Chemical analysis in YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} melt-textured samples

A melt-textured process which involves the peritectic reaction Y{sub 2}BaCuO{sub 5}+liquid{r_arrow}YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} is the best method to develop bulk YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} superconductors with improved transport and magnetic properties. Up to this point, information regarding cationic stoichiometry in textured samples are 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 YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} textured samples. The melt-textured process generally modifies the sample stoichiometry. Thus, 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 Y{sub 2}BaCuO{sub 5} 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 of interaction between melt and substrate. The exact nature of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} nucleation and crystallization still present many unsolved questions. Nanoanalysis allowed us to study Y{sub 2}BaCuO{sub 5} dissolution in the peritectic liquid, and we have confirmed that it takes place exclusively by yttrium removingmore » from Y{sub 2}BaCuO{sub 5} particles. We have also shown the existence of yttrium-rich liquid phase, i.e., with a higher yttrium concentration that can be deduced from the equilibrium phase diagram. A liquid phase having composition close to that of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} can be inferred from this work. This suggests that YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} nucleation and crystallization take place homogeneously from this liquid. {copyright} {ital 1997 Materials Research Society.}« less

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