Superconducting YNi2B2C- and YPd2B2C-phase formation from undercooled melts

The effects of melt undercooling and composition on the phase selection in Y-Ni-B-C and Y-Pd-B-C melts has been studied by electromagnetic levitation experiments with particular respect to the superconducting phase formation. The suppression of the properitectic YB2C2 phase and direct growth of the superconducting YNi2B2C phase was achieved by quenching undercooled melt dr ops onto chill substrates. This results in homogeneous samples with narrow superconducting transition widths. Specimens with high volume fractions of the metastable superconducting YPd2B2C phase with T-c=21 K were obtained by the quenching of near-stoichiometric melts. The superconducting phase frac tions up to 40% far exceed those known from are-melted off-stoichiometric s pecimens. The operating window for metastable phase formation is discussed in the light of experimental results. (C) 2001 Elsevier Science B.V. All ri ghts reserved.