THE 23-K SUPERCONDUCTING PHASE YPD2B2C

We have carried out a systematic structural, electric, and magnetic st udy on Y-Pd-B-C samples with different compositions with emphasis on t he as-cast and annealed YPd5B3C0.3 which was first reported to superco nduct at approximately 23 K by Cava et al. We found that the tetragona l body-centered YPd2B2C with lattice parameters a = 3.71 angstrom and c = 10.81 angstrom is the phase responsible for the 23 K superconducti vity and that YPd2B2C is metastable, which is consistent with the sugg estion made by Cava et al. [1]: it is not stable at high temperatures nor stabilizable by Ni doping, although its isostructural compound, YN i2B2C, exists. Two new phases with Y:Pd ratios of 1:7 and 2:3, respect ively, have also been detected.