Microstructural control of NdBa2Cu3O7-δ superconducting oxide from highly undercooled melt by containerless processing

Containerless processing of NdBa2Cu3O7-delta (Nd123) superconducting oxide was achieved by combining aero-acoustic levitation with CO2 laser heating. Nd123 melt was undercooled to 1207 K below the peritectic temperature and congruently solidified. X-ray diffraction peaks of the processed specimen corresponded well with the standard ones of the tetragonal Nd123. The specimen annealed at 573 K in pure oxygen gas showed a high superconductive transition temperature (T-c) of 95.1 K. Moreover, the solidification process with different initial compositions was investigated and discussed; from the undercooled melt with a Cu-poor composition, a small amount of the Nd4Ba2Cu2O10 phase and the Nd123 phase were directly solidified. T-c values of about 94 K were obtained in Cu-poor specimens. On the other hand, the nonstoichiometric phase, Nd1-xBa2-xCu3O7-delta, was directly solidified from the undercooled melt with a Cu-rich composition. The T-c values decreased from 94.6 to 88.2 K with increasing the Cu concentration from that of stoichiometric Nd123. (C) 1999 Elsevier Science B.V. All rights reserved.