Jeffrey Todd Dawley

All solution-chemistry approach for YBa2Cu3O7−δ-coated conductors

A need exists for low-cost coated-conductor fabrication methods for applications in magnet and electric-power technologies. We demonstrate high-critical current density (Jc) YBa2Cu3O7−δ (YBCO) films grown on Nb-doped SrTiO3 (Nb:STO) buffered Ni(100) tapes. All buffer and superconductor layers are deposited using solution chemistry. A 50 nm thick Nb:STO seed layer on Ni(100) acts as a template for the growth of subsequent thicker layers of Nb:STO. Nb doping improves the electrical conductivity and oxygen diffusion barrier properties of STO. YBCO grows heteroepitaxially directly on this buffer layer, resulting in a transport Jc(77 K)=1.3 MA/cm2.

Chemical solution deposition of -oriented SrTiO3 buffer layers on Ni substrates

Biaxially textured -oriented SrTiO 3 films were solution deposited on LaAlO 3 single crystals and -oriented polycrystalline Ni tapes. Solution variables including varying titanium alkoxide chain length, inclusion of chelating agents, and inclusion of donor dopant, were investigated for their effect on film orientation, morphology, and oxygen diffusivity. The best SrTiO 3 orientation on high lattice mismatch (11%) Ni substrates was achieved through use of a discontinuous nucleation seed layer, which provided nucleation sites for subsequent continuous SrTiO 3 films. Increased titanium alkoxide chain lengths appeared to suppress titanium hydrolysis reactions and improve film orientation. 1 3 C nuclear magnetic resonance showed that significant quantities of water were generated due to esterification reactions, which appeared to cause hydrolysis and subsequent orientation degradation in the absence of chelating agents such as acetylacetone.

Thick sol-gel derived YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films have been prepared by spin-coating solutions of metal acetates dissolved in trifluoroacetic acid/methanol and trifluoroacetic acid/isopropanol/1,3 propanediol onto LaAlO/sub 3/[100] substrates. By using a rapid, low pO/sub 2/ pyrolysis process, high-quality diol films (0.25 /spl mu/m thick) with J/sub c/ values as high as 14 MA/cm/sup 2/ and 2 MA/cm/sup 2/ at 7 K and 77 K, respectively, were fabricated in one tenth the time, compared to conventional processing schemes. The effect of multicoating, in order to reach YBCO film thicknesses of 1.5 /spl mu/m, on the J/sub c/ was also studied.

Improving sol-gel Yba 2 Cu 3 O 7−δ film morphology using high-boiling-point solvents

The effect of high-boiling-point solvent addition on the morphology of low-p(O 2 ) processed, sol-gel YBa 2 Cu 3 O 7 - Φ (YBCO) films is discussed. Proper selection and addition of a high-boiling-point solvent prevents film roughening during precursor pyrolysis, while permitting at least a tenfold reduction in pyrolysis time compared to standard film processing in air or O 2 . Use of such solvents appears to increase film plasticity, avoiding elastic compressive stress related buckling. High-quality YBCO films on LaAlO 3 with a critical current density (J c ) ∼ 3-4 MA/cm 2 at 77 K, are routinely crystallized with this new sol-gel process. Diethanolamine-based, sol-gel YBCO films deposited on sol-gel SrTiO 3 -bufiered Ni have J c (77 K) > 1 MA/cm 2 , demonstrating a route toward all-sol-gel superconducting wires.

Chemical solution deposition of biaxially oriented (Ba,Sr)TiO 3 thin films on 〈100〉 Ni

Biaxially oriented Ba 1 - x Sr x TiO 3 (BST) thin films were fabricated under a highly reducing atmosphere (oxygen partial pressure ∼10 - 1 8 atm) on base metal substrates ((100) Ni) using a fluorinated chemical solution deposition method. The degree of film orientation was investigated with respect to film annealing temperature and composition (x = 0, 0.33, 0.5, 0.67, 1). The solution synthesis route included fluorinated solvents, donor-dopants, and chelating agents for control of orientation, defect chemistry, and morphology. Free-energy and phase diagrams guided solution development using halide addition to avoid intermediate BaCO 3 formation and instead produce direct crystallization of BaTiO 3 -type materials from BaF 2 . The degree of (200) orientation of BST films deposited on (100) Ni substrates displayed a compositional dependence for 0 < x < 1, with a maximum orientation Lotgering factor approaching unity. Low-temperature (500 °C) crystallization of highly oriented films was demonstrated for solution-derived BST on Ni, which may have enabling materials integration implications for capacitors and other applications.

Optimizing SrTiO3 films on textured Ni substrates using chemical solution deposition.

(100) (BCT) templates on textured W-dopedNi(100) (Ni:W) tape substrates. The BCT template films form a thin layer or “skin”that bridges its significant porosity. STO films grown at 1000 °C appear optimized forheteroepitaxial orientation, surface coverage, and film smoothness. Both interfaces inthe STO(100)/BCT(100)/Ni:W(100) stack demonstrate excellent atomic registry andcompositional abruptness. Doping STO with a few atomic percent of Nb reducesoxygen diffusion into the film by an order of magnitude and provides greaterprotection to the Ni interfacial surface from oxidation during the growth of additionalfunctional oxides requiring relatively higher p(O

Properties of YBa 2 Cu 3 O 7−δ multilayer films from the fluoride-based sol-gel process

The inability to rapidly grow thick or multilayer epitaxial films for either electronic or electrical power applications limits the utility of fluoride-based processes for YBa2Cu3O7−d (YBCO). This problem is due to the use of water vapor in the growth process, necessary for the dissociation of metallofluorides. Flowing wet gas at low temperatures is corrosive to cuprates and responsible for destroying underlying YBCO layers in attempts to grow secondary layers. This is avoided simply by increasing the temperature where vapor is introduced into the growth ambient. Resulting two-layer films of YBCO have properties similar to those of high critical current density single-layer films.