UC Irvine

The metallic carbides exhibit many novel prototypes of crystalline structure. Among these compounds Th 2NiC 2 was reported in 1991 as a new carbide which crystallizes in the U 2IrC 2 prototype structure. In this work we report a reinvestigation of the synthesis of this compound. We find that Th 2NiC 2 is a new superconductor. Our results suggest that this phase is stable only at high temperatures in the system ThNiC. The substitution of Th by Sc stabilizes the phase and improves the superconducting properties. The highest superconducting critical temperature occurs at 11.2K with nominal composition Th 1.8Sc 0.2NiC 2. The electronic coefficient determined by specific heat measurements is close to zero. This unusual result can be explained by covalent bonding in the compound. © 2012 IOP Publishing Ltd.