Interfacial reactions between Y₁Ba₂Cu₃O_7−x and Ag–Pd alloys during high temperature heat treatments

Abstract

The interfacial reactions between the Y₁Ba₂Cu₃O_7−x (123) compound and a Ag₇₀Pd₃₀ alloy have been studied for several heat treatments below and above the melting point of the superconductor. Scanning and transmission electron microscopy, energy dispersive x-ray analysis, Auger spectroscopy, and x-ray diffraction have been used to characterize the reaction products. For the heat treatments below the melting point of the superconductor (950 °C), the Ba and Cu of the 123 compound migrate to the interface and react with the Pd to form a body-centered cubic phase Ba(Pd, Cu)O₂. This structure is formed by substitution of Cu by Pd on the Cu⁺² sites of the BaCuO₂ structure (Im3m space group). CuO is also found in some areas as a product of the reaction. For the thermal treatments above the melting point of the superconductor, the reaction products are the same but, in this case, a large number of Y₂BaCuO₅ precipitates are found in the bulk of the superconductor near the interface. Pure Ag particles have also been observed in the 123 compound at distances relatively far from the interface.