(Ba,K)BiO3 constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature Tc of 30 K arises in proximity to charge density wave order. However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO3 with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO3. The parent compound BaSbO3−δ shows a larger charge density wave gap compared to BaBiO3. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to Tc = 15 K. This value is lower than the maximum Tc of (Ba,K)BiO3, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO3 indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.
Predominant oxygen holes may be a sufficient condition for a higher Tc.
SOURCE – Nature
Written by Brian Wang, Nextbigfuture.com
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I agree the graph is a bit unclear, particularly if you remove it from the paper where the meaning of _x_ is defined, but the actual units of the x axis would be the particularly unhelpful $text{ionic cell}^{-1} [K]$, or something very similar to that.
so percent potassium….sorta
This graph would have lost you points in my engineering labs, for lack of units.
> (…) Polycrystalline samples of BKSO with potassium content x from 0 to 0.75 were synthesized (…)
According to this statement, it is the fraction of Potassium, so $Ba_{1-x}K_xSbO_3$ is the generic formula.
Perhaps my question was not clear. The horizontal axis of the phase diagram is labeled "x". What are the units of x?
Perhaps I am dense, but it is not obvious to me. Is it fraction by mass of Barium, of Potassium???
Even then, look at the temperature scale. These new superconductors operate under 20 degrees K.
I'd much more like to see progress made on increasing the operating temperature. Hopefully get it up around room temperature. This was the promise they made over 30 years ago.
Much like working fusion reactors however…
This was my thought. I understand the science juuuust enough to think this would have positive effects for fusion power start-ups.
What are the units of "x"?
What is the critical current and critical magnetic field? If this superconductor could reach higher levels in these two parameters than the "normal" high Tc superconductor, this would allow even higher magnetic fields at *low* temperatures.
I.e. all the fusion start-ups would get a significant boost…