The characteristics of LK-99 by Cu${}_2$S removal using ammonia solution: A diamagnetic semiconductor

Abstract

In this study, we re-evaluated the superconducting properties of LK-99. The LK-99 samples were synthesized using the process proposed by the original Korean team. Additionally, we examined whether the results of the Korean team are related to Cu${}_2$S by using ammonia solution (NH${}_3$-H${}_2$O) to remove Cu${}_2$S . Through x-ray diffraction (XRD) analysis, a distinct Cu${}_2$S phase was identified in the LK-99 samples. A subsequent treatment using an ammonia solution effectively eliminated this phase. The appearance of blue Cu${}^{+2}$ ions in the solution and the elimination of the Cu${}_2$S peak in XRD support the conclusion. The magnetic and electrical properties of LK-99 with and without Cu${}_2$S postulate that the superconducting-like behavior in LK-99 predominantly arises from a transition in resistivity due to the influence of Cu${}_2$S . As such, LK-99 is better classified as a diamagnetic semiconductor than a room-temperature superconductor. The room-temperature superconductors still require further research.