Thomas G. Chirayil

Epitaxial growth of La2Zr2O7 thin films on rolled Ni-substrates by sol-gel process for high Tc superconducting tapes

Abstract A solution process was used to grow epitaxial La 2 Zr 2 O 7 (LZO) buffer layers on roll-textured Ni (100) substrates to produce YBa 2 Cu 3 O 7− δ (YBCO)-coated conductors. The LZO precursor solution was prepared by an all alkoxide sol–gel route using mixed metal methoxyethoxides in 2-methoxyethanol. The partially hydrolyzed solution was either spin-coated or dip-coated onto the textured Ni substrates. The amorphous thin film was then heat treated at 1150°C under (96%)Ar/(4%)H 2 atmosphere for 1 h. X-ray diffraction (XRD) of the buffer layer indicated a strong c -axis orientation on the Ni (100) substrate. The LZO (222) pole figure revealed a single cube-on-cube texture. SEM images of the LZO buffer layer showed a dense microstructure without cracks. The YBCO deposited on the sol–gel LZO-buffered Ni substrates with sputtered YSZ and CeO 2 top layers had a critical current density of 480,000 A/cm 2 at 77 K and self-field.

Fabrication of long lengths of YBCO coated conductors using a continuous reel-to-reel dip-coating unit

A low-cost, non-vacuum, solution precursor route has been developed to produce epitaxial Gd/sub 2/O/sub 3/ and Eu/sub 2/O/sub 3/ buffer layers and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) superconductors on biaxially textured metal substrates. On sol-gel Eu/sub 2/O/sub 3/ seed layers with sputtered YSZ and CeO/sub 2/ top layers, a YBCO film with a J/sub c/ of over 1 MA/cm/sup 2/ at 77 K was obtained. On all solution buffer layers (CeO/sub 2//Eu/sub 2/O/sub 3//Ni), YBCO film with a J/sub c/ of 200,000 A/cm/sup 2/ at 77 K was grown using pulsed laser deposition (PLD). Meter lengths of epitaxial and crack-free Gd/sub 2/O/sub 3/ buffer layers were fabricated on cube textured Ni-W (3 at.%) substrates for the first time. High quality YBCO films were deposited on Rolling-Assisted Biaxially Textured Substrates (RABiTS) using a trifluoroacetate (TFA) precursor approach. The precursors were either spin-coated or dip-coated and decomposed in a newly developed fast 3-hour burn-out step followed by post-annealing. In a stationary burn-out route, we have produced 40 cm long crack-free YBCO TFA precursors on RABiTS. On short segments, YBCO films with a J/sub c/ of over 500,000 A/cm/sup 2/ at 77 K were grown on all PLD buffered-Ni substrates (CeO/sub 2//YSZ/CeO/sub 2//Ni).

Epitaxial growth of gadolinium oxide on roll-textured nickel using a solution growth technique

Chemical solution epitaxy was used to deposit an epitaxial film of Gd 2 O 3 on roll-textured nickel. A 2-methoxyethanol solution of gadolinium methoxyethoxide was used for spin-coating and dip-coating. Films were crystallized using a heat treatment at 1160 °C for 1 h in 4% H 2 /96% Ar. Single-layer films were approximately 600 A in thickness, and thicker films could be produced using multiple coatings. θ/2θ x-ray diffractograms revealed only (0041) reflections, indicating a high degree of out-of-plane texture. A pole-figure about the Gd 2 O 3 (222) reflection indicated a single in-plane epitaxy. Scanning electron microscopy showed that the films were smooth, continuous, and free of pin holes. Atomic force microscopy revealed an average surface roughness of 53 A. Electron diffraction indicated that the misalignment of the majority of the grains in the plane was less than 10°. High-current (0.4 MA/cm 2 ) Yba 2 Cu 3 O 7–δ films were grown on roll-textured nickel substrates using Gd 2 O 3 as the base layer in a three-layer buffer structure.

Preparation of Epitaxial YbBa2Cu3O7-δ on SrTiO3 Single Crystal Substrates Using a Solution Process

We have prepared YbBa2Cu3O7-δ (Yb-123) epitaxial films on SrTiO3 (100) single crystal substrates by a metal organic decomposition (MOD) method. Precursor solution was prepared by dissolving ytterbium acetylacetonate, barium neodecanoate, and copper (II) 2-ethylhexanoate in a mixture of solvents containing toluene/pyridine/propionic acid. The precursor solutions were spin coated on the substrates and fired at 730–770°C in 100-ppm oxygen atmospheres followed by 1 atm O2 annealing. X-ray diffraction results from the theta-2theta, phi, and omega scans for the films revealed a (100) cubic texture. The full-width-at-half-maximum values for Yb-123 (103) and Yb-123 (005) were 1.5° (in-plane epitaxy, Δ) and 0.73° (out-of-plane epitaxy, Δω), respectively. The highest Tc obtained for Yb-123 films was 87.2 K. The measured transport Jc was 6.4×105 A/cm2 at 77 K and self-field.

Epitaxial Growth of Yb2O3 Buffer Layers on Biaxially Textured-Ni (100) Substrates by Sol-Gel Process

In order to develop an alternative buffer layer architecture using the sol-gel process to produce YBCO (YBa2Cu307+) coated conductors, Yb203 has been chosen as the candidate material. Buffer layers of fi03 were epitaxkdly grown on biaxially textured-Ni (100) substrates by the sol gel process for the first time. The ~03 precursor solution was prepared from an alkoxide sol-gel route in 2-xnetho~ethanol and was deposited on textured-Ni (100) substrates by either spin coating or dip coating methods. The amorphous film was then processed at 1160oC under flowing (96%)MH2(4%) gas mixture for one hour. The fi03 iihn exhibited a strong c-axis orientation on the Ni (100) substrates. The phi and omega scans indicated good in plane and out of plane orientations. The X-ray (222) pde figure showed a cube-on-cube epitaxy. High current YBCO films were grown on the Y&03 sol-gel buffered-Ni substrates.

Solution Synthesis of Epitaxial Rare-Earth Oxide Thin Films on Roll-Textured Nickel

Using solution chemistry, epitaxial films of rare-earth oxides of the general formula RE 2 O 3 (where RE = Sm to Lu) were prepared on cubic-textured nickel tapes. Solutions of metal methoxyethoxides or metal acetate/methoxyethoxides in 2-methoxyethanol were used to coat rolltextured nickel tapes using either spin-coating or dip-coating. Coated tapes were subsequently heated in a reducing atmosphere at temperatures between 950 °C and 1160 °C for varying lengths of time. Film quality was determined using X-ray diffraction and electron and surface probe microscopy. Films were found to be oriented both in and out-of-plane of the substrate, free of pinholes and gross defects, and of sufficient quality for use as substrates for high T c , superconductors.