THE INFLUENCE OF PROCESS PARAMETERS ON THE GROWTH-MORPHOLOGY OF LARGE-GRAIN PT-DOPED YBCO FABRICATED BY SEEDED PERITECTIC SOLIDIFICATION

We report an investigation of the processing of targe-grain Y-Ba-Cu-O (YBCO) containing 0.1, 0.2 and 0.5 wt% platinum (Pt) doping using seed ed peritectic solidification in a vertical tube furnace. In this study differential thermal analysis of the Pt-doped YBCO powders and carefu l temperature calibration of the furnace were performed in order to de termine optimum values of the thermal process parameters for each comp osition. The seeded melt process was observed to be extremely sensitiv e to the melting temperature, peritectic solidification temperature an d cooling rate during grain growth, and failure to optimize these para meters can result in various undesirable effects such as incomplete me lting, the nucleation of multiple grains and the formation of local re gions of impurity concentration within the sample. Scanning electron m icroscopy and vibrating sample magnetometry were employed to investiga te the microstructure and current-carrying capabilities of the samples . From these, 0.1 wt% Pt doping was determined to be sufficient for th e fabrication of melt-processed samples containing fine, sub-micron-si zed Y-211 particles which exhibited high critical current densities. N o improvement in sample properties was observed for higher levels of P t doping.