I think this theoretical result by Griffin at the Livermore Lab explains why labs are having difficulty replicating the LK-99 sample: https://arxiv.org/pdf/2307

I think this theoretical result by Griffin at the Livermore Lab explains why labs are having difficulty replicating the LK-99 sample: https://arxiv.org/pdf/2307.16892.pdf https://arxiv.org/pdf/2307.16892.pdf There are basically two repeating crystal cells. Her theoretical calculation shows superconducting properties when you substitute one cell for copper, but not the other. The "bad" substitution is a lower energy substitution that occurs more easily. "Finally, the calculations presented here suggest that Cu substitution on the appropriate (Pb(1)) site displays many key characteristics for high-TC superconductivity, namely a particularly flat isolated d-manifold, and the potential presence of fluctuating magnetism, charge and phonons. However, substitution on the other Pb(2) does not appear to have such sought-after properties, despite being the lower-energy substitution site. This result hints to the synthesis challenge in obtaining Cu substituted on the appropriate site for obtaining a bulk superconducting sample."