Joseph Schaubroeck

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

In this work, the reaction mechanism used in the preparation of fluorine-free superconducting YBa(2)Cu(3)O(7-delta) (YBCO) was investigated. To determine which precursor interactions are dominant, a comprehensive thermal analysis (thermogravimetric analysis-differential thermal analysis) study was performed. The results suggest that a three step reaction mechanism, with a predominant role for BaCO(3), is responsible for the conversion of the initial state to the superconducting phase. In the presence of CuO, the decarboxylation of BaCO(3) is kinetically favored with the formation of BaCuO(2) as a result. BaCuO(2) reacts with the remaining CuO to form a liquid which ultimately reacts with Y(2)O(3) in a last step to form YBCO. High temperature X-ray diffraction experiments confirm that these results are applicable for thin film synthesis prepared from an aqueous fluorine-free sol-gel precursor.

Comments on the wetting behavior of non-porous substrates for ceramic coated-conductor applications

This work gives an overview of the possibilities to improve the wetting behavior of precursors for coated conductors on non-porous substrates. Within this work, all coatings were performed on a metallic Ni–W/La2Zr2O7/CeO2 substrate using water-based Y, Ba, Cu containing precursors. The results described in this paper can be used for different technologies of chemical solution deposition, as there are ink jet printing, dip coating, spin coating etc. Starting from the forces involved during wetting, a separation between solid and liquid modifications was made. This study revealed that if a good cleaning procedure of the substrate, whether or not combined with a targeted modification of the precursor is applied, water-based solutions can be used without restriction towards their wetting behaviour leading to a sustainable technology within the coating industry. Within this work, special attention is given to (1) fast determination of the substrate cleaning procedure quality by the creation of wetting envelopes and (2) the use of a screening design of experiment to study the effects of intrinsic solution factors, such as precursor formulation, influencing the coating behavior. All modification discussed are expandable to all kinds of precursors and substrates.

Accurate determination of the composition of Y-Ba-Cu-O superconductor by spectrophotometry, gravimetry and flame AAS

A procedure for the accurate analytical determination of yttrium, barium and copper in an YBa2Cu3Ox superconductor is described. After dissolution of the material the concentration of Y and Cu was spectrophotometrically determined as an Y–Arsenazo III and a Cu–Nitroso-R-salt complex, respectively. Ba was determined either gravimetrically as BaCrO4, after precipitation using a K2CrO4 solution or using flame atomic absorption spectroscopy (AAS). An accuracy better than 0.7% and a coefficient of variation better then 1.2% are obtained. It is illustrated that this analytical procedure can be used to determine the composition of a bulk superconducting YBa2Cu3Ox sample. For determination of Ba in thin films we suggest the use of flame AAS, with an accuracy of 0.03% and a coefficient of variation of 1.7%.