Abstract
This paper shows the parameters to affect the critical characteristic of YBaCuO superconducting bulk fabricated by MPMG (Melt Powdered Melt Growth)process. In order to investigate proper processing variables, the effect of the holding time at the melting temperature and that of the slow cooling time in $O_2\; ambient\; on\; the\; J_c$ were experimented. And then with the above obtained heat treatment conditions, the effects of addition of $Y_2BaCuO_5\; and\; Ag\; on\; the\; J_c$ were also investigated. A proper slow cooling time yields phase transformation from Tetragonal $(YBa_2Cu_3O_6)$ to Orthorhombic $(YBa_2Cu_3O_7)$ during an annealing time in $O_2$. Ag addition plays a role in increasing the $T_c\; and\; the J_c$, but the magnetization decreases. The $J_c$ and the magnetization increase with addition of Y211. $J_c$ of the sample added Ag 10wt% is superiorover 3000 G. Proper holding time, slow cooling time and amount of impurity addition are important parameters in fabricating the YBaCuO bulk by MPMG process with high $J_c$.