Superconductivity at 18 K in yttrium sesquicarbide system, Y ₂C₃

In this study, we investigated superconductivity at 18 K in an yttrium sesquicarbide system, Y₂C₃, by a magnetization measurement, although this material with a maximum T_c of 11.5 K has already been investigated by Krupka et al. in J. Less-Common Met. 17 (1969) 91. The crystal structure of Y₂C₃ is a body-centered cubic (Pu₂C₃-type) structure, and the lattice parameters are varied by heat treatment conditions. The magnetization (M-H) curves of this compound show a typical type-II superconducting behavior, and the lower critical field, H_c1(0), is 3.5 mT. The T_c value in this system is changed in the range from 15 K to 18 K, depending on sintering conditions. The sintering conditions in this work are different from those in a previous work by Krupka et al. We successfully synthesized a new high-T_c phase in Y₂C₃.