DIRECT GROWTH OF REBa_2Cu_3O_(7-#delta#) (RE =Yb, Er, Y, Dy, Eu, Sm, Nd AND Pr) FROM UNDERCOOLED MELT USING AERO-ACOUSTIC LEVITATOR

摘要

The authors have previously reported that the NdBa_2Cu_3C_(7-#delta#) (Nd123) phase solidifies directly from undercooled melt using an aero-acoustic levitator combined with a CO_2 laser in dry air flow. The reason why the YBa_2Cu_3C_(7-#delta#) (Y123) phase never undergoes primary solidification, however, remains unknown. There are systematic differences in the phase diagrams between stoichiometric Y123 and nonstoichiometric Nd123 with respect to the gradient of the liquidus line and the metastable high-temperature phase. In the present study, the containerless solidification of RE123 (RE=Yb, Er, Y, Dy, Eu, Sm, Nd and Pr) was carried out to compare systematically the direct growth of stoichiometric RE123 (sRE123) with that of nonstoichiometric RE123 (nRE123). In sRE123 specimens, the metastable high-temperature phase, the RE_4Ba_3O_9 (RE430) phase, solidified primarily from undercooled melt, while the nRE123 phase solidified primarily in nRE123 specimens. Moreover, in the Cu-enriched RE_3Ba_6Cu_(11)O_x Composition, the sRE123 phase solidified directly from the undercooled melt by suppressing the primary solidification of the RE430 phase. The direct growth of RE123, especially Y123, is discussed using the metastable phase diagram proposed on the basis of the experimental results.