The effect of Ag and Y-24W1 addition on the microstructure and superconducting properties of single grain Y–Ba–Cu–O

We have reported recently the fabrication of high performance, nano-composite Y–Ba–Cu–O (YBCO) bulk superconductors containing nano-sized Y2Ba4CuMO (Y-2411, where M is typically a transition metal element) phase inclusions that contribute effectively to flux pinning. However, these studies have revealed that the field trapping capability of YBCO bulk superconductors containing the Y-2411 phase is limited due to the presence of micro- and macro-cracks in the bulk sample microstructure. Here, we report the fabrication of nano-composite YBCO bulk superconductors containing Ag and W-based Y-2411 (i.e. Y2Ba4CuWOy) secondary phase inclusions (SPI's) in an attempt to investigate the influence of Ag content on the formation and propagation of a/b and c- axis micro- and/or macro-cracks in the Y-123 matrix. The crack density for samples containing Ag is observed to be significantly lower than for samples fabricated without Ag. A detailed study of the microstructures and superconducting properties of Ag-doped, nano-composite bulk YBCO is presented.