INFLUENCE OF CEO2, BACEO3 OR PTO2 ADDITIONS ON THE MICROSTRUCTURE ANDTHE 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 processin g of YBCO. The samples were synthesized by the melt texture growth (MT G) process in order to observe the Y2BaCuO5 morphology in the liquid p hase 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 effec ts concerning the limitation of Y2BaCuO5 coarsening in the melt. The e volution 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 us ing a SQUID magnetometer at 77 K with H parallel to c axis. The best c ompromise between an homogeneous and submicrometre Y2BaCuO5 distributi on through the textured area and a high critical current density corre sponds to either 'YBa2Cu3O7-x + 20 mol% Y2BaCuO5 + 2 wt% CeO2' or 'YBa 2Cu3O7-x + 20 mol% Y2BaCuO5 + 0.5 wt% PtO2'. The distinct effects of c erium and platinum dopings on the superconducting properties are revea led by the critical current density J(c) measurements. Indeed, the cer ium 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%.