HIGH-PRESSURE-HIGH-TEMPERATURE EFFECT ON THE STRUCTURE OF YBACUO-BASED AND NDBACUO-BASED SUPERCONDUCTIVE CERAMICS

The structure of dense (99%) high-pressure (2-5 GPa)-high-temperature (700-1500 degrees C) treated single-phase and melt-textured YBaCuO and NdBaCuO ceramics has been investigated. High-pressure-high-temperatur e (HP-HT) treatment under 5 GPa in contact with annealed zirconia allo ws us to prevent oxygen losses from Nd123 and Y123 structures even whe n heated up to 1100 and 1400 degrees C, respectively, and thus, keep t he superconductive characteristics. For MT-YBaCuO ceramics, a more tha n twofold decrease in the anisotropy of critical current density occur s because of doubling critical current density in the direction of the c-axis of Y123 crystallites tin the perpendicular direction it remain s almost unchanged) may be explained by the increase in dislocation de nsity in the (001) plane (from 10(8) cm(-2) up to 10(12) cm(-2)) and b y narrowing of twin domains (from 150 down to 20 nm). For MT-NdBaCuO, narrowing of spacing between the twins has been observed in the polari zed optical microscope.