Chemical analysis in YBa2Cu3O7−x melt-textured samples

Abstract

A melt-textured process that involves the peritectic reaction Y2BaCuO5 + liquid → YBa2Cu3O7−x is the best method to develop bulk YBa2Cu3O7−x superconductors with improved transport and magnetic properties. Up to this point, information regarding cationic stoichiometry in textured samples is rather lacking in the literature. In this work, wavelength dispersive analysis (WDS) at a microscopic level and energy dispersive x-ray analysis (EDX) at a nanoscopic level were used to characterize the chemical composition of YBa2Cu3O7−x textured samples. The melt-textured process generally modifies the sample stoichiometry. Thus, a textured sample composition cannot be directly obtained even from an accurate knowledge of the starting composition. We have shown that WDS can be used to determine the overall composition and therefore the Y2BaCuO5 content in these samples. It is also a powerful method to control chemical homogeneity and to investigate chemical modifications occurring during processing, especially those resulting from interaction between melt and substrate. The exact nature of YBa2Cu3O7−x nucleation and crystallization still presents many unsolved questions. Nanoanalysis allowed us to study Y2BaCuO5 dissolution in the peritectic liquid, and we have confirmed that it takes place exclusively by removing yttrium from Y2BaCuO5 particles. We have also shown the existence of an yttrium-rich liquid phase, i.e., with a higher yttrium concentration that can be deduced from the equilibrium phase diagram. A liquid phase having a composition close to that of YBa2Cu3O7−x can be inferred from this work. This suggests that YBa2Cu3O7−x nucleation and crystallization take place homogeneously from this liquid.