MICROSTRUCTURAL STUDIES OF QUENCHED PARTIALLY-MELTED Y-123 MATERIALS AND Y-123 WITH Y-211, PTO2 AND CEO2 ADDITIONS

The microstructure of YBa2Cu3O7-delta (Y-123) materials partially-melt ed in air and quenched from the temperature range 900-1100 degrees C, has been characterized using a combination of X-ray diffractometry, op tical microscopy, scanning electron microscopy, electron microprobe an alyses, transmission electron microscopy and energy and wave dispersiv e X-ray spectrometries. The microstructural studies reveal significant changes in the character of the quenched partial-melt as a function o f temperature and time before quenching. BaCu2O2 and BaCuO2 are found to co-exist in stoichiometric samples quenched from the temperature ra nge 920-960 degrees C. Under suitable cooling conditions, large pocket s of melt cristallize as BaCuO2 with an exsolution of BaCu2O2 in the f orm of thin plates (approximate to 50-100 nm thick) along facets. Y2Ba CuO5 (Y-211) additions are associated with the formation of BaCu2O2 at 1100 degrees C. Preliminary results on the effects of PtO2 and CeO2 a dditions to Y-123 (and Y-123 with Y-211 additions) show that these enh ace the formation of BaCu2O2 at the melting temperature of 1100 degree s C. (C) 1998 Elsevier Science S.A. All rights reserved.