Solution Refining for MOD-YBCO Optimization: An NMR Study

Abstract

In this paper, a study of both pure and 5% BaZrO33-doped YBCO low-fluorine coating solutions performed by 1 H-Nuclear Magnetic Resonance (NMR) spectroscopic techniques is presented. This investigation enabled us to unequivocally identify the chemical species involved in the solution aging process. It was found that the presence of traces of methanol, typically used for the preparation of the solutions, promoted methyl propionate formation. Since the methanol concentration reduction in time is not completely balanced by methyl propionate formation, it is supposed that additional esterification reactions involving other acids might occur. The presence of methyl propionate ester was not recognized in solutions obtained through a refining process in which residual methanol traces were fully removed. The modification in time of the solution composition was found to be in strong correlation with the degradation of the film properties for standard solution, whereas no degradation, in the same time frame, was observed for the films prepared with the refined solutions. Indeed, both YBCO and YBCO + 5% BaZrO 3 films, grown with aged refined solutions, exhibit critical temperature values above 91 K and microstructure comparable with the ones recorded in samples obtained with freshly prepared solutions. Even though the exact role of the ester in the YBCO phase formation and film quality could not be identified yet, some possible mechanisms have been proposed and discussed.