Superconductivity in the copper-poor region of the Ca(Cu, Si)2−x system

We report the discovery of superconducting materials Ca(Cu, Si)2−x. The results of magnetic susceptibility and electrical resistivity measurements on two phase Ca-Cu-Si samples with nominal compositions CaCu0.25Si1.75, CaCu0.33Si1.67 and CaCu0.25Si1.7 provide evidence for bulk superconductivity in a hexagonal AlB2-type majority fraction of the sample volume. Powder X-ray diffraction patterns indicate that the minor impurity phase is the element Si which has no effect on the superconductivity. CaCuxSi2−x samples with excess Cu component (x ⩾ 0.4) showed no evidence of superconductivity for T ⩾ 1.8 K. Under the annealing conditions required for the fabrication of the AlB2-type superconductor, the best sample with the nominal composition CaCu0.25Si1.7 annealed for three days at 1000 °C exhibits the transition temperature Tc ∼ 3.2 K, as determined by magnetic susceptibility and electrical resistivity measurement techniques.