Deposition of CeO₂ Buffer Layers and YBa₂ Cu₃O_7-δ Superconducting Layers Using an Aqueous Sol-Gel Method

Abstract

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.

Thin YBa2Cu3O7-δpatterns by Chemical Solution Processing using Ink-Jet Printing

“…In recent years, a lot of research has been dedicated to the development of low cost, fluorine-free, preferably aqueous precursor solutions for the chemical deposition of YBCO and buffer layers [33][34][35][36]. We have recently published that the use of chelating agents such as NTA and triethanolamine to increase the ion solubility can lead to excellent YBCO precursors [26,37].…”

Influence of Morphology and Texture of CeO2 on YBa2Cu3O7 (YBCO) Growth and BaCeO3 Formation in Solution‐Derived Synthesis

“…[14,16,31] Ce(NO 3 ) 3 (Sigma-Aldrich, Ce III nitrate hexahydrate) was used in a 0.45 m concentration in a 1:3 ratio with citric acid (Carl Roth, citric acid monohydrate, Ͼ99.5 %). The pH was set at 6.1 using ammonia (Carl Roth, ammonia, 25 %).…”

“…[9][10][11][12][13] The deposition of both buffer layers and YBCO starting from aqueous precursors by using dip coating was described by us previously. [1,[14][15][16][17] In this approach, metal salts are dissolved in water in the presence of appropriate complexing agents, thus leading to the formation of metal-chelate complexes, which is necessary to control hydrolysis of the metal salts. [18] To minimize chemical interactions and optimize crystal growth of the superconducting YBCO layer, an efficient buffer layer architecture of sufficient thickness is required in between the metal tape and the superconducting layer.…”

CeO2 Buffer Layers for HTSC by an Aqueous Sol‐Gel Method – Chemistry and Microstructure

“…The cleaning process involved both a thermal and a chemical cleaning. [19] The substrates were heated to 800°C under ambient Ar-(5 %)H 2 atmosphere followed by a chemical cleaning consisting of a degreasing and decontaminating phase, respectively in trichloroethylene, acetone, methanol and water. An etching phase, in a 1:1 mixture of formic acid and hydrogen peroxide, was subsequently applied in order to increase the wettability of the substrate due to deformations of the grain boundaries and smoother surfaces.…”

“…[19][20][21] Starting from the thermal process in Figure 4, we mainly focused on the sintering step (at approximately 1050°C) and its according ambient Ar-(5 %)H 2 atmosphere.…”