub 2//YSZ/CeO/sub 2/ on textured Ni showed primarily 1212 phase with a transport critical current density of 1.36/spl times/10/sup 5/ A/cm/sup 2/ at 77 K in zero field.

Development of buffer layers for high quality Tl-Pb-Sr-Ba-Ca-Cu-O thick films on flexible metal substrates

Previous work has demonstrated the ability to grow extremely high quality Tl/sub 0.5/Pb/sub 0.5/Sr/sub 1.6/Ba/sub 0.4/Ca/sub 2/Cu/sub 3/O/sub x/ epitaxial films up to 15 /spl mu/m thick using melt growth techniques on single crystal LaAlO/sub 3/ substrates. This melt growth process is an ideal candidate for producing high quality superconducting films on flexible metal substrates with textured buffer layers; however, the textured buffer layer of choice, cubic yttria stabilized zirconia (YSZ), appears to be incompatible with the melt growth of TI-Pb-Sr-Ba-Ca-Cu-O films. In this work, we investigate textured buffer layers which are compatible with the epitaxial growth of Tl/sub 0.5/Pb/sub 0.5/Sr/sub 1.6/Ba/sub 0.4/Ca/sub 2/Cu/sub 3/O/sub x/ films. Crucial properties for the successful development of a suitable buffer layer are lattice matching, chemical stability and texture. Buffer layer materials investigated are CeO/sub 2/ and LaAlO/sub 3/ grown using a UV (248 nm) pulsed excimer laser deposition system equipped with multiple targets and a controlled ambient. Influence of substrate temperature and ambient gas pressure and flow on buffer growth are analyzed via XRD characterization. Highly textured buffer layers have been fabricated.