https://arxiv.org/abs/2308.13938

Ab initio Investigations on the Electronic Properties and Stability of Cu-Substituted Lead Apatite (LK-99) family with different doping concentrations (x=0, 1, 2)The pursuit of room-temperature ambient-pressure superconductivity in novel materials has sparked interest, with recent reports suggesting such properties in Cu-substituted lead apatite, known as LK-99. However, these claims lack comprehensive experimental and theoretical support. In this study, we address this gap by conducting ab initio calculations to explore the impact of varying doping concentrations (x = 0, 1, 2) on the stability and electronic properties of five compounds in the LK-99 family. Our investigations confirm the isolated flat bands that intersect the Fermi level in LK-99 (Pb9Cu(PO4)6O:Cu). In contrast, the other four parent compounds exhibit insulating behavior with wide band gaps. X-ray diffraction spectra based on the DFT simulations at 0K confirm the presence of Cu substitution on Pb(1) sites in the originally synthesized LK-99 sample, while an extra peak suggests potential alternative like Pb8Cu2(PO4)6 phases due to compositional variations in the original LK-99 samples. Furthermore, the LK-99 structure undergoes substantial lattice constriction, resulting in a significant 5.5% reduction in volume and 6.8% in area of two mutually inverted triangles formed by Pb(2) atoms. Meanwhile, energy calculations reveal a marginal energy preference for substituting Cu on Pb(2) sites over Pb(1) sites, with a difference of approximately 0.010 eV per atom (roughly 0.9645 k/mol). Intriguingly, at pressures exceeding 73 GPa, stability shifts towards LK-99 containing Cu substitutions on Pb(1) sites. Despite exhibiting higher electronic conductivity than parent compounds, Pb9Cu(PO4)6O:Cu falls short of the conductivity levels observed in metals or advanced oxide conductors with the simulation based on the Boltzmann transport theory.(1)>(1)>arxiv.org


원문 결론 5. Conclusions In this comprehensive investigation, we systematically explored the stability and electronic properties of Pb10-xCux(PO4)6O (x=0,1) and Pb8Cu2(PO4)6 (x=2), employing the ab initio approach. The key findings can be summarized as follows: (1). The electronic property result shows a set of isolated flat bands crossing the Fermi level solely emerges in Pb9Cu(PO4)6O: Cu, where Pb(1) denotes the substitution site, which is corresponding to LK-99. Such flat bands behavior hints Pb9Cu(PO4)6O: Cu can be a superconductor candidate, even though it may not be a room temperature superconductor. Meanwhile, the remaining four parent compounds exhibit insulating behavior characterized by wide band gaps, which explains why very different properties were claimed from the experimental observation from different groups. In practice, a strict control of sample stoichiometry and crystal structure would be the key. (1)>(1)>

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