The influence of silver and Ag(In) alloy on Y-Ba-Cu-O equilibria around the YBa₂Cu₃O_7-δ superconducting phase

We investigated the effect of silver, Ag(In) alloy and Y₂BaCuO₅ (the so-called Y-211 green phase) on melt-textured samples of YBa₂Cu₃O_7-δ (Y-123) phase in order to check whether better grain growth and alignment were possible. We demonstrate that the addition of silver to Y-123 always led to an enhanced texture. The typical microstructure of the composite Y-123 plus Y-211 (that is believed essential for high critical currents in these high T_c superconductors) was not disturbed by addition of silver up to 7.5 wt% while higher concentrations of metal led to a degradation of the texture. Differential thermal analysis and thermogravimetric analysis were used to investigate the influence of silver and Ag(In) alloy on the Y-Ba-Cu-O equilibria around the Y-123 phase. We found a very unexpected thermal behaviour, similar to eutectic equilibrium, when the silver concentration was increased to 35 wt%. We believe that this effect was essentially due to the increasingly higher concentration of silver that could react with the impurities present in the melt.