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

TL;DR

This study re-evaluates LK-99's properties, revealing that its superconducting-like behavior is likely due to Cu$_2$S$ influence, and concludes LK-99 is a diamagnetic semiconductor rather than a superconductor.

Contribution

The paper demonstrates that Cu$_2$S$ removal from LK-99 eliminates superconducting-like behavior, challenging previous claims of room-temperature superconductivity.

Findings

Cu$_2$S$ phase identified in LK-99 samples

Ammonia treatment removes Cu$_2$S$ phase

LK-99 behaves as 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.