A new protocol for the preparation of superconducting KBi2

Abstract

A superconducting KBi₂ sample was successfully prepared using a liquid ammonia (NH₃) 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 KBi₂ 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 Fdm (face-centered cubic, no. 227). The lattice constant and space group found for the KBi₂ sample using a liquid NH₃ technique were the same as those reported for KBi₂ through a high-temperature annealing method. Thus, the superconducting behavior and crystal structure of the KBi₂ sample obtained in this study are almost the same as those for the KBi₂ sample reported previously. Strictly speaking, the magnetic behavior of the superconductivity was different from that of a KBi₂ sample reported previously, i.e., the KBi₂ sample prepared using a liquid NH₃ 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 NH₃ technique is effective and simple for the preparation of a superconducting KBi₂. In addition, the topological nature of the superconductivity for KBi₂ was not confirmed.