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The copper substituted lead oxyapatite,Pb$_{10-x}$Cu$_{x}$(PO$_{3.92(4)}$)$_{6}$O$_{0.96(3)}$ (x=0.94(6)) was studiedusing neutron and x-ray diffraction and neutron spectroscopy techniques. Thecrystal structure of the main phase of our sample, which has come to becolloquially known as LK-99, is verified to possess a hexagonal structure withspace group $P 6_{3}/m$, alongside the presence of impurity phases Cu andCu$_2$S. We determine the primary substitution location of the Cu as the Pb1($6h$) site, with a small substitution at the Pb2 ($4f$) site. Consequently, noclear Cu-doping-induced structural distortion was observed in the investigatedtemperature region between 10~K and 300~K. Specially, we did not observe areduction of coordinate number at the Pb2 site or a clear tilting of PO$_4$tetrahedron. Magnetic characterization reveals a diamagnetic signal in thespecimen, accompanied by a very weak ferromagnetic component at 2 K. Nolong-range magnetic order down to 10 K was detected by the neutron diffraction.Inelastic neutron scattering measurements did not show magnetic excitations forenergies up to 350 meV. There is no sign of a superconducting resonance in theexcitation spectrum of this material. The measured phonon density of statescompares well with density functional theory calculations performed for themain LK-99 phase and its impurity phases. Our study may shed some insight intothe role of the favored substitution site of copper in the absence ofstructural distortion and superconductivity in LK-99.

Structure and lattice excitations of the copper substituted lead oxyapatite Pb$_{9.06(7)}$Cu$_{0.94(6)}$(PO$_{3.92(4)}$)$_{6}$O$_{0.96(3)}$