Synthesis and superconductivity of intermetallic compounds Y2NixB8−xC2, YNixCu2−xB2C, and YNixCu2−xSi2C

Borocarbide and silicocarbide intermetallic Y2NixB82xC2 (x = 1, 2, 3, 5), YNiCuB2C, and YNixCu22xSi2C (x = 0, 2) were prepared and their superconductivity was studied. The results indicated that with the change of the ratio of Ni to B in Y2NixB82xC2, secondary phases were introduced into YNi2B2C phase. A Tc of 15.0 K was observed for the compounds x = 2, 3, and 5, which originated from the major phase YNi2B2C in these samples. Partial substitution of Ni by Cu reduced the Tc to 11.0 K for YNiCuB2C. For Si substitution system, no bulk superconductivity was found in YNi2Si2C and YCu2Si2C. But a minor superconducting phase (Tc~4 K) with a volume fraction of the order of near 1% was observed in them. It was noticed that for the temperature dependent magnetization of superconducting compounds containing Ni, a significant difference between zero-field cooling and field cooling curves before Tc was always observed, which was tentatively attributed to Ni-containing impurity.