One odd thing that I've not seen any discussion on: the reported heat capacity of LK-99 decreases above 250K, which is pretty atypical. Has there been any commentary on that?
> Has there been any commentary on that? German, but nevertheless: http://blog.fefe.de/?ts=9a3f8740 "I work in the field [...] we don't believe a word of this. [...] The data set in Fig. 4(b) is also a treat. It is VERY unusual when the heat capacity decreases again at high temperatures. This can happen at low temperatures, but not at high temperatures. [...] My personal assumption is that the authors measured an ins…
"I work in the field and we discussed the preprint a bit in the research group this morning. In a nutshell, we don't believe a word of it:
Fig. 1(a) and (c) are implausible. Normally, this sort of thing looks like this. Note the gradual increase at low currents, this effect is especially expected for magnetic fields.
Also Fig. 1(d) cannot be correct. At Tc ~ 400K the Meissner effect would displace a much stronger field than 10 Oe = 1 mT. I.e. the distinction between FC (field cooled) and ZFC (zero-field cooled) should not be so pronounced. It should look more like this.
But in this case the temperature dependence does not agree at all with the critical currents of Fig. 1(a) and (c).
And also that ALL values in Fig. 1(d) are negative is extremely unusual, but this could perhaps be argued.
The data set in Fig. 4(b) is also a treat. It is VERY unusual to see the heat capacity decrease again at high temperatures. This can happen at low temperatures, but rather not at high temperatures.
I know the described experimental setup / cryostat very well. There is no reasonable reason why the authors did not measure at higher temperatures to show that the behavior above Tc ~ 400K is significantly different. E.g. a temperature dependence of the resistance would have been mandatory.
In general, the paper is very poorly written. The data are not adequately discussed, the explanations are poor, and the papers cited are rather, shall we say, meager. This does not inspire confidence in what the authors have measured and want to have seen there.
My personal guess is that the authors measured an insulator, accordingly no current flowed, and thus no voltage occurred (4-point measurement). Then it looks like a superconductor. But if you then turn up the current (i.e. the applied voltage), there may be breakdowns and a current starts to flow. This would explain the sudden increase."