REACTIVITY AND PHASE EQUILIBRIA OF Y-Ba-Cu-O PARTLY MELTED UNDER ARGON IN NICKEL

Considerable improvement in the processing techniques of superconductors is necessary to control the reactivity of cuprates towards potential substrate materials. In this study, the reactivity of YBa₂Cu₂O_x, melt with nickel was assessed. YBa₂Cu₃O_x was partly melted in nickel at 1080°C under argon. Crystallized compounds indicated that a significant reduction of cuprates occurred due to a low oxygen potential which changes the formal copper valency (Cu₂₊→Cu₊). A substantial nickel contamination of the melt by the attack of the nickel took place with the formation of a nickel oxide skeleton which was selectively infiltrated by a Ba-Cu-O rich liquid. Such a selective mass transport produced a significant chemical demixing and an important modification in the stoichoimetry of the melt. This preferential mass transport, fractional crystallization as well as nickel contamination caused the formation of phases which resulted from an extensive evolution of the compositional path as well as the formation of Ni-doped cuprates.