CHEMICAL-ANALYSIS IN YBA2CU3O7-X MELT-TEXTURED SAMPLES

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 textur ed samples is rather lacking in the literature, In this work, waveleng th dispersive analysis (WDS) at a microscopic level and energy dispers ive x-ray analysis (EDX) at a nanoscopic level were used to characteri ze 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 a ccurate knowledge of the starting composition. We have shown that WDS can be used to determine the overall composition and therefore the Y2B aCuO5 content in these samples. It is also a powerful method to contro l chemical homogeneity and to investigate chemical modifications occur ring during processing, especially those resulting from interaction be tween melt and substrate. The exact nature of YBa2Cu3O7-x nucleation a nd crystallization still presents many unsolved questions. Nanoanalysi s allowed us to study Y2BaCuO5 dissolution in the peritectic liquid, a nd we have confirmed that it takes place exclusively by removing yttri um from YzBaCuO5 particles. We have also shown the existence of an ytt rium-rich liquid phase, i.e., with a higher yttrium concentration that can be deduced from the equilibrium phase diagram. A liquid phase hav ing a composition close to that of YBa2Cu3O7-x can be inferred from th is work. This suggests that YBa2Cu3O7-x nucleation and crystallization take place homogeneously from this liquid.