Microstructural control of NdBa 2Cu 3O 7−δ superconducting oxide from highly undercooled melt by containerless processing

Abstract

Containerless processing of NdBa 2Cu 3O 7− δ (Nd123) superconducting oxide was achieved by combining aero-acoustic levitation with CO 2 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 Nd 4Ba 2Cu 2O 10 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, Nd 1+ x Ba 2− x Cu 3O 7− δ , 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.