The characteristics of Cu-doped lead apatite (LK-99) synthesized with the removal of Cu₂S using ammonia solution: A diamagnetic semiconductor

This study evaluated the superconducting properties of Cu-doped lead apatite "LK-99" and synthesized LK-99 samples using the process proposed by a team from Korea, who first described the process. Additionally, whether the results of this Korean team were related to Cu2S was also examined using an ammonia solution (NH3H2O) to remove Cu2S. Through x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX) analyses, a distinct Cu2S phase was identified in the LK-99 samples. This phase was effectively eliminated through a subsequent treatment using an ammonia solution. The appearance of blue Cu+2 ions in the solution and the elimination of the Cu2S peak in XRD supported the conclusion. The magnetic and electrical properties of LK-99 with and without Cu2S suggest that the superconductor-like behavior in LK-99 predominantly arises from a transition in resistivity due to the influence of Cu2S. As such, LK-99 is better classified as a diamagnetic semiconductor than a room-temperature superconductor. The room-temperature superconductors still require further research.