The stability of YBa₂Cu₃O_7−x in contact with silver

Abstract

The stability of YBa₂Cu₃O_7−x (the 123 compound) in contact with silver (Ag) at temperatures below 900 °C was investigated by conducting SEM and EDX analyses on 123 agglomerates that were enclosed in a dense Ag matrix and subjected to various thermal treatments. The stability of the 123 agglomerates was found to depend heavily on the oxygen content in the Ag matrix. In the case of insufficient oxygen content in Ag, the 123 agglomerates, which were as large as 150 μm thick, decomposed readily at temperatures above 500 °C. The complete decomposition process can be summarized as continuous extraction of Ba from the 123 oxide into the surrounding Ag matrix and is proposed to be driven by high mutual solubilities between Ag and Ba under the oxygen-lean condition. Prolonged preoxygenation of the (123 + Ag) mixture powders at temperatures above 400 °C prevents the occurrence of 123 decomposition in compacted samples during subsequent heat treatment, suggesting that the critical oxygen content in Ag for stabilizing the 123 compound to be no higher than 10⁻³ at. % (the oxygen saturation solubility at 400 °C). The findings may have implications for the processing of other Ba-containing high-T_c superconducting oxides as well.