We report apparent drops in electrical resistivity and diamagnetic susceptibility transitions at 315 K in solid-state-synthesized Pb9Cu(PO4)6O polycrystals containing trace Cu2S impurity phases. Four-probe transport measurements on pressed pellets suggest a sharp transition near 312 K.
Pressed polycrystalline pellets exhibit an abrupt drop in apparent voltage drop at 312 K under 1 mA excitation current.
Zero-field-cooled (ZFC) susceptibility shows a negative signal at 10 Oe, without flux-pinning or specific heat capacity confirmation.
Pending author upload of revised After Manuscript.
0000-0001-6642-3190 ·
[ORIGINAL REVIEWER · Round 1 on v1]
Public Evaluation: The sharp resistivity drop at 312 K coincides with the known first-order structural phase transition of Cu2S (chalcocite) from monoclinic to hexagonal at 310–315 K, not bulk superconductivity.
Technical Critique / Verification Checklist: Major revision required: either synthesize phase-pure single crystals free of Cu2S and demonstrate zero resistance below 1e-9 Ohm-cm, or revise the manuscript claims to characterize the Cu2S phase transition.
0000-0001-9921-4402 ·
[ORIGINAL REVIEWER · Round 1 on v1]
Public Evaluation: Powder XRD patterns in Figure 2 show 8 wt% Cu2S secondary phase peaks. Without Meissner flux expulsion and specific-heat anomaly data, the claim of superconductivity requires major experimental revision.
Technical Critique / Verification Checklist: Requires Rietveld refinement after chemical etching of Cu2S impurities and AC susceptibility harmonic measurements in the next version.
0000-0003-1182-7741 ·
[ORIGINAL REVIEWER · Round 1 on v1]
Public Evaluation: While the authors uploaded their raw lock-in amplifier traces to Zenodo, re-plotting the V-I curve on a log-log scale shows ohmic contact resistance rather than a superconducting critical current.
Technical Critique / Verification Checklist: Major revision requested: either reframe the manuscript as a quantitative study of Cu2S percolative metal-insulator transitions or provide genuine Meissner effect evidence.
0000-0002-5501-8832 ·
[ORIGINAL REVIEWER · Round 1 on v1]
Public Evaluation: Independent thermodynamic and transport analysis confirms that the 312 K transition is caused by the Cu2S impurity phase transition.
Technical Critique / Verification Checklist: Major revision required on v1. There is no time limit: once the authors overhaul sample purity and upload v2, our original 4-reviewer panel plus 1–2 newly invited fresh reviewers will verify the revision.