Stabilization of superconducting LnPt 2B 2C by partial substitution of gold for platinum

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The quaternary intermetallic compounds LnPt 2B 2C (Ln=La, Pr and Y) were recently shown to be superconducting at temperatures up to 10.5 K. Annealing conditions were not found, however, which yielded single-phase material. Here it is reported that the partial substitution of Au for Pt in LnPt 2B 2C yields essentially single-phase polycrystalline material under annealing conditions readily accessible by conventional techniques. This is accomplished through arcmelting LnPt 1.5Au 0.6B 2C, a composition slightly superstoichiometric in transition metal, and annealing at 1100°C in Ta foil: a small amount of melt phase formed in the anneal is wicked away from the sample leaving good-quality material behind.