The widespread use of vacuum-based techniques for the deposition of ceramic coatings with specific electric, magnetic, optical, and mechanical properties is well established in the research environment, and some of them have been implemented in a variety of industrial processes. However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and in film thickness, and attaining independence of geometric constraints are areas in which many vacuum techniques will need sustained development in order to answer industrial demands. The development of the next generation of deposition methods, which could alleviate some of these shortcomings and which are based on deposition under atmospheric environment and from aqueous precursor materials, is a real challenge for the community of solid-state chemists and delineates the subject of this overview.

Recently, the sol-gel method has been developed as a potential alternative to the conventional vacuum techniques (e.g. pulsed laser deposition and magnetron sputtering) towards the synthesis of a coated conductor. The advantages of the sol-gel method include a more simple and faster way to deposit films, deposition at a lower cost and the possibility to incorporate it in a continuous system. Possible applications of these coated conductors are long lengths of superconducting cables, strong magnets, fault current limiters,… In our work, the coated conductor consists of a CeO 2 buffer layers and a YBa 2 Cu 3 O 7-δ superconducting film, coated on a textured substrate. Two kinds of substrates have been used in this work: ceramic R-cut (1102) sapphire substrate and metallic (001) Ni-alloy tape. For both substrates, a cleaning procedure was developed to improve the wettability. An almost complete wettability is necessary as an aqueous sol-gel method is used in this work. Dip-coating the cleaned substrates in the aqueous metal-citrate solution leaves a wet film on the substrate which can be converted to the ceramic oxide by thermal treatment. The dip-coating technique and thermal treatment were first optimized onto the sapphire substrate, as in the case of Ni-alloy, special attention is needed to avoid oxidation of the substrate. Due to the larger lattice mismatch, no biaxially textured CeO 2 could be obtained on R-cut sapphire substrate. However, on Ni-alloy tape, perfectly (001)-oriented CeO 2 is formed when the thermal treatment is performed in an Ar-H 2 atmosphere to avoid oxidation of the substrate. The results of microscopic and structural study of both CeO 2 and YBa 2 Cu 3 O 7-δ will be presented. Special attention will be given to the XRD and pole figure results, as these results give a good indication of the texture of the layers. Texture is of huge importance in the case of coated conductors, as in this way high critical current densities might be obtained.

Abstract. The widespread use of vacuum techniques for the development of coated conductors, in which buffer and superconducting (REBa 2 Cu 3 O 7- ) layers are deposited epitaxially on a substrate, is well established in the research environment. However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and in film thickness and attaining independence of geometric constraints are areas in which many vacuum techniques will need sustained development in order to answer industrial demands. This work describes the deposition of textured CeO 2 buffer layers based on sol gel dip coating under atmospheric environment and from aqueous precursor materials. Research has been performed towards the deposition of CeO 2 -buffer layers using the amorphous citrate method on sapphire substrates and Ni-W foils. Coating is performed using the dip-coating technique, which allows extension to a continuous system. The withdrawal speed and the thermal treatment have been optimised in order to obtain highly oriented (00l) layers exhibiting a smooth and crack-free morphology both on ceramic and metallic substrates. From the results it was concluded that sintering atmosphere and sintering temperature play a crucial role in the growth mechanism. This study describes the structural and morphological analysis of the thin layer with special attention to the difference between ceramic and metallic substrates. IntroductionThe development of high temperature superconductors, such as YBa 2 Cu 3 O x (YBCO), has resulted in many applications in the fields of electronics, microwave and conductor technologies. For this reason, ceramic superconductors have been deposited as thin films by various methods (e.g. pulsed laser deposition, sputtering, electron beam co-evaporation…) on many substrates, including SrTiO 3 , LaAlO 3 , MgO, Al 2 O 3 and flexible metallic substrates such as Ni and Ni alloys. These coated conductors are promising in the applications of transmission cables, motors, energy storage, magnets, fault current limiters, etc…. Excellent epitaxial relationships exist between YBCO and SrTiO 3 and LaAlO 3 1-3. These substrates however are expensive and are often only available in small sizes. For technical and industrially sized applications, the use of inexpensive and flexible metallic substrates becomes necessary. However, it has been shown that YBCO films deposited directly onto the latter substrates exhibit poor superconducting properties, because of chemical interactions and/or large structural mismatches 4. In order to grow a good quality YBCO thin film, it is necessary to use buffer layers such as CeO 2 5, Yttria-Stabilized Zirconia (YSZ) 6, MgO 7, SrTiO 3 8, BaZrO 3 9 etc. Amongst these, CeO 2 is usually considered as a high quality material, because of the good lattice match of the (100) plane with the YBCO (00l) plane, the comparable thermal expansion coefficient (11.6x10 -6 K -1 for CeO 2 , 12-13 x 10 -6 K -1 for YBCO), the oxidation

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Superconducting Bi-2223/Ag composites were prepared and the microstructure was thoroughly studied. A 20 nm thick amorphous–nanocrystalline phase was observed at the interface between the superconductor and the Ag. SEM/HREM/EDX observations were used to study this nanolayer and the results point to incongruent melting as the most probable cause of this phenomenon. The change in concentration of the Bi-2223 phase with the addition of Ag is elucidated in terms of the difference between the sintering temperature used and the incongruent melting. It is suggested that the frequently observed penetration of the ceramic phase into the Ag can be explained by the interfacial energy model.