O. Stadel

Continuous YBCO deposition onto moved tapes in liquid single source MOCVD systems

Abstract In a small scale MOCVD system YBCO films with j c(77 K ) > 1 MA were deposited onto substrates, which were continuously moved through the deposition chamber. Two routes for the buffer layer deposition onto textured Ni tapes were chosen: a) CeO 2 , LaMnO 3 and LaCrO 3 films were deposited in hydrogen atmosphere by MOCVD. On LaAlO 3 and R-Al 2 O 3 crystals epitaxial films were obtained b) textured NiO layers were grown by oxidation of textured Ni tapes. Based on the small scale system an enlarged MOCVD reactor was constructed.

MOCVD and MOD of YBCO and Buffer Layers on Textured Metal Tapes

Different layer architectures produced by only MOD, only MOCVD and combinations of MOD buffers and MOCVD YBCO are presented. RTR MOCVD-YBCO layers obtained on MOD-CeO2/MOD-LZO/Ni5 at%W tapes demonstrate critical current densities up to 2 MA/cm2 at 77 K. On single LZO (50-100 nm) buffered Ni5 at%W tapes from Nexans Superconductors and on RTR MOCVD buffer layers critical current densities between 0.8 and 1.3 MA/cm are obtained. RTR MOD-LZO layers often show delamination during YBCO deposition. Preannealing treatment before YBCO deposition allows to avoid this. Tapes up to 10 m are produced by combination of MOD-LZO and RTR MOCVD-YBCO.

MOCVD techniques for the production of coated conductors

New deposition techniques are used for MOCVD of YBCO-, buffer- and protective layers in a reel to reel system. This system consists of three tape reactors and evaporators. So it is possible to deposit the superconductor, the buffer layer and a protective layer in situ in one vacuum system. The operativeness of the reactors were tested separately. In the YBCO reactor superconducting films have been deposited with critical current densities over 1 MA/cm/sup 2/ at 77 K on moved textured Nickel tapes at a transport velocity of 4 m/h. Textured Ni substrates were coated in the buffer layer reactor with CeO/sub 2/ and in first experiments a Ag layer was deposited by MOCVD onto the YBCO film.

MOCVD of YBCO and Buffer Layers on Textured Ni Alloyed Tapes

A RTR MOCVD was used for the deposition of YBCO and various oxides. A new MOCVD technique enable us to coat the metal tape directly without formation of NiO. At a low oxygen partial pressure the buffer layers were grown on the metal tape with good in plane and out of plane texture. The texture of the MgO buffer layers depend on the surface of the alloyed Ni-tape. YBCO layers exhibit excellent out of plane texture with FWHM(005) = 1.4 - 3.5deg and good in plane texture of FWHM(103) = 5-7deg. On MgO buffered Ni5at%W the inductive measured jc was 0.3-0.7 MA/cm2 at 77 K.

MOCVD of YBCO and Oxide Buffer Layers on Textured Ni-Alloy Tapes

MOCVD technique was applied for deposition of oxide buffer layers onto magnetic and nonmagnetic Ni-alloy tapes at low oxygen partial pressure. YBCO was produced by MOCVD on CSD- and MOCVD-buffer layers. As a result, 1 μm thick YBCO layers were obtained with a critical current density of max. 1.5 MA/cm2, which corresponds to 150 A/cm-width. The new MOCVD setup with of several deposition reactors in a one reel-to-reel line was constructed for the single-pass low-cost production of up to 100 m long and 1 cm wide coated conductors with the tape velocity of 10-20 m/h.

High-temperature chemical vapor deposition. An effective tool for the production of coatings

Chemical vapor deposition (CVD) processes have a large throwing power and can operate at atmospheric pressure. Therefore, they are economical for many applications. High-temperature CVD processes give a good control of the crystal structure (e.g., epitaxial layers or other special layer structures) and support diffusion processes. The are used, for example, for the following deposition processes: 1) perovskites, 2) yttrium-stabilized ZrO2 layers as ion conductors or heat barrier coatings, 3) aluminide diffusion coatings in long tubes for corrosion protection, and 4) BN on fibers for fiber-reinforced materials. The special properties of the perovskite CVD are discussed in more detail. These processes are described for small- and large-scale applications. The CVD process is simulated by the computer code Fluent.

Electrically conducting oxide buffer layers on biaxially textured nickel alloy tapes by reel-to-reel MOCVD process

Reel-to-reel MOCVD process for continuous growth of electrically conducting buffer layers on biaxially textured Ni5W tapes has been developed. The new buffer layer architechture is presented: 200 nm (La, Ba)2CuO4/40 nm (La, Ba)MnO3/Ni5W. Constituting layers with high structural quality have been grown on moving tapes (in plane FWHM ≤ 6° and out of plane FWHM ≤ 3°).

Optical properties of buffer and superconducting layers of the YBa2Cu3O7 −δ/La1.75Ba0.25CuO4/La0.8Ba0.2MnO3 heterostructure for second-generation superconducting cables on an Ni5% W tape

An epitaxial YBa2Cu3O7 − δ/La1.75Ba0.25CuO4/La0.8Ba0.2MnO3 heterostructure has been obtained on a biaxially textured tape of an Ni5% W alloy. It is shown that when films of a buffer layer of La0.8Ba0.2MnO3 applied onto a tape of an Ni alloy in a reducing atmosphere are annealed in an oxygen atmosphere it is the compensation of oxygen vacancies that plays the dominant role in the formation of optical and magnetooptical properties of the layer, rather than stresses at the film-substrate interface. The shape of the reflection spectrum of the buffer layer after annealing corresponds to that of an La0.8Ba0.2MnO3 single crystal, which indicates that the oxygen content is close to the stoichiometric one. The temperature dependences of the transverse Kerr effect and coefficient of light reflection of the films at a fixed wavelength can be used for the evaluation of Tc and the temperature of the optical response of the metal-insulator transition of the buffer layer on the basis of lanthanum manganite.

MOCVD of coated conductors with electrically conductive buffer layers and their electrical field

A new MOCVD technique was developed for the deposition of oxides at a controlled low oxygen partial pressure, which enable to coat textured metal tapes with electrical conductive perovskites. In a RTR MOCVD-system metal tapes were coated with electrical conductive (La, Ba)MnO3, (La, Sr)MnO3, (La, Sr, Pb)MnO3 and (La, Ba)2CuO4 buffer layers and YBCO. In the same RTR-system YBCO was deposited on different buffered metal tapes. Computer calculations were used to characterise the behaviour for a weak superconducting part of a CC-tape with a conductive buffer layer system.

Chemical Vapor Deposition of Superconductor and Oxide Films

Chemical Vapor Deposition (CVD) of oxides is a very large branch in the field of CVD processes and is always a large part in books about CVD [1].