Behavior of silver substitution in single-grain TSMG YBCO bulk superconductor

Ag concentration in the single-grain TSMG Y1Ba2(Cu1−xAgx)3O7 bulk superconductor with nominal Ag concentration for x = 0.05 was measured by WDX microprobe. The partition coefficient of Ag between Y123 crystal and the melt, kAg, was estimated to be kAg = 0.1. It is also shown that the solubility of Ag in the Y2BaCuO5 phase is below the WDX detection limit. As the measured Ag concentration is about four times higher than the concentration of Ag for optimum chemical pinning, the clustering of Ag atoms is supposed and a mechanism of Ag clustering is proposed.