Investigation of the melt-growth process of YbBa2Cu3O7−δ powder in Ag-sheathed tapes

We investigated the melt-growth behavior of YbBa2Cu3O7−δ (Yb123) powder under different atmospheres for potential application in Ag-sheathed Yb123 wires. We chose Yb123 because it has the lowest melting temperature of the RE123 (RE = rare earth) phases. Yb123 needs to be melted under low oxygen partial pressure (pO2) to depress its melt temperature below that of Ag. Here we report that adding Ag powder to Yb123 powder or encasing Yb123 powder in a Ag-sheath further decreases the melting temperature of Yb123. We designed a heat treatment process in which we varied the pO2 during the heat treatment to melt the Yb123 in a Ag-sheathed powder-in-tube (PIT) wire and then regrow Yb123 on cooling. Based on these studies, we have developed a model for Yb123 melting and growth.