Direct growth of REBa 2Cu 3O 7-δ (RE=Yb, Er, Y, Dy, Eu, Sm, Nd and Pr) from undercooled melt using aero-acoustic levitator

Abstract

The authors have previously reported that the NdBa 2Cu 3O 7-δ (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 3O 7-δ (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 11O 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.