A new protocol for the preparation of superconducting KBi 2 .

A superconducting KBi 2 sample was successfully prepared using a liquid ammonia (NH 3 ) technique. The temperature dependence of the magnetic susceptibility ( M / H ) showed a superconducting transition temperature ( T c ) as high as 3.6 K. In addition, the shielding fraction at 2.0 K was evaluated to be 87%, i.e. , a bulk superconductor was realized using the above method. The T c value was the same as that reported for the KBi 2 sample prepared using a high-temperature annealing method. An X-ray diffraction pattern measured based on the synchrotron X-ray radiation was analyzed using the Rietveld method, with a lattice constant, a , of 9.5010(1) Å under the space group of Fd 3̄ m (face-centered cubic, no. 227). The lattice constant and space group found for the KBi 2 sample using a liquid NH 3 technique were the same as those reported for KBi 2 through a high-temperature annealing method. Thus, the superconducting behavior and crystal structure of the KBi 2 sample obtained in this study are almost the same as those for the KBi 2 sample reported previously. Strictly speaking, the magnetic behavior of the superconductivity was different from that of a KBi 2 sample reported previously, i.e. , the KBi 2 sample prepared using a liquid NH 3 technique was a type-II like superconductor, contrary to that prepared using a high-temperature annealing method, the reason for which is fully discussed. These results indicate that the liquid NH 3 technique is effective and simple for the preparation of a superconducting KBi 2 . In addition, the topological nature of the superconductivity for KBi 2 was not confirmed.