Single crystal synthesis, structure, and magnetism of Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$OThe recent claim of superconductivity above room temperature inPb$_{10-x}$Cu$_x$(PO$_4$)$_6$O with 0.9 < $x$ < 1 (referred to as LK-99) hassparked considerable interest. To minimize the influence of structural defectsand impurity phases on the physical properties, we have synthesized phase-puresingle crystals with $x \sim 1$. We find that the crystals are highlyinsulating and optically transparent. X-ray analysis reveals an unevendistribution of the substituted Cu throughout the sample. Temperature ($T$)dependent magnetization measurements for $ 2 \leq T \leq 800$ K reveal thediamagnetic response characteristic of a non-magnetic insulator, as well as asmall ferromagnetic component, possibly originating from frustrated exchangeinteractions in Cu-rich clusters in the Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$Ostructure. No anomalies indicative of phase transitions are observed. Wetherefore rule out the presence of superconductivity in Pb$_{9}$Cu(PO$_4$)$_6$Ocrystals, and provide some considerations on the origin of anomalies previouslyreported in experiments on polycrystalline specimen.arxiv.org

On the synthesis methodologies to prepare Pb$_9$Cu(PO$_4$)$_6$O -- phase, composition, magnetic analysis and absence of superconductivityWe present the results of our various attempts to prepare the presumablyroom-temperature and ambient-pressure superconducting compoundPb$_9$Cu(PO$_4$)$_6$O (LK-99). We experimented with various starting materials,and used several synthesis techniques like, sealed quartz tubes andair-sintering pathways to prepare the reported phase. Repetition of the exactsynthesis process followed by Lee et al failed to reproduce the superconductingphase yielding only a multiphase sample. None of our prepared samples exhibitsMeissner effect or Levitation. Very importantly, no copper (or only a traceamount) could be detected in any of the designated LK-99 phase with PXRDpattern identical to the reported one. Additionally, some dark greyish flakesin some samples responded towards the magnet in a way imitatinghalf-levitation. The magnetic measurement on those sample suggest it isdiamagnetic in the measured temperature range of 2-325 K but show a weak softferromagnetic behavior at 2 K, the origin of which is still unknown to us.arxiv.org

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