Optimization of Non-Fluorine Sol-Gel Derived YBCO Thin Films

Abstract

Sol-gel deposition of thin film YBa 2 Cu 3 O 7−δ (YBCO) is widely seen as the most cost effective means to manufacture long length HTS wires (A.P. Malozemoff, D.T. Verebelyi, S. Fleshler, D. Aized, and D. Yu, "HTS Wire: Status and Prospects," Physica C, 386, 424 (2003)). We present a sol-gel technique for YBCO deposition using low cost starting materials and forming only benign by-products during processing. Optimization has concentrated on producing the correct stoichiometry in the final films. RBS measurements show that copper diffuses into the substrate due to its high mobility at the temperatures required to form the YBCO phase. Therefore a starting stoichiometry of 1:2:3 can produce a film highly copper deficient. In order to compensate for this we have made films with different excesses of copper in the precursor solution. The surface morphologies of these films have been examined by SEM and AFM, and the stoichiometry and cation depth profiles characterized by ion beam analysis. The effect of the varying copper stoichiometry is correlated with the superconducting properties and the surface morphology for films on lanthanum aluminate (LAO) and magnesium oxide (MgO) substrates. The residual carbon concentration in the films is measured by nuclear reaction analysis.

Elucidation of the Mechanism in Fluorine-Free Prepared YBa2Cu3O7−δ Coatings

“…Fluorine-free CSD precursor solutions all consist of metal-salts that are stabilized in water and/or other solvents. − Upon transformation of the precursor state to the actual superconducting phase, the respective metal-salts are combusted to Y 2 O 3 , BaCO 3 , and CuO. Depending on the type of precursor and the atmosphere, combustion normally takes place below 500 °C.…”

“…17,18 Nevertheless, several papers report on the successful preparation of high critical current superconducting films from fluorine-free CSD precursors. [19][20][21][22][23] While most of these methods use organic solvents, we reported in a previous paper the synthesis of YBCO coatings starting from an aqueous solution. 24 In this work, we present a study of (i) the reaction mechanism responsible for the formation of YBCO from fluorine-free CSD precursors and (ii) the role of BaCO 3 in this.…”