The Korean team appears to have been stuck for several years by the lack of reproducibility of this synthesis method. While it was a great discovery that has shown that this material must have some very interesting properties, perhaps even superconductivity at ambient temperature and pressure, in order to be able to measure its properties and be able to evaluate the possible practical applications, a much more precise method for enforcing the desired crystal structure is required, than mixing powders and baking them into a ceramic.
Perhaps such a method for producing samples with deterministic properties would be to develop first a method to grow monocrystals of the special kind of lead phosphate that forms the base crystal structure, maybe by drawing the crystals from melt.
Once monocrystals of this kind of lead phosphate are available, they could be doped with copper, e.g. by ion implantation. By controlling and varying the parameters of the process, e.g. the angle of incidence and the velocity of the ions and the thermal profile used for annealing, it is likely that reproducible samples can be produced, where the copper ions substitute lead in the useful places and not in the others.
By this method it would be possible to produce only thin layers of LK-99, but that should be enough to enable the characterization of the material.
Moreover, because LK-99 is very fragile, it is unlikely that it could be used to make cables or coils. Practical uses where LK-99 would be deposited as thin films are much more likely.
As an alternative to ion implantation, which might be able to produce thicker layers, perhaps once monocrystals of the base lead phosphate are available it may be possible to develop some method of chemical vapor deposition, to grow epitaxially a layer of LK-99 over the base crystal, but with such a method it is less obvious if there is any way to control which lead atoms are substituted, though this may depend on the orientation of the base crystal.
