Jean-Claude Grivel

A rapid process of YBa2Cu3O7−δ thin film fabrication using trifluoroacetate metal–organic deposition with polyethylene glycol additive

Trifluoroacetate metal–organic deposition (TFA-MOD) is a promising technique to fabricate YBa2Cu3O7−δ (YBCO) superconducting films. However, its slow pyrolysis process, which usually takes more than 10 h, constitutes a barrier for industrial production. In this study, polyethylene glycol (PEG) was utilized to reduce the stress generation inside the coated films when the strong pyrolysis reactions happen. With the addition of 30 wt% PEG2000 to the precursor solution, a smooth film surface could be obtained through a rapid pyrolysis process of 15 min. After the optimizations of the crystallization and oxygenation processes, mass percentage and molecular weight of PEG additive, YBCO thin films with Jc of about 4.5 MA cm−2 (77 K, self-field) could be routinely fabricated using (20–30) wt% PEG(1000–2000) additive with a total treatment time of about 2 h including the 15 min pyrolysis process time. The effects of PEG additive were discussed using one of the mechanisms of buckling formation. The reduction of compressive stress by PEG additive was suggested to be the reason for preventing buckling.

Study on Ce x La 1-x O 2 Buffer Layer used in Coated Conductors by Chemical Solution Method: Study on Ce x La 1-x O 2 Buffer Layer used in Coated Conductors by Chemical Solution Method

Developing multi-functional single buffer layer is one of the most important challenges for simplification of coated conductors configuration.La-doped CeO2 films were prepared by chemical solution method.And surface morphology and texture quality of the La-doped CeO2 films were investigated in details.The results show that the as-obtained pore-free Ce0.9La0.1O2 film are epitaxially deposited on the textured NiW substrate.The 120nm thickness Ce0.9La0.1O2 film is obtained though multi-coating route.The YBCO film with Tco=90.5K,which is deposited on Ce0.9La0.1O2/NiW metallic template by PLD method.It suggects that Ce0.9La0.1O2 film prepared by chemical solution route have a promising prospect for the simplification of coated conductors configuration.

A low-fluorine solution with a 2:1 F/Ba mole ratio for the fabrication of YBCO films

In previously reported low-fluorine MOD-YBCO studies, the lowest F/Ba mole ratio of the precursor solution was 4.5. Further lowering the F/Ba ratio would bring benefits for the environment, thick film deposition, and an understanding of the heat treatment process. On the other hand, the F/Ba ratio must be at least 2 for full conversion of the Ba-precursor to BaF2 to avoid the formation of BaCO3, which is detrimental to the superconducting performance of YBCO films. In this study, a solution with a 2:1 F/Ba mole ratio was developed, and the fluorine content of this solution was approximately only 10.3% of that used in the conventional TFA-MOD method. Attenuated total reflectance-Fourier transform-infrared spectra (ATR-FT-IR) revealed that BaCO3 was remarkably suppressed in the as-pyrolyzed film?and eliminated at 700??C. Thus, YBCO films with a critical current density (Jc) of over 5?MA?cm?2 (77?K, 0?T, 200?nm thickness) could be obtained on lanthanum aluminate single-crystal substrates. In?situ FT-IR spectra showed that no obvious fluorinated gaseous by-products were detected in the pyrolysis step, which indicated that all F atoms might remain in the film as fluorides. X-ray diffraction ?/2? scans showed the presence of BaF2?but not of Y F3 or CuF2?in films quenched at 400?800??C. The formation priority of BaF2 over Y F3 and CuF2 was interpreted by examining the chemical equilibrium of the potential reactions. Our study could enlarge the synthesis window of precursor solutions for MOD-YBCO fabrication, and serve as a foundation for continuously and systematically studying the influence of fluorine content in the precursor solutions.

Controlled growth of epitaxial CeO2 thin films with self-organized nanostructure by chemical solution method

Chemical solution deposition is a versatile technique to grow oxide thin films with self-organized nanostructures. Morphology and crystallographic orientation control of CeO2 thin films grown on technical NiW substrates by a chemical solution deposition method are achieved in this work. Based on an enhanced understanding of the effect of oxygen partial pressure during film crystallization, a strong texture can be obtained on the surface of the CeO2 films annealed at temperatures as low as 900 °C followed by a two-step annealing procedure. Crystallization at high temperature (e.g., 1100 °C) in a reducing atmosphere leads to the formation of an oxygen deficient CeO2−x phase coexisting with a small amount of a polycrystalline CeO1.67 phase. Further surface phase and texture analysis by an electron backscattering diffraction technique reveals that the off-stoichiometric CeO2−x phase retains a fluorite structure but exhibits an alternative in-plane texture with eight fold symmetry on the surface. According to phase and texture stability studies, these off-stoichiometric phases gradually transform back to fully oxidized CeO2 with a 45° rotated cube texture during storage in ambient air. Moreover, the morphology of the CeO2 thin films is controlled by precisely regulating the film thickness and crystallization temperature. A temperature-induced transition from the commonly observed granular grain to an atomically flat surface is found in the CeO2–NiW constitution. Cross-sectional transmission electron microscope observation also reveals that this phenomenon is mainly attributable to the surface re-organization, which is strongly associated with the critical film thickness, crystallization temperature, reducing ability of the crystallization atmosphere as well as the interface properties.

Epitaxial growth of YBa2Cu3O7−x films on Ce0.9La0.1O2−y buffered yttria-stabilized zirconia substrates by an all-chemical-solution route

In view of high rate fabrication of coated conductors at low-cost, YBa2Cu3O7 (YBCO) films on Ce0.9La0.1O2−y buffered yttria-stabilized zirconia substrates were deposited by means of a novel low-fluorine metal–organic solution route. A high critical current density of 3 MA cm−2 (77 K, self field) was achieved on such an all-chemical derived configuration. Structural characterization showed that the enhanced superconductivity performance of the YBCO films is mainly related to the defects induced by the interface.

Surface engineering of biaxial Gd2Zr2O7 thin films deposited on Ni–5at%W substrates by a chemical solution method

The surface texture and morphology of thin films play an essential role in determining their properties. In this study, local features in the film surface of crystallized Gd2Zr2O7 (GZO) films with a thickness gradient are investigated by means of scanning electron microscopy and electron backscatter diffraction. A strong dependence of the morphology and texture on the film thickness is observed, mainly due to (i) the transition of growth mode associated with the critical film thickness, i.e., increasing the film thickness leads to the grain morphology changing from 2-dimensional discs (highly ordered nanoislands or network) to 3-dimensional domes (equiaxed nanograins), and (ii) the segregation of residual carbon in the surface layer. The epitaxial nuclei forming at the interface hardly further develop by consuming the polycrystalline grains in the surface layer. A two-step annealing procedure is proposed to improve the surface texture in the GZO/NiW system, according to the influence of PO2 on the texture formation of GZO films. A GZO film with strong biaxial texture is achieved, as evidenced by the high indexing rate of Kikuchi patterns on the film surface, as well as by the highly ordered crystal structure along the film thickness observed by a transmission electron microscope. On the basis of the enhanced understanding of the crystallization processes, we demonstrate a possibility of engineering the surface morphology and texture in the film deposited on technical substrates using a chemical solution deposition route.

Growth of Highly Epitaxial YBa2Cu3O(7-δ) Films from a Simple Propionate-Based Solution.

Intensive investigations have been conducted to develop epitaxial oxide thin films with superior electromagnetic performance by low-cost chemical solution deposition routes. In this paper, a novel propionate-based precursor solution without involving any other additive was proposed and employed to grow superconducting YBa2Cu3O(7-δ) (YBCO) films on LaAlO3 (LAO) single crystals. The precursor solutions are stable with a long shelf life of up to several months. Since the primary compositions are propionates after evaporating the solvent, the toxic reagents and evolved gases during solution synthesis and heat treatment can be eliminated completely. In this process, rapid pyrolysis and high conversation rate can also be achieved during growth of YBCO films in comparison with the conventional trifluoroacetate metal organic deposition routes. Remarkably, a 210 nm YBCO film exhibits high superconducting performance with a Jc value of 3.7 MA/cm(2) at 77 K, self-field. Nucleation and growth behaviors in the chemical solution process have also been studied. It is revealed that the amount of liquid phase (Ba-Cu-O) is sufficient through the entire thickness within a very short time at high growth temperatures, which results in pronounced densification and fast conversion of the YBCO phase.

Kinetics of

We have studied the kinetics of the formation of from a stoichiometric mixture of Mg and 2B in Fe tubes using in-situ synchrotron powder diffraction at photon energies between E = 76-100 keV. Reaction with the sheath was studied in Fe tubes holding only Mg or B. We here demonstrate the use of a Pb absorber ring or aperture to damp the signals from the sheath material and thereby increase the quality of the diffraction pattern from the superconductor considerably. The new method has revealed a slow reaction between Mg and B when the temperature is below the melting point of Mg and a dramatic increase in the reaction kinetics as the Mg is melted. The reaction is complete on a timescale of the order 15-20 minutes after the Mg is melted.

{\rm MgB}_{2}

Monofilamentary Bi(2223) tapes have been prepared by the Powder-In-Tube technique using various alternatives for the final thermomechanical processing. In particular, both cold and hot deformation processes were investigated and their critical current densities at 77 K and 4.2 K were measured. For long cold rolled Bi(2223) tapes, transport j/sub c/ values up to 30000 A/cm/sup 2/ were obtained at 77 K and 0T. The value of j/sub c/ was found to increase from 17000 A/cm/sup 2/ at the oxide center to 46000 A/cm/sup 2/ at the borders of the oxide layer. At 4.2 K and 28 T, j/sub c/ values of 45000 and 30000 A/cm/sup 2/ were measured for B parallel and perpendicular to the tape surface, respectively. The j/sub c/ (B) hysteresis was found to disappear at higher fields. The present state of hot deformed Bi(2223) tapes is presented. For rolling temperatures up to 850/spl deg/C, a maximum of j/sub c/ (77 K, 0T)=18000 A/cm/sup 2/ was observed at 800/spl deg/C, j/sub c/ being considerably lower for higher rolling temperatures. The results obtained so far show generally lower j/sub c/ values than for cold rolled tapes. This is essentially due to microcracks and to sausaging effects, which are more pronounced than for cold rolled tapes. For static hot deformation at 800/spl deg/C of short, pressed Bi(2223) tapes an enhancement of j/sub c/ (77 K, 0T) by 20% up to >40000 A/cm/sup 2/ was observed. In addition, the decrease of j/sub c/ for B perpendicular to the tape surface is less pronounced compared to cold deformed tapes.<<ETX>>

Formation Studied by in-situ Synchrotron X-Ray Powder Diffraction

It is considered as a challenge for RABiTS route to get cube textured Ni-W alloy substrates with high mechanical and magnetic properties for coated conductors. The works of our group in recent years are summarized about different Ni-W substrates with high W content and composite tapes made by RABiTS technique. The fabrication process and the mechanism of cube texture formation in above different tapes are studied systematically. Compared with commercial Ni-5 at.%W substrate, these alloy substrates show a comparable texture quality and improved mechanical properties as well as reduced or zero magnetization especially in the novel composite substrates.