Influence of CeO2, BaCeO3 or PtO2 additions on the microstructure and the critical current density of melt processed YBCO samples

The present work is devoted to investigating the effect of CeO2, PtO2 and BaCeO3 additives on the Y2BaCuO5 morphology and the melt processing of YBCO. The samples were synthesized by the melt texture growth (MTG) process in order to observe the Y2BaCuO5 morphology in the liquid phase at high temperature, in the YBa2Cu3O7-x matrix resulting from the peritectic reaction, and the resulting microstructure of YBa2Cu3O7-x. It is concluded that these investigated dopants exhibit similar effects concerning the limitation of Y2BaCuO5 coarsening in the melt. The evolution of the aspect ratio (I/w) versus the additive content in the melt demonstrates the change of the morphology of the Y2BaCuO5 grains. The magnetization measurements were carried out on cleaved samples using a SQUID magnetometer at 77 K with H parallel to c axis. The best compromise between an homogeneous and submicrometre Y2BaCuO5 distribution through the textured area and a high critical current density corresponds to either 'YBa2Cu3O7-x + 20 mol% Y2BaCuO5 + 2 wt% CeO2' or 'YBa2Cu3O7-x + 20 mol% Y2BaCuO5 + 0.5 wt% PtO2'. The distinct effects of cerium and platinum dopings on the superconducting properties are revealed by the critical current density J(c) measurements. Indeed, the cerium doped sample exhibits a J(c) = 5.5 x 10(4) A cm(-2) in zero field with a relatively important field dependence behaviour: J(c)(1 T)/J(c)(0) = 40%. In contrast the platinum doped sample strongly reduces this field degradation of J(c) with J(c)(1 T)/J(c)(0) = 80%.