J Schaubroeck

A water-based sol–gel technique for chemical solution deposition of (RE)Ba2Cu3O7−y (RE = Nd and Y) superconducting thin films

The achievement of low-cost deposition techniques for high critical current (RE)Ba2Cu3O7?y-coated conductors is one of the major objectives in achieving a widespread use of superconductivity in power applications. Chemical solution deposition techniques are appearing as a very promising methodology to achieve highly textured oxide thin films at a low cost, so an intense effort is being carried out to develop routes for all chemically coated conductor tapes. In this work recent achievements will be presented towards the goal of the development of an environmentally friendly, completely water-based sol?gel technique for the deposition of thin superconducting films on SrTiO3 single-crystal substrates using the dip coat technique. A comparison is made between aqueous sol?gel synthesis of two (RE)Ba2Cu3O7?y superconducting systems: YBa2Cu3O7?y and its homologue NdBa2Cu3O7?y. Our conclusions are that YBa2Cu3O7?y still remains the material of choice for coated conductor development using this sol?gel technique, with a Tc,onset of 91?K and Jc of 0.3?MA?cm?2.

Characterisation of the sol–gel process in the superconducting NdBa2Cu3O7−y system

The objective of this paper is to obtain a better insight into the sol–gel mechanism of water-based precursors for the development of thin NdBa2Cu3O7−y (NBCO) superconducting films. The influence of metal complexation behaviour on the formation of transparent and homogenous gels after the combination of different metal salts and ligands has been studied for several metal salts (Cu2+, Nd3+ and Ba2+). Two inorganic aqueous sol–gel precursors have been studied: a metal nitrate–citric acid-based and a metal acetate–triethanolamine-based solution. The characteristics of the precursor solution are based on the determination of the stability constants by the computer program Superquad. The prediction of the complex stability in this solution was related to the complexation of the three metal ions (Cu2+, Nd3+ and Ba2+) with a certain ligand. IR-spectroscopy was used for the determination of the gel. This resulted in a better understanding of the composition of the solution and could be used for preparation of more stable sol–gel precursors for the synthesis of homogeneous end products. These sol–gel systems were used for the deposition of highly textured superconducting thin films on SrTiO3 substrates by dip-coating. Using detailed thermal analysis, it is shown that the morphology of the films can be optimised by adjusting the parameters during thermal treatment, resulting in dense and highly textured thin films. Special attention is given to the microstructure of the thin film because of its relevance to the superconducting transport properties of the coated conductor system.