INFLUENCE OF EXCESS YTTRIUM AND PLATINUM ON THE GROWTH-BEHAVIOR OF YBA2CU3O7-DELTA AND Y2BACUO5

The high temperature (1100 degrees C) coarsening of Y2BaCuO5 (211) and subsequent YBa2Cu3O7-delta (123) growth kinetics using melt quenched and 123 precursor powders were examined via quenching. Fine scale exce ss yttrium addition by sol gel coating was employed up to 20 mol perce nt. X-ray diffraction identified 211 fraction between 123 (similar to 30 wt.%) and melt quenched (similar to 10 wt.%) in the precursor powde rs. The addition of yttrium was seen to shift the 211 weight fraction to higher levels for the MQ powders. Refinement of the 211 particle si ze was seen in the presence of Pt but not with yttrium addition. The c oarsening behavior of 211 in either powder did not appear to significa ntly change with excess yttrium addition at 1100 degrees C. Differenti al thermal analysis showed that the 123 phase solidification temperatu re increased in the presence of Pt and reduced with yttrium addition u p to 10 mol %. Dilatometric measurements showed the influence of yttri um addition on the densification behavior of 123 due to the presence o f low temperature liquid phase formation. Directly inserting samples a t soak temperatures were seen to significantly alter the 211 weight fr action for 123 powder in contrast to slower thermal heating to tempera ture. However, this effect was not seen in the case of the melt quench ed precursor powder.