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Published online by Cambridge University Press: 31 January 2011
Rapidly quenched melt-spun ribbons of palladium-based borocarbides with large fractions of the superconducting phase (Tc > 20 K) have been obtained. Superconductivity in the Pd-based alloys seems to be metastable and exists only in the rapidly quenched state. Thus, while in the as-cast state the YPd2B2C ingot is found to be paramagnetic, the rapidly quenched ribbon superconducts and has a simple XRD pattern characteristic for a fcc lattice with a lattice parameter of 4.15 Å. A systematic study in an annealing sequence shows decay of the superconducting phase above 750 °C. The reduction in the integral intensities of XRD fcc peaks correlates well with the loss of the superconducting fraction on successive annealing. The recently reported tetragonal phase, attributed to the superconducting state in this system, is not found in any of our rapidly quenched samples. We present the phase diagrams indicating the optimum composition regimes for superconductivity in the Y–Ni–B–C and Y–Pd–B–C systems. From our magnetic data the values for the upper critical field Hc2(0), and the coherence length ξ(0) are estimated to be 10 Tesla and 57 Å, respectively, for the rapidly quenched YPd2B2C superconducting ribbons.