First order transition in Pb\(_{10-x}\)Cu\(_x\)(PO\(_4\))\(_6\)O (\(0.9<x<1.1\)) containing Cu\(_2\)S

Abstract

Lee et al. reported that the compound LK99, with a chemical formula of Pb\(_{10-x}\)Cu\(_x\)(PO\(_4\))\(_6\)O (\(0.9<x<1.1\)), exhibits room-temperature superconductivity under ambient pressure. In this study, we investigated the transport and magnetic properties of pure Cu\(_2\)S and LK-99 containing Cu\(_2\)S. We observed a sharp superconducting-like transition and a thermal hysteresis behavior in the resistivity and magnetic susceptibility. However, we did not observe zero-resistivity below the transition temperature. We argue that the so-called superconducting behavior in LK-99 is most likely due to a reduction in resistivity caused by the first order structural phase transition of Cu\(_2\)S at around 385 K, from the \(\beta\) phase at high temperature to the \(\gamma\) phase at low temperature.