First-order transition in LK-99 containing Cu2S

LK-99 (Pb10-xCux(PO4)(6)O [0.9 < x < 1.1]) as a potential room temperature superconductor at ambient pressure has garnered significant attention. However, subsequent experiments conducted by various research groups worldwide have failed to observe the distinct resistivity drop of a superconducting-like transition in LK-99. A surge in misleading information about LK-99 calls for urgent clarification of its superconductivity. In this study, we have successfully reproduced the sharp resistivity drop in LK-99. We claim that the reduction in resistivity is a consequence of the first-order structural phase transition of Cu2S, occurring at approximately 400 K from the hexagonal phase at high temperature to the monoclinic phase at lower temperature. Furthermore, we confirm that LK-99, in its relatively pure form, behaves as a semiconductor rather than a superconductor.