STUDIES OF THE PHASE EVOLUTION OF YBCO MATERIALS WITH DIFFERENT ADDITIVES

Y123 samples with varying amounts of added Y211, PtO2 and CeO2 have be en melt processed and quenched from temperatures between 960 degrees C and 1100 degrees C. The microstructures of the quenched samples have been characterized using a combination of x-ray diffractometry, optica l microscopy, scanning electron microscopy, microprobe analysis, energ y-dispersive x-ray spectroscopy and wavelength-dispersive x-ray spectr oscopy. The Ba-Cu-O-rich melt undergoes complex changes as a function of temperature and time. A region of stability of BaCuO2 (BC1) and BaC u2O2 (BC2) exists below 1040 degrees C in samples of Y123 + 20 mol% Y2 11. Ba2Cu3O5 is stabilized by rapid quenching but appears to separate into BC1 and BC2 at lower quenching rates. PtO2 and CeO2 additions aff ect the distribution and volume fractions of the two Ba-Cu-oxide phase s.