Effect of BaSnO₃ additions in MPMG-processed YBCO

Many tentatives have been made these last years to increase the pinning properties of melt-textured YBaCuO by secondary phases additions. The results are more or less positive depending on the processing conditions and the reactivity of the dopant, especially its action on the size and shape of 211 particles. In this paper, the effect of BaSnO₃ additions up to 30 mol% on the microstructure and the superconducting properties of MPMG-processed YBCO is investigated. At high temperatures, BaSnO₃ reacts rapidly with the liquid phases to form few microns size inclusions of a stable Y-Ba-Sn-Cu-Pt-O phase. This phase is found to consume platinum and to favor 211 coarsening at high temperature. For 30% doping, the entire microstructure is strongly affected and for low levels of doping (2% and 5%), we could not evidence any improvement in the superconducting properties, compared to undoped samples. But when the doping level is increased up to 10%, one can locally find a high density of submicron size 211 inclusions and T_c enhancement is observed. In this case, we could obtain improved J_c(B) properties up to 110 000 A/cm², at 77 K in zero field.