Looking at something like $\ce{YBa2Cu3O7}$ which was one of the first cuprate superconductors to be discovered, I'm always curious how the selection of these substances as likely superconductors comes about?

Does it have to do with optimal crystalline structure, unpaired electrons, or is it similar to the way semiconductors are designed with doping to create "holes"? Or are these superconductors simply determined experimentally based on small changes of what has worked in the past?

As a side question: I've always been curious as to how they stumbled upon Yttrium for this particular case. It's not something I think of as being carried in ready supply. Would this have been after YAG lasers were already around?


2 Answers 2


Suffice to say, nobody really knows, and a Nobel prize surely awaits the first people who can explain the relationship between chemical composition and high-temperature superconductivity.

  • $\begingroup$ That's what my feeling was, but surely there must be some rule of thumb, right? Otherwise what would dictate experimental protocols and the like? $\endgroup$
    – jonsca
    May 12, 2012 at 8:27
  • 1
    $\begingroup$ Someone more qualified than I am will probably have more intelligent things to say here, but there is a lot that can be done with sheer brute force trial and error, looking at empirical trends and trying to extrapolate them (which is really another kind of educated trial and error). That's how a lot of science is done in the absence of guiding theoretical principles. $\endgroup$ May 12, 2012 at 8:34

Yttrium compounds were known before. Yttrium's similarities and differences to lanthanum are known and explained by trends in the periodic table. The discovery of the first ceramic oxide superconductors, which happened to contain $\ce{La}$, obviously led people to try substituting every possibly similar element in it experimentally.

One totally different thing from the design of semiconductors is: in superconductors, holes must be delocalized even without any thermal energy present whereas, in semiconductors, holes often become free to move away from dopant atoms because of thermal energy.

Crystalline structure (electronic structure aside) is important, but IMHO, that is even more challenging to predict theoretically from a given stoichiometric composition, precursors, and reaction conditions, than superconductivity from a given crystal structure. Sure, there are shared features in layered cuprates, but I doubt anybody chose them without having experimental experience before.

Theoretically, correlations between the superconducting transition temperature and features, such as phonon frequencies or, in case of cuprates, nickelates, and palladates, charge transfer gap energy, have led to some understanding of the upper limit of the former in certain families of materials. It also led some people to wrongly conclude the impossibility of higher transition temperatures overall.


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