Shara S. Shoup

Epitaxial growth of BaZrO3 films on single crystal oxide substrates using sol-gel alkoxide precursors

Abstract Epitaxial BaZrO 3 (barium zirconium oxide) films were grown on single crystal substrates. A BaZrO 3 precursor solution was prepared by sol-gel synthesis using an all-alkoxide route. The barium precursors were prepared by reacting barium metal with 2-methoxyethanol, and zirconium precursors were prepared by exchanging ligands between zirconium n-propoxide and 2-methoxyethanol. The resulting BaZrO 3 precursor solution was partially hydrolyzed and spin-coated on sapphire (100), SrTiO 3 (strontium titanium oxide) (100), and LaAlO 3 (lanthanum aluminum oxide) (100) substrates. The films were post-annealed in oxygen at 800 °C for 2 min in a rapid thermal annealer. The coating and the annealing procedures were repeated three times to obtain the desired thickness, 300 nm. X-ray diffraction studies showed the presence of a single (100) cube texture for BaZrO 3 films on SrTiO 3 and LaAlO 3 substrates. The BaZrO 3 films grown on sapphire had a random texture. The BaZrO 3 films grown on SrTiO 3 substrates had a sharp texture compared to that on LaAlO 3 substrates. This may be due to the relatively smaller lattice mismatch between SrTiO 3 and BaZrO 3 .

SOL-GEL SYNTHESIS OF LAALO3; EPITAXIAL GROWTH OF LAALO3 THIN FILMS ON SRTIO3 (100)

A LaAlO{sub 3} precursor solution was prepared via an all alkoxide sol-gel route. The solution of lanthanum methoxyethoxide and aluminum methoxyethoxide in 2-methoxyethanol was prepared via ligand exchange starting from lanthanum isopropoxide and aluminum sec-butoxide and was used to make both LaAlO{sub 3} powders and films. Complete hydrolysis of the solution formed a gel that yielded well-crystallized LaAlO{sub 3} powders when fired in air at 800{degree}C. A partially hydrolyzed solution was spun-cast on SrTiO{sub 3} (100) single crystal substrates. Epitaxial films of LaAlO{sub 3} were subsequently formed during pyrolysis in O{sub 2} at 800{degree}C in a rapid thermal annealing furnace for a total of 8 min. The films were strongly c-axis oriented, verified by x-ray rocking curve results from the (003) plane with full-width at half-maximum (FWHM)=0.87{degree}, and had good in-plane texture shown by a {phi} scan of the (202) plane with FWHM=1.07{degree}. {copyright} {ital 1997 Materials Research Society.}

Sol-gel synthesis of LaAlO{sub 3}; epitaxial growth of LaAlO{sub 3} thin films on SrTiO{sub 3} (100)

A LaAlO{sub 3} precursor solution was prepared via an all alkoxide sol-gel route. The solution of lanthanum methoxyethoxide and aluminum methoxyethoxide in 2-methoxyethanol was prepared via ligand exchange starting from lanthanum isopropoxide and aluminum sec-butoxide and was used to make both LaAlO{sub 3} powders and films. Complete hydrolysis of the solution formed a gel that yielded well-crystallized LaAlO{sub 3} powders when fired in air at 800{degree}C. A partially hydrolyzed solution was spun-cast on SrTiO{sub 3} (100) single crystal substrates. Epitaxial films of LaAlO{sub 3} were subsequently formed during pyrolysis in O{sub 2} at 800{degree}C in a rapid thermal annealing furnace for a total of 8 min. The films were strongly c-axis oriented, verified by x-ray rocking curve results from the (003) plane with full-width at half-maximum (FWHM)=0.87{degree}, and had good in-plane texture shown by a {phi} scan of the (202) plane with FWHM=1.07{degree}. {copyright} {ital 1997 Materials Research Society.}

Low-cost combustion chemical vapor deposition of epitaxial buffer layers and superconductors

A new low-cost, open-atmosphere deposition technique, combustion chemical vapor deposition (CCVD) is used to deposit epitaxial buffer layers and high-temperature superconductors on oxide single-crystal substrates. The CCVD process has the potential for manufacturing buffer layers and superconductors onto textured metal substrates in a continuous reel-to-reel production. CCVD does not use vacuum equipment or reaction chambers required by conventional techniques, while its coating quality rivals and even exceeds that of conventional methods. Compounds being studied with the CCVD process include the buffer layers cerium oxide (CeO/sub 2/), yttria stabilized zirconia (YSZ), strontium titanate (SrTiO/sub 3/), lanthanum aluminate (LaAlO/sub 3/), yttria (Y/sub 2/O/sub 3/), and ytterbium oxide (Yb/sub 2/O/sub 3/) and two rare earth superconductors, YBa/sub 2/Cu/sub 3/O/sub 7-x/, (YBCO) and YbBa/sub 2/Cu/sub 3/O/sub 7-x/ (YbBCO).

The progress made using the combustion chemical vapor deposition (CCVD) technique to fabricate YBa/sub 2/Cu/sub 3/O/sub 7-x/ coated conductors

Combustion Chemical Vapor Deposition (CCVD) is a nonvacuum technique being investigated, in conjunction with the Rolling Assisted Biaxially Textured Substrates (RABiTS/spl trade/) process, as a method to fabricate low-cost, long-length Yttrium Barium Copper Oxide (YBCO) coated conductor tapes. This technique has been scaled to produce meter + lengths of buffer material with excellent epitaxial and microstructural uniformity along the length. Additional efforts focus on depositing YBCO on these lengths using several deposition techniques including CCVD. Pulsed laser deposition (PLD) YBCO with critical current densities >1 MA/cm/sup 2/ have been achieved on short coupons taken from meter lengths of CeO/sub 2//STO/Ni architectures. CCVD buffer layers on Ni-W are still being optimized as YBCO critical current densities are less than 50,000 A/cm/sup 2/. The critical current densities of coupons of YBCO deposited by CCVD onto CCVD buffered substrates is increasing up to 100,000 A/cm/sup 2/, but further optimization is needed to yield high performance samples.

Syntheses of Titanate-Based Hosts for the Immobilization of Pu(III) and Am(III)

Syntheses of novel titanate-based waste forms, potentially suitable for immobilizing Pu(III) and Am(III), have been performed. The dititanate compounds An{sub 2}Ti{sub 2}O{sub 7} (An = Pu or Am) were found to have a monoclinic structure. A series of pyrochlore-type solid solutions between An{sub 2}Ti{sub 2}O{sub 7} and the cubic pyrochlore Ln{sub 2}Ti{sub 2}O{sub 7} (Ln = Gd, Er, or Lu) has been established, and limits of solid solubility for An{sub 2}Ti{sub 2}O{sub 7} were determined. These limits were found to increase as the ionic radius of the lanthanide in the host decreased. Strontium-containing titanate compounds SrAn{sub 2}Ti{sub 4}O{sub 12} were also prepared and were characterized as exhibiting a perovskite-type structure. Such compounds could serve as waste hosts for the immobilization of not only the actinide but also {sup 90}Sr. A 2 month leaching study of Er{sub 1.78}Pu{sub 0.22}Ti{sub 2}O{sub 7} and SrPu{sub 2}Ti{sub 4}O{sub 12} by WIPP A brine was performed. Very low amounts (<1 ppm) of Pu(III) were leached. Although the ionic radius of Np(III) is similar to that of Pu(III) and Am(III), analogous Np compounds could not be prepared in any of the titanate systems investigated.

Development of CCVD ceramic insulation for Bi-2212 superconducting wires and Rutherford cables

A low cost, open-atmosphere deposition technique, Combustion Chemical Vapor Deposition (CCVD) is used to deposit zirconia-based, multi-component insulation films on Bi-2212 tapes for fabricating high temperature superconducting magnet coils. The insulation coatings were investigated in detail in terms of composition, microstructure, and insulation strength versus the deposition temperature and other parameters. Dielectric and mechanical properties and chemical compatibility with BSCCO have been characterized and optimized. The advantage of the CCVD technique in producing multi-component insulating materials with the desired properties are described. A brief evaluation of this insulation coating on Rutherford cables fabricated from Bi-2212 wires is also reported.

Processing of Long-Length Tapes of High-Tempera Ture Superconductors by Combustion Chemical Vapor Deposition

The Combustion Chemical Vapor Deposition (CCVD) technique presents an attractive route for the deposition of low-cost, practical lengths of second-generation coated superconductors. CCVD-deposited buffer layers on textured nickel substrates have enabled high-performance superconductors of greater than 1 MA/cm2. Thin films of YBCO deposited by CCVD exhibit excellent materials characteristics (epitaxy, composition, and microstructure) and electrical properties on single crystal substrates with critical current densities greater than 1MA/cm2. The CCVD technology is very amenable to scale-up as has been demonstrated by the fabrication of 1 and 10 m lengths of buffered nickel. The incorporation of ccvd superconductor depositions can also be easily realized. Because of the inexpensive chemical and capital equipment costs, CCVD is well-positioned to fabricate commercial quantities of YBCO-coated conductor that meet DOE’s cost target of

High-Temperature Superconducting Tapes Deposited by the Non-Vacuum, Low-Cost Combustion Chemical Vapor Deposition Technique

10/kA-m.

ON THE FORMATION OF AMERICIUM-AND NEPTUNIUM-CONTAINING TITANATES

The enormous technological potential of high-temperature superconductors (HTS) was realized immediately following their discovery in 1986, yet these materials largely remain laboratory curiosities as scientists struggle to scale from coupons to long lengths of practical coated conductor. Although both vacuum and non-vacuum processes are being investigated for commercial production, low-throughput vacuum techniques were the first to succeed in producing the buffer and superconducting layers necessary for superconducting tape with high critical currents. However, vacuum processes are not only expensive but impractical when addressing the needs for rapid production of kilometer lengths of wire. The innovative Combustion Chemical Vapor Deposition (CCVD) method used with the Rolling Assisted Biaxially Textured Substrates (RABiTS™) technology has shown significant promise in fabricating the multi-layer structures necessary for successful HTS tape while overcoming many of the shortcomings of traditional vacuum techniques. The key advantage of the CCVD technology is its ability to deposit high quality thin films in the open atmosphere using inexpensive precursor chemicals in solution. As a result, continuous, production-line manufacturing is possible with significantly reduced capital requirements and operating costs when compared to competing vacuum-based technologies. The current status of development for production of long lengths of high-temperature superconductors using CCVD will be discussed.