[Paper Review] Synthesis of possible room temperature superconductor LK-99:Pb$_9$Cu(PO$_4$)$_6$O

Kapil Kumar, N. K. Karn+1 more|arXiv (Cornell University)|Jul 31, 2023

X-ray Diffraction in Crystallography14 citations

TL;DR

The authors synthesize LK-99–like Pb9Cu(PO4)6O polycrystals using a two-step precursor method and 925°C heat treatment, but find no evidence of bulk room-temperature superconductivity or diamagnetism. Further heat-treatment studies are ongoing.

ABSTRACT

The quest for room-temperature superconductors has been teasing scientists and physicists, since its inception in 1911 itself. Several assertions have already been made about room temperature superconductivity but were never verified or reproduced across the labs. The cuprates were the earliest high transition temperature superconductors, and it seems that copper has done the magic once again. Last week, a Korean group synthesized a Lead Apatite-based compound LK-99, showing a T$_c$ of above 400$^\circ$K. The signatures of superconductivity in the compound are very promising, in terms of resistivity (R = 0) and diamagnetism at T$_c$. Although, the heat capacity (C$_p$) did not show the obvious transition at T$_c$. Inspired by the interesting claims of above room temperature superconductivity in LK-99, in this article, we report the synthesis of polycrystalline samples of LK-99, by following the same heat treatment as reported in [1,2] by the two-step precursor method. The phase is confirmed through X-ray diffraction (XRD) measurements, performed after each heat treatment. The room temperature diamagnetism is not evidenced by the levitation of a permanent magnet over the sample or vice versa. Further measurements for the confirmation of bulk superconductivity on variously synthesized samples are underway. Our results on the present LK-99 sample, being synthesized at 925$^\circ$C, as of now do not approve the appearance of bulk superconductivity at room temperature. Further studies with different heat treatments are though, yet underway.

Motivation & Objective

• Motivate the search for room-temperature superconductivity and reassess the LK-99 claim in Pb9Cu(PO4)6O.
• Reproduce the synthesis using the reported two-step precursor method.
• Verify phase formation with X-ray diffraction after each heat treatment.
• Test for room-temperature diamagnetism and bulk superconductivity indicators.
• Conclude whether bulk superconductivity is observed under the conditions tested.

Proposed method

• Synthesize polycrystalline LK-99–type Pb9Cu(PO4)6O via a two-step precursor method.
• Apply heat treatments following the same protocol as referenced in prior reports.
• Confirm phase formation after each heat treatment using X-ray diffraction (XRD).
• Measure room-temperature magnetic responses to assess diamagnetism (e.g., levitation tests).
• Evaluate signs of bulk superconductivity; report findings and limitations.
• Indicate that further heat-treatment variations are being explored.

Experimental results

Research questions

• RQ1 Does Pb9Cu(PO4)6O exhibit bulk superconductivity at room temperature under the tested synthesis conditions?
• RQ2 Is room-temperature diamagnetism detectable in the synthesized samples?
• RQ3 How does the phase purity, as verified by XRD after heat treatments, correlate with any superconducting or magnetic signals?
• RQ4 Can alternative heat-treatment pathways yield evidence of superconductivity?

Key findings

• Diamagnetism at room temperature is not evidenced by magnet levitation tests.
• The synthesized LK-99–type phase at 925°C does not show bulk superconductivity.
• XRD confirms the phase after each heat treatment, but no superconducting transition is observed.
• The authors state that the results do not approve the appearance of bulk superconductivity under the tested conditions.
• Further studies with different heat treatments are underway.