Superconductivity at 15 K in the metastable ScNi2B2C compound.

Abstract

A superconducting transition around 15--16 K is reported for metastable, as-melted ${\mathrm{ScNi}}_{2}$${\mathrm{B}}_{2}$C samples. Zero resistivity ${\mathit{T}}_{\mathit{c}}$(zero) was observed at 14.6 K with ${\mathit{T}}_{\mathit{c}}$(onset) around 16.5 K. A consistent diamagnetic ${\mathit{T}}_{\mathit{c}}$ signal was observed around 14.8--15.6 K. The new superconducting phase was identified as isostructural to the quaternary ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C-type phase with tetragonal lattice parameters a=3.34 \AA{} and c=10.2 \AA{}. This superconducting phase is unstable due to the extremely small ${\mathrm{Sc}}^{3+}$ ionic size, where the Sc atom is located in the cavity formed by the B-Ni-B-C network and no superconducting transition could be observed down to 5 K after 1050 \ifmmode^\circ\else\textdegree\fi{}C annealing.